BIO - TERMS - FREQUENCY > 4 Flashcards

Question

cation

Answer 1

Ion with a positive charge; e.g., Na+. // A positively charged ion.

Answer 2

The nonstaining constriction of a chromosome that is the point of attachment of the spindle fiber. // Constricted region of a mitotic chromosome that holds sister chromatids together. This is also the site on the DNA where the kinetochore forms so as to capture microtubules from the mitotic spindle. // The region of the chromosome that interacts with microtubules during mitosis. // A specialized site in a chromosome, serving as the attachment point for the mitotic or meiotic spindle. // Spindle-fiber attachment region of a chromosome.

Answer 3

A protein that helps nascent polypeptides fold into their proper three-dimensional structures. // Any of several classes of proteins or protein complexes that catalyze the accurate folding of proteins in all cells. // A protein that assists in the folding of other proteins. // A protein that facilitates the folding of other polypeptide chains, the assembly of multimeric proteins, or the formation of macromolecular assemblies (e.g., chromatin). Also called molecular chaperone. (Chapters 4, 12, and 13) // Protein that helps guide the proper folding of other proteins, or helps them avoid misfolding. Includes heat-shock proteins (hsp). // A protein that can fold or unfold other molecules. These proteins bind reactive trace elements and ferry them to different parts of the cell for delivery.

Answer 4

Movement of cell or organism in response to chemicals. // Attraction or repulsion of organisms by a diffusing substance. // Movement of a cell toward or away from some diffusible chemical. // A cell’s sensing of and movement toward or away from a specific chemical agent. // Cellular movement occurring in response to chemical signals in the environment. // Movement in response to the presence of a chemical.

Answer 5

Organelle in green algae and plants that contains chlorophyll and carries out photosynthesis. // The organelle that performs photosynthesis in photoautotrophic eukaryotes. // A green organelle in the cytoplasm of plants that contains chlorophyll and in which starch is synthesized. A mode of cytoplasmic inheritance, independent of nuclear genes, has been associated with these cytoplasmic organelles. // Chlorophyll-containing photosynthetic organelle in some eukaryotic cells. // Important compartment of plant cells; site of photosynthesis; chloroplasts have their own DNA replication, transcription, and ribosomes. Originated from cyanobacteria.

Answer 6

Genetic material of the nucleus in a nondividing cell. // A filamentous complex of DNA, histones, and other proteins, constituting the eukaryotic chromosome. // Complex of DNA, histones, and non-histone proteins found in the nucleus of a eukaryotic cell. The material of which chromosomes are made. // DNA complexed with histones. // The complex of DNA and proteins in eukaryotic chromosomes; originally named because of the readiness with which it stains with certain dyes. // The three-dimensional molecular structure of DNA and proteins in the nuclei of cells. // Threadlike, uncondensed DNA in an interphase eukaryotic cell.

Answer 7

The most compact form of genetic material; a single long molecule of DNA and associated proteins; becomes visible only when the cell is dividing. // Structure composed of a very long DNA molecule and associated proteins that carries part (or all) of the hereditary information of an organism. Especially evident in plant and animal cells undergoing mitosis or meiosis, during which each chromosome becomes condensed into a compact rodlike structure visible in the light microscope. // The DNA-containing structures that occur in the nuclei of living cells. // The structure that carries hereditary information, chromosomes contain genes. // A single large DNA molecule and its associated proteins, containing many genes; stores and transmits genetic information. // A structure in the cell nucleus containing a single linear thread of DNA. // Darkly staining nucleoprotein bodies that are observed in cells during division. Each chromosome carries a linear array of genes.

Answer 8

A cyclic pathway for the oxidation of acetyl residues to carbon dioxide, in which formation of citrate is the first step; also known as the Krebs cycle or tricarboxylic acid cycle. // A cyclic metabolic pathway that occurs in the matrix of mitochondria during which energy in the bonds of acetyl CoA is transferred to form ATP, NADH, and FADH2. // The metabolic pathway by which acetyl CoA is degraded to CO2. // Central metabolic pathway found in aerobic organisms. Oxidizes acetyl groups derived from food molecules, generating the activated carriers NADH and FADH2, some GTP, and waste CO2. In eukaryotic cells, it occurs in the mitochondria. // An alternative name for the citric acid cycle by which acetyl CoA is degraded to CO2. // A pathway that converts two-carbon compounds to CO2, transferring electrons to NAD+ and other carriers; also called tricarboxylic acid (TCA) cycle or critic acid cycle. // An alternative name for the citric acid cycle, by which acetyl CoA is degraded to CO2.

Answer 9

Ability of a B cell to produce a different class of antibody against one antigen. // A change in the class of the immunoglobulin expressed by a B lymphocyte. // Change from making one class of immunoglobulin (for example, IgM) to making another class (for example, IgG) that many B cells undergo during the course of an adaptive immune response. Involves DNA rearrangements called class-switch recombination. // A somatic gene recombination process in activated B cells that replaces one heavy-chain constant region with one of a different isotype, switching the isotype of antibodies from IgM to the production of IgG, IgA, or IgE. This affects the antibody effector functions but not their antigen specificity. Also known as isotype switching. Cf. somatic hypermutation. // An irreversible change at the DNA level when a B cell switches from making IgM and IgD to making one of the secondary classes of immunoglobulin.

Answer 10

A population of cells all derived from the same progenitor cell. // A population of genetically identical cells that are descended from the same ancestral cell. // A population of cells arising from a single parent cell. // All the individuals derived by vegetative propagation from a single original individual. In molecular biology, a population of identical DNA molecules all carrying a particular DNA sequence from an organism. // The descendants of a single cell.

Answer 11

A base triplet on messenger RNA that specifies an amino acid. // A sequence of three bases in a nucleic acid that codes for one amino acid. // Group of three nucleotide bases in a messenger RNA molecule. // A sequence of three adjacent nucleotides in a nucleic acid that codes for a specific amino acid. // A sequence of three nucleotides in mRNA that specifies the insertion of an amino acid into a polypeptide. // A set of three adjacent nucleotides in an mRNA molecule that specifies the incorporation of an amino acid into a polypeptide chain or that signals the end of polypeptide synthesis. Codons with the latter function are called termination codons. // A three-base sequence on a messenger RNA chain that encodes the genetic information necessary to cause a specific amino acid to be incorporated into a protein. Codons on mRNA are read by complementary anticodons on tRNA. // Sequence of three nucleotides in a DNA or mRNA molecule that represents the instruction for incorporation of a specific amino acid into a growing polypeptide chain. // Three contiguous bases in an mRNA template that specify the amino acids incorporated into protein. (Chapter 11)

Answer 12

Organic molecules assisting in enzyme function; e.g., NAD+. // A substance necessary for the activity of an enzyme. // Small molecule tightly associated with an enzyme that participates in the reaction that the enzyme catalyzes, often by forming a covalent bond to the substrate. Examples include biotin, NAD+, and coenzyme A. // A nonprotein substance that is associated with and that activates an enzyme. // A small organic molecule that acts as a cofactor in a biological reaction. // An organic cofactor required for the action of certain enzymes; often has a vitamin component.

Answer 13

Outer region of an organ; e.g., cerebral cortex, adrenal cortex. // The cytoskeletal network in the cortical region of the cytosol just beneath the plasma membrane. // The protective fungal covering of a lichen. // Any collection of neurons that forms a thin sheet, usually at the brain’s surface. // The outer part of a tissue or organ; in lymph nodes it refers to the follicles, which are mainly populated by B cells.

Answer 14

A bond in which an electron pair is equally shared by protons in two adjacent atoms. // A chemical bond that involves sharing of electron pairs. // A bond formed by sharing electrons between atoms. // A chemical bond in which the electrons of one atom are shared with another atom. // A chemical bond in which two atoms share electrons that interact with the nuclei of both atoms, lowering the potential energy of each through electrostatic interactions. // Stable chemical link between two atoms produced by sharing one or more pairs of electrons. // Strong chemical bond formed by a binding electron pair. // Chemical bond formed when atoms share electrons.

Answer 15

A second messenger formed from adenosine triphosphate by the action of the enzyme adenylyl cyclase. // A second messenger of many hormones. // A second messenger used when some hormones or neurotransmitters act on a target cell. Formed when adenylate cyclase reacts with ATP. // Adenosine-3′, 5′-monophosphate, a small molecule that must be bound by the catabolite activator protein (CAP) in order for the complex (CAP/cAMP) to bind to the promoters of operons and stimulate transcription. // A second messenger; its formation in a cell by adenylyl cyclase is stimulated by certain hormones or other molecular signals. // A molecule derived from ATP, in which the phosphate group has a cyclic structure; acts as a cellular messenger. // Nucleotide that is generated from ATP by adenylyl cyclase in response to various extracellular signals. It acts as a small intracellular signaling molecule, mainly by activating cAMP-dependent protein kinase (PKA). It is hydrolyzed to AMP by a phosphodiesterase. (Figure 15–25)

Answer 16

Protein that regulates and facilitates immune system activity. // Extracellular signal protein or peptide that acts as a local mediator in cell–cell communication. // One of a family of small secreted proteins (such as interleukins or interferons) that activate cell division or differentiation by binding to plasma membrane receptors in target cells. // A small protein released from human cells that regulates the immune response; directly or indirectly may induce fever, pain, or T cell proliferation. // Biologically active proteins released by activated lymphocytes and monocytes/macrophages. // Proteins made by a cell that affect the behavior of other cells, particularly immune cells. Cytokines made by lymphocytes are often called interleukins (abbreviated IL). Cytokines and their receptors are listed in Appendix III. Cf. chemokines. // Soluble proteins produced by cells in response to various stimuli, including virus infection; they aff ect the behavior of other cells both locally and at a distance, by binding to specifi c cytokine receptors. (Chapters 3 and 4)

Answer 17

The portion of a cell’s contents outside the nucleus but within the plasma membrane; includes organelles such as mitochondria. // All cellular contents contained between the plasma membrane and the nucleus; includes cytosol, organelles, and inclusions. // Basic compartment of the cell (surrounded by the plasma membrane) in which nucleus, endoplasmic reticulum, mitochondria and other organelles are embedded. // Cellular material contained by the cell membrane, including the organelles but excluding the nucleus. // Contents of a cell that are contained within its plasma membrane but, in the case of eukaryotic cells, outside the nucleus. // In a prokaryotic cell, everything inside the plasma membrane; in a eukaryotic cell, everything inside the plasma membrane and external to the nucleus. // The protoplasm of a cell outside the nucleus in which cell organelles (mitochondria, plastids, and the like) reside; all living parts of the cell except the nucleus.

Answer 18

The filamentous network that provides structure and organization to the cytoplasm; includes actin fi laments, microtubules, and intermediate filaments. // Organized network of protein filaments and hollow tubules that provide organization, support, and movement of the cell. // A complex system of fibers and filaments that provides support for cells and that is involved in moving the components of cells throughout the cytoplasm. // Microfilaments, intermediate filaments, and microtubules that provide support and movement for eukaryotic cytoplasm. // System of protein filaments in the cytoplasm of a eukaryotic cell that gives the cell shape and the capacity for directed movement. Its most abundant components are actin filaments, microtubules, and intermediate filaments. // The internal scaffolding that gives a cell its characteristic shape; consists of microtubules, neurofilaments, and microfilaments. cytosol The watery fluid inside a cell. // The intracellular structural network composed of actin filaments, microtubules, and intermediate filaments. // The network of filamentous protein structures along which vesicles and organelles are moved and which are ultimately required for cell shaping.

Answer 19

The continuous aqueous phase of the cytoplasm, with its dissolved solutes; excludes the organelles such as mitochondria. // Contents of the main compartment of the cytoplasm, excluding membrane-bounded organelles such as endoplasmic reticulum and mitochondria. // One of several major compartments within cells containing elements such as the cytoskeleton, and mitochondria, and separated by membranes from distinct compartments such as the nucleus and vesicular system. // The fluid portion of cytoplasm. // The viscous, syruplike fluid medium with dissolved solutes in the cytoplasm.

Answer 20

The enzymatic removal of amino groups from biomolecules such as amino acids or nucleotides. // Process of removing the amine group of an amino acid. // The removal of an amino group from an amino acid to form ammonia. See also ammonification. // The removal of amino groups from compounds, particularly amino acids, with the production of urea. // The removal of an amino group from a molecule, as occurs with amino acids during metabolic degradation. // Destruction of a protein’s or nucleic acid’s higher-order structure. // Loss of native configuration of a macromolecule, usually accompanied by loss of biological activity. Denatured proteins often unfold their polypeptide chains and express changed properties of solubility. // Partial or complete unfolding of the specific native conformation of a polypeptide chain, protein, or nucleic acid such that the function of the molecule is lost. // A change in a protein’s complex three-dimensional shape that causes its biological activity to be impaired or to cease; may occur with changes in pH or increased temperature.// A change in the molecular structure of a protein, usually making it nonfunctional.

Answer 21

The nucleic acid of genetic material in all cells and some viruses. // A double-stranded molecule constructed from four nucleic acids that contains the genetic instructions for a cell. // Chemical carriers of a cell’s genetic information. // Polynucleotide formed from covalently linked deoxyribonucleotide units. The store of hereditary information within a cell and the carrier of this information from generation to generation. // The biopolymer consisting of deoxyribonucleotide units linked together through phosphate–sugar bonds. Found in the nucleus of cells, DNA contains an organism’s genetic information. // A doublestranded nucleic acid, composed of deoxyribonucleotide monomers; directs protein synthesis. // Deoxyribonucleic acid; the information-carrying genetic material that comprises the genes. DNA is a macromolecule composed of a long chain of deoxyribonucleotides joined by phosphodiester linkages. Each deoxyribonucleotide contains a phosphate group, the five-carbon sugar 2-deoxyribose, and a nitrogen-containing base. // Deoxyribonucleic acid, the biomolecule in cells that stores the genetic information; composed of 2 complementary nucleic acid strands bonded by G-C and A-T pairs. // Deoxyribonucleic acid; the genetic blueprint from which proteins are synthesized. A double-stranded helix of nucleotides. // A polynucleotide with a specific sequence of deoxyribonucleotide units covalently joined through 3’,5’-phosphodiester bonds; serves as the carrier of genetic information.

Answer 22

Process by which a cell undergoes a change to an overtly specialized cell type. // A process in which unspecialized cells develop characteristic structures and functions. // During embryonic development, the process by which structures become more complex and functionally specialized. // Process in which cells lose their omnipotence to adopt more specialized functions. // Specialization of cell structure and function during growth and development. // The process of dissecting skill into subunits and determining where errors are.

Answer 23

The net drift of molecules through space due to random thermal movements. // The net movement of molecules in the direction of lower concentration. // The net movement of molecules or ions from an area of higher concentration to an area of lower concentration. // Random movement of molecules or particles down their concentration gradient. // Movement of molecules through a domain, from an area of high concentration to one of low concentration, by random molecular movement. // The process by which gas molecules spread out in response to a concentration gradient. // The temperature-dependent movement of molecules from regions of high concentration to regions of low concentration, resulting in a more even distribution.

Answer 24

A carbohydrate consisting of two covalently joined monosaccharide units. // Carbohydrate composed of two monosaccharides; e.g., sucrose. // A carbohydrate composed of two monosaccharides. // A sugar consisting of two simple sugars, or monosaccharides. // A carbohydrate formed by linking two simple sugars through an acetal bond. // Carbohydrate molecule composed of two monosaccharides linked by a chemical bond. distal convoluted tubule (DCT) The part of the renal nephron between the loop of Henle and the collecting duct system.

Answer 25

An enzyme that catalyzes template-dependent synthesis of DNA from its deoxyribonucleoside 5’-triphosphate precursors. // Enzyme that synthesizes DNA by copying a DNA template. // An enzyme that catalyzes the synthesis of DNA. // Enzyme that synthesizes DNA by joining nucleotides together using a DNA template as a guide. // DNA-synthesizing enzymes.

Answer 26

Localized swelling of a tissue. // Swelling caused by the entry of fluid and cells from the blood into the tissues; it is one of the cardinal features of inflammation. // Abnormal fluid accumulation in the interstitial tissue spaces. // An abnormal accumulation of interstitial fluid in tissues, causing swelling. // Swelling of interstitial spaces with fluid that results in excess of accumulation of water in the tissues.

Answer 27

Movement of charged solutes in response to an electrical field; often used to separate mixtures of ions, proteins, or nucleic acids. // The migration of suspended particles in an electric field. // A technique used for separating charged organic molecules, particularly proteins and DNA fragments. The mixture to be separated is placed on a buffered gel or paper, and an electric potential is applied across the ends of the apparatus. Negatively charged molecules migrate toward the positive electrode, and positively charged molecules migrate toward the negative electrode. // Separation of molecules in an electrical field. // Separation technique based on the mobility of analytes in an electric field. Important techniques are one- and two-dimensional gel electrophoresis and capillary electrophoresis.

Answer 28

A reaction that has a positive freeenergy change and is therefore nonspontaneous. In an energy diagram, the product of an endergonic reaction has a higher energy level than the reactants. // A chemical reaction that consumes energy (that is, for which DG is positive). // A chemical reaction that requires energy. // Reaction with positive ΔG. // Chemical reaction that requires the input of energy.

Answer 29

Movement of substances from the extracellular environment into the cell through the formation of a vesicle. // The process by which material is moved into a eukaryotic cell. // The uptake of extracellular material by its inclusion in a vesicle (endosome) formed by invagination of the plasma membrane. // Uptake of material into a cell by an invagination of the plasma membrane and its internalization in a membraneenclosed vesicle. See also pinocytosis and phagocytosis. endoderm Embryonic tissue that is the precursor of the gut and associated organs. // Cellular uptake of soluble macromolecules or particles through an endocytic vesicle. // The process by which a bit of the cell membrane is pinched off, internalized, and converted to an intracellular vesicle. See also exocytosis.

Answer 30

An extensive system of double membranes in the cytoplasm of eukaryotic cells; it encloses secretory channels and is often studded with ribosomes (rough endoplasmic reticulum). // Cellular endomembrane system in which proteins are modified posttranslationally. // Membranous portion of a cell where protein synthesis and lipid synthesis occur. // Network of membranes in the cytoplasm to which ribosomes adhere. // A membranous network in eukaryotic cells connecting the plasma membrane with the nuclear membrane. // Labyrinthine membranebounded compartment in the cytoplasm of eukaryotic cells, where lipids are synthesized and membrane-bound proteins and secretory proteins are made. // Organelle composed of an extensive network of connected membranes; involved in synthesis, transport, and storage of macromolecules, and detoxification of drugs: present as smooth ER or rough ER.

Answer 31

A biomolecule, either protein or RNA, that catalyzes a specific chemical reaction. It does not affect the equilibrium of the catalyzed reaction; it enhances the rate of the reaction by providing a reaction path with a lower activation energy. // Protein that catalyzes a chemical reaction by lowering the activation energy. // A biochemical catalyst made of protein that increases the rates of biochemical reactions. // A biological catalyst. Enzymes are large proteins that catalyze specific biochemical reactions. // A molecule that catalyzes biochemical reactions in a living organism, usually a protein. See also ribozyme. // A protein compound that speeds a chemical reaction. // A protein that accelerates a specific chemical reaction in a living system. // A protein that facilitates a biochemical reaction by lowering the energy required. // Protein that catalyses a chemical reaction, e.g., the hydrolysis of acetylcholine. // Protein that catalyzes a specific chemical reaction.

Answer 32

A unicellular or multicellular organism with cells having a membranebounded nucleus, multiple chromosomes, and internal organelles. // A cell having DNA inside a distinct membrane-enclosed nucleus. // A member of the large group of organisms that have nuclei enclosed by a membrane within their cells (cf. Prokaryote). // Organism composed of one or more cells that have a distinct nucleus. Member of one of the three main divisions of the living world, the other two being bacteria and archaea. // Cells with a membrane-bounded nucleus.

Answer 33

A reaction that has a negative freeenergy change and is therefore spontaneous. On an energy diagram, the product of an exergonic reaction has a lower energy level than that of the reactants. // A chemical reaction that proceeds with the release of free energy (that is, for which DG is negative). // A chemical reaction that releases energy. // Chemical reaction in which chemical energy is released. // Reaction with negative ΔG.

Answer 34

Process whereby contents within a vesicle are exported outside a cell. // Excretion of material from the cell by vesicle fusion with the plasma membrane; can occur constitutively or be regulated. // Secretion of water-soluble substances by fusion of an exocytic vesicle with the plasma membrane. // The fusion of an intracellular vesicle with the plasma membrane, releasing the vesicle contents to the extracellular space. // The process whereby material is released from an intracellular vesicle into the extracellular space by fusion of the vesicle membrane with the cell membrane. See also endocytosis.

Answer 35

The segment of a eukaryotic gene that encodes a portion of the final product of the gene; a segment of RNA that remains after posttranscriptional processing and is transcribed into a protein or incorporated into the structure of an RNA. See also intron. // A portion of a DNA molecule that codes for a section of the future messenger RNA molecule; these “coding” regions in pre-messenger RNA are joined together to form mature messenger RNA. // Segment of a eukaryotic gene that consists of a sequence of nucleotides that will be represented in mRNA or in a final transfer, ribosomal, or other mature RNA molecule. In protein-coding genes, exons encode the amino acids in the protein. An exon is usually adjacent to a noncoding DNA segment called an intron. // A region of a eukaryotic chromosome that encodes a protein. // A section of DNA that contains genetic information. // Blocks of noncontiguous coding sequences (generally short) present in many cellular and viral pre-mRNAs. (Chapter 10) // The portion of RNA transcribed from the DNA that is translated into a protein. // The parts of the gene that are represented in the mature RNA. // The segments of a eukaryotic gene that correspond to the sequences in the final processed RNA transcript of that gene.

Answer 36

Inhibition of a metabolic pathway by its end product. // Inhibition of an allosteric enzyme at the beginning of a metabolic sequence by the end product of the sequence; also known as end-product inhibition. // Inhibition of an enzyme in a particular pathway by the accumulation of the end-product of the pathway; also called endproduct inhibition. // The process in which a product of a reaction feeds back to inhibit a previous reaction in the same pathway. // The accumulated end product of a biochemical pathway stops synthesis of that product. A late metabolite of a synthetic pathway regulates synthesis at an earlier step of the pathway.

Answer 37

(flă-jel′-ŭm; pl., flagella, -ă) Whiplike locomotory extension of the plasma membrane; enables a sperm cell to move. // A cell appendage used in propulsion. Bacterial flagella have a much simpler structure than eukaryotic flagella, which are similar to cilia. // A whiplike organelle of locomotion in certain cells; locomotor structures in flagellate protozoa. // Long, whiplike protrusion whose undulations drive a cell through a fluid medium. Eukaryotic flagella are longer versions of cilia. Bacterial flagella are smaller and completely different in construction and mechanism of action. Compare cilium. // A thin appendage from the surface of a cell; used for cellular locomotion; composed of flagellin in prokaryotic cells, composed of 9 + 2 microtubules in eukaryotic cells.

Answer 38

Specific protein that acquires its energy from guanosine triphosphate; when activated by a membrane receptor, it relays the signal to another membrane protein and alters the activity of that protein. // A trimeric GTPbinding protein with intrinsic GTPase activity that couples GPCRs to enzymes or ion channels in the plasma membrane. // A large family of GTP-binding proteins that act in intracellular signaling pathways and in membrane trafficking. Active when GTP is bound, they self-inactivate by converting GTP to GDP. Also called guanosine nucleotide–binding proteins. // Intracellular GTPases that act as molecular switches in signaling pathways. They bind GTP to induce their active conformation, which is lost when GTO is hydrolyzed to GDP. There are two kinds of G proteins: the heterotrimeric (α, β, γ subunits) receptor-associated G proteins, and the small G proteins, such as Ras and Raf, which act downstream of many transmembrane signaling events. // GTP-binding signal transducing proteins that mediate most hormone effects. // A membrane-enclosed protein that binds guanosine triphosphate (GTP) when activated by a membrane receptor. Active G-proteins can stimulate or inhibit other membrane-enclosed proteins.

Answer 39

A chromosomal segment that codes for a single functional polypeptide chain or RNA molecule. // A hereditary determinant of a specific biological function; a unit of inheritance (DNA) located in a fixed position on a chromosome; a segment of DNA encoding one polypeptide and defined operationally by the cis-trans or complementation test. // A length of DNA directing the synthesis of a polypeptide or a functional RNA. // A segment of DNA (a sequence of nucleotides in DNA) encoding a functional product. // A portion of DNA that encodes for a specific protein. // A sequence of codons within a DNA molecule that codes for a single protein. // A unit of heredity; a sequence of DNA that encodes a single polypeptide or protein. // Region of DNA that is transcribed as a single unit and carries information for a discrete hereditary characteristic, usually corresponding to (1) a single protein (or set of related proteins generated by variant post-transcriptional processing), or (2) a single RNA (or set of closely related RNAs). // Segment of DNA containing information to direct synthesis of a specific protein; functional unit of DNA.

Answer 40

One complete copy of the genetic information in a cell. // The totality of genetic information belonging to a cell or an organism; in particular, the DNA that carries this information. // A complete set (n) of chromosomes (hence, of genes) inherited as a unit from one parent. // All the genetic information encoded in a cell or virus. // The entirety of genetic information of an organism necessary for its development and functioning. This information is encoded in deoxyribonucleic acid (DNA). // The total content of an organism’s genetic material.

Answer 41

The genetic constitution of an individual that, along with environmental influences, contributes to the phenotype. // The genetic constitution of an organism, as distinct from its physical characteristics, or phenotype. // Genetic constitution of an individual cell or organism. The particular combination of alleles found in a specific individual. // The genetic constitution (gene makeup) of an organism (cf. Phenotype). // The genetic makeup of an animal or person. // The genetic makeup of an organism.

Answer 42

Polysaccharide formed from glucose monomers. // A highly branched form of starch. // A storage form of carbohydrate that is found in the skeletal muscle and liver. // Carbohydrate storage molecule consisting of branching chains of glucose. // Polysaccharide composed exclusively of glucose units. Used to store energy in animal cells. Large granules of glycogen are especially abundant in liver and muscle cells.

Answer 43

A lipid containing a carbohydrate group. // Lipid with an attached carbohydrate. // A biological molecule in which a carbo hydrate is linked through a glycoside bond to a lipid. // A triglyceride composed of a fatty acid, a hydrocarbon chain, and a sugar molecule as the polar section. // Carbohydrate-containing lipid. // Lipid molecule with a sugar residue or oligosaccharide attached.

Answer 44

First stage of cellular respiration in which glucose is partially catabolized to form pyruvate and transfer energy to form ATP molecules. // A series of ten enzyme-catalyzed reactions that break down glucose into 2 equivalents of pyruvate, CH3COCO2⁻. // The breakdown of glucose to pyruvate in a cell in the absence of oxygen. // The catabolic pathway by which a molecule of glucose is broken down into two molecules of pyruvate. // The main pathway for the oxidation of glucose to pyruvic acid; also called Embden-Meyerhof pathway. // Ubiquitous metabolic pathway in the cytosol in which sugars are incompletely degraded with production of ATP. Literally, “sugar splitting.”

Answer 45

A protein containing a carbohydrate group. // A biological molecule in which a carbohydrate is linked through a glycoside bond to a protein. // A protein carrying covalently linked sugar chains (oligosaccharides). // A protein containing covalently bound carbohydrate. // Any protein with one or more saccharide or oligosaccharide chains covalently linked to amino acid side chains. Most secreted proteins and most proteins exposed on the outer surface of the plasma membrane are glycoproteins.

Answer 46

An organelle that sorts and chemically modifies proteins that are destined for delivery to different parts of the cell. // Cellular organelle that packages macromolecules, such as lipids and proteins destined to become part of plasma membrane or released from the cell. // Series of saclike membranes that act as a center to package, sort, and modify molecules arriving from the endoplasmic reticulum in a transport vesicle. // Complex organelle in eukaryotic cells, centered on a stack of flattened, membraneenclosed spaces, in which proteins and lipids transferred from the endoplasmic reticulum are modified and sorted. It is the site of synthesis of many cell wall polysaccharides in plants and extracellular matrix glycosaminoglycans in animal cells. // An organelle involved in the secretion of certain proteins. // A complex membranous organelle of eukaryotic cells; functions in the posttranslational modification of proteins and their secretion from the cell or incorporation into the plasma membrane or organellar membranes. // A membranous system within cells that is involved in the secretion of cellular substances.

Answer 47

The time required for decay of a molecule or macromolecule to half of the original concentration. // The time required for the disappearance or decay of one-half of a given component in a system. // The time that it takes for half of the substrate molecules to react in a first-order reaction. // Time required to reduce substance by one-half of its original quantity. // The time required for the concentration of a reactant or the amount of a radioactive isotope to fall to one-half of its initial value.

Answer 48

The iron-containing compound in blood that binds oxygen. // A heme protein in erythrocytes; functions in oxygen transport. // Conjugated protein compound containing iron, located in erythrocytes of vertebrates; important in the transportation of oxygen to the cells of the body. // A red-pigmented protein that transports oxygen and carbon dioxide; responsible for characteristic red color of blood. // The iron-containing pigment within red blood cells that binds oxygen for efficient transport.

Answer 49

A protein associated with DNA in eukaryotic chromosomes. // Conserved group of proteins that bind to negatively charged DNA and are part of the nucleosome. Modification of histone proteins are important for epigenetic regulation. // One of a group of small abundant proteins, rich in arginine and lysine, that combine to form the nucleosome cores around which DNA is wrapped in eukaryotic chromosomes. // Group of proteins rich in basic amino acids. They function in the coiling of DNA in chromosomes and in the regulation of gene activity. // Small, basic proteins that are tightly associated with DNA in chromatin. // The family of basic proteins that associate tightly with DNA in the chromosomes of all eukaryotic cells.

Answer 50

An organic product of cells of one part of the body that is transported by the body fluids to another part where it influences activity or serves as a coordinating agent. // Signal molecule secreted by an endocrine cell into the bloodstream, which can then carry the signal to distant target cells. // Chemical formed by an endocrine gland and transported by the blood to its target organ to alter cellular activity. // A chemical produced by one part of the body that has a biochemical effect on a different part of the body. // A chemical substance synthesized in small amounts by an endocrine tissue and carried in the blood to another tissue, where it acts as a messenger to regulate the function of the target tissue or organ. // Chemical messengers that are secreted by an endocrine gland and carried through the bloodstream to a target tissue.

Answer 51

A weak electrostatic attraction between one electronegative atom (such as oxygen or nitrogen) and a hydrogen atom covalently linked to a second electronegative atom. // Dipole-dipole interaction involving a hydrogen atom. // Noncovalent bond in which an electropositive hydrogen atom is partially shared by two electronegative atoms. // A bond between a hydrogen atom covalently bonded to oxygen or nitrogen and another covalently bonded oxygen or nitrogen atom. // A strong attraction between the H atom on one molecule and the F, O, or N on its neighbor. // A weak attraction between a hydrogen atom bonded to an electronegative atom and an electron lone pair on another electronegative atom. // A weak attraction formed between a partially positive hydrogen atom within a polar molecule and a partially negative atom (e.g., oxygen) within a polar molecule. // Weak interactions between electronegative atoms and hydrogen atoms (electropositive) that are linked to other electronegative atoms.

Answer 52

Chemical reaction in which water is used during the breakdown of a complex molecule. // Cleavage of a bond, such as an anhydride or peptide bond, by the addition of the elements of water, yielding two or more products. // The splitting of a chemical bond with water, resulting in the addition of H and OH to the products. // A decomposition reaction in which chemicals react with the H+ and OH- of a water molecule. // Cleavage of a bond by the addition of water.

Answer 53

Decreased oxygen level. // The metabolic condition in which the supply of oxygen is severely limited. // A physiological condition caused by low levels of oxygen, marked by dizziness, headache, shortness of breath, and eventually unconsciousness or even death in severe cases. // Metabolic state of insufficient oxygen supply to cells, tissues, or organisms that usually rely on oxygenic metabolism. Hypoxia induces fermentative metabolism and specific gene expression changes andmay cause death in sensitive organisms. // Oxygen deficiency.

Answer 54

A general term for the elaborate response that leads to local accumulation of white blood cells and fl uid; initiated by local infection or tissue damage; many diff erent forms of this response, characterized by the degrees of tissue damage, capillary leakage, and immune cell infi ltration, occur aft er infection with pathogens. // A host response to tissue damage characterized by redness, pain, heat, and swelling; and sometimes loss of function. // A local cellular response that is marked by leukocytic infiltration, pain, swelling, and often loss of function. // A natural protective response of tissues to harmful stimuli. The cardinal signs of inflammation in skin include heat, redness, swelling, and pain. // A nonspecific, localized response of innate immunity to tissue injury.

Answer 55

A portion of DNA that lies between two exons; noncoding regions in premessenger RNA. These are removed during pre-messenger RNA processing. // A region in a eukaryotic gene that does not code for a protein or mRNA. // A section of DNA that does not contain genetic information. // A sequence of nucleotides in a gene that is transcribed but excised before the gene is translated; also called intervening sequence. See also exon. // Noncoding region of a eukaryotic gene that is transcribed into an RNA molecule but is then excised by RNA splicing during production of the mRNA or other functional RNA. // The portion of RNA transcribed from the DNA that is not eventually translated into a protein. Sometimes called junk RNA. // Intervening sequences of DNA bases within eukaryotic genes that are not represented in the mature RNA transcript because they are spliced out of the primary RNA transcript. // Noncoding sequences that separate coding sequences (exons) in many cellular and viral pre-mRNAs. // The parts of a gene that do not appear in the mature, functional RNA product.

Answer 56

Membrane protein that can form watercontaining pores so that mineral ions can enter or leave cells. // A membrane-spanning protein that forms a pore that allows the passage of ions from one side of the membrane to the other. // A pore in the membrane that is selectively permeable for specific ions. // An integral protein that provides for the regulated transport of a specific ion, or ions, across a membrane. // Transmembrane protein complex that forms a water-filled channel across the lipid bilayer through which specific inorganic ions can diffuse down their electrochemical gradients.

Answer 57

A chemical bond formed when atoms gain or lose electrons in the outer energy levels. // A chemical bond formed between two oppositely charged ions, generally a metallic cation and a nonmetallic anion, that are attracted to each other by electrostatic forces. // Chemical bond formed when a cation is electrostatically attracted to an anion. // The electrostatic attraction between ions of unlike charge. // Attractions between oppositely charged chemical groups.

Answer 58

Molecules composed of the same number and types of atoms but with a different arrangement; e.g., glucose and galactose. // One or two molecules with the same chemical formula but different structures. // Any two molecules with the same molecular formula but a different arrangement of molecular groups. // Alternative molecular forms with identical composition. // Compounds that have the same molecular formula but different structures.

Answer 59

One of the two newly synthesized strands of DNA found at a replication fork. The lagging strand is made in discontinuous lengths that are later joined covalently. // The complement of the original 3’ → 5’ DNA strand that is synthesized discontinuously in small pieces that are subsequently linked by DNA ligases. // The DNA strand that, during replication, must be synthesized in the direction opposite to that in which the replication fork moves. // The strand of DNA that is synthesized discontinuously during replication. // The strand that is synthesized piecemeal during DNA replication.

Answer 60

A protein that binds a carbohydrate, commonly an oligosaccharide, with very high affinity and specificity, mediating cell-cell interactions. // A carbohydrate-binding protein. // A protein that binds to a specific sugar. // Carbohydrate-binding proteins on a cell, not an antibody. // Protein that binds tightly to a specific sugar. Abundant lectins from plant seeds are used as affinity reagents to purify glycoproteins or to detect them on the surface of cells.

Answer 61

Any one of several types of white blood cells. // A white blood cell. Leukocytes include lymphocytes, polymorphonuclear leukocytes, and monocytes. // General name for all the nucleated blood cells lacking hemoglobin. Also called white blood cells. Includes lymphocytes, granulocytes, and monocytes. // White blood cell; involved in the immune response in mammals. // White blood cell; part of the immune system that fights infections. // General name for all the nucleated blood cells lacking hemoglobin. Also called leukocytes. Includes lymphocytes, granulocytes, and monocytes.

Answer 62

Chemical released from one cell that binds to receptors on another cell; e.g., hormone, neurotransmitter. // A small molecule that binds noncovalently to a protein. // A small molecule that binds specifically to a larger one; for example, a hormone is the ligand for its specific protein receptor. // A molecule that can bind to another molecule in or on cells. // A neutral molecule or an ion that acts as a Lewis base with the central metal ion in a complex ion. // Any molecule that binds to a specific site on a protein or other molecule. From Latin ligare, to bind. // Substance that binds to a receptor in a specific way like a key in a lock.

Answer 63

A member of the class of biochemical compounds that are insoluble in water but soluble in nonpolar solvents, including fatty acids, triglycerides, and steroids. // A molecule composed of fatty acids and triglycerides. // A non–water-soluble organic molecule, including triglycerides, phospholipids, and sterols. // A small water-insoluble biomolecule generally containing fatty acids, sterols, or isoprenoid compounds. // Group of hydrophobic macromolecules including triglycerides, phospholipids, steroids, and eicosanoids. // Naturally occurring substances isolated from cells and tissues by extraction with a nonpolar solvent. Lipids belong to many different structural classes, including fats, terpenoids, prostaglandins, and steroids. // Substances with strong hydrophobic properties.

Answer 64

White blood cell involved in immune responses (i.e., T-lymphocyte, B-lymphocyte). // A class of white blood cells that bear variable cell-surface receptors for antigen and are responsible for adaptive immune responses. There are two main types—B lymphocytes (B cells) and T lymphocytes (T cells)—which mediate humoral and cell-mediated immunity, respectively. On antigen recognition, a lymphocyte enlarges to form a lymphoblast and then proliferates and differentiates into an antigen-specific effector cell. // A general class of white blood cells that are important components of the immune system of vertebrate animals. // A leukocyte involved in specific immune responses. // White blood cell responsible for the specificity of adaptive immune responses. Two main types: B cells, which produce antibody, and T cells, which interact directly with other effector cells of the immune system and with infected cells. T cells develop in the thymus and are responsible for cell-mediated immunity. B cells develop in the bone marrow in mammals and are responsible for the production of circulating antibodies. // A subclass of leukocytes involved in the immune response. See also B lymphocytes; T lymphocytes.

Answer 65

Organelle containing digestive enzymes. // A membrane-bounded organelle of eukaryotic cells; it contains many hydrolytic enzymes and serves as a degrading and recycling center for unneeded components. // A small, membrane-bound cellular organelle that contains enzymes dedicated to the degradation of macromolecules. // A vesicle in the cell that contains enzymes that degrade sugars, proteins, nucleic acids, and lipids. // An organelle containing digestive enzymes. // Membrane-enclosed organelle in eukaryotic cells containing digestive enzymes, which are typically most active at the acid pH found in the lumen of lysosomes. // Structure of a cell that contains digestive enzymes. // Enzyme that attacks the bacterial cell wall. Present in saliva, tears, sweat, and nasal secretions. // An enzyme that cleaves the peptidoglycan in bacterial cell walls. // Enzyme that catalyzes the cutting of polysaccharide chains in the cell walls of bacteria. // An enzyme capable of hydrolyzing bacterial cell walls. // Antimicrobial enzyme that degrades bacterial cell walls.

Answer 66

A large molecule; term used to identify molecules of proteins and nucleic acids. // A large organic molecule. // A molecule having a molecular weight in the range of a few thousand to many millions. // Polymers constructed of long chains of covalently linked, small organic (carbon-containing) molecules. The principal building blocks from which a cell is constructed and the components that confer the most distinctive properties of living things. // Large organic molecules; e.g., carbohydrates, nucleic acids, proteins.

Answer 67

(me-dūl′ă) Inner region of an organ; e.g., adrenal medulla. // The central or collecting point of an organ. The thymic medulla is the central area of each thymic lobe, rich in bone marrow-derived antigen-presenting cells and the cells of a distinctive medullary epithelium. The medulla of the lymph node is a site of macrophage and plasma cell concentration through which the lymph flows on its way to the efferent lymphatics. // A lichen body consisting of algae (or cyanobacteria) and fungi. // (ob-long-gah′tă) Brainstem region that transmits information between the spinal cord and higher brain centers; controls heart rate, blood pressure, breathing. // The part of the hindbrain caudal to the pons and cerebellum; also called medulla.

Answer 68

A long-lived B or T cell responsible for the memory, or secondary, response. // In immunology: a T or B lymphocyte generated following antigen stimulation that is more easily and more quickly induced to become an effector cell or another memory cell by a later encounter with the same antigen. // A subset of B and T lymphocytes maintained aft er each encounter with a foreign antigen; these cells survive for years and are ready to respond and proliferate upon subsequent encounter with the same antigen. // B and T lymphocytes that mediate immunological memory. They are more sensitive than naive lymphocytes to antigen and respond rapidly on reexposure to the antigen that originally induced them. // Lymphocytes that produce a strong, rapid response during the second exposure to an invader.

Answer 69

A class of RNA molecules, each of which is complementary to one strand of DNA; carries the genetic message from the chromosome to the ribosomes. // A kind of RNA formed by transcription of DNA and used to carry genetic messages from DNA to ribosomes. // A molecule constructed from four nucleic acids that carries the genetic instructions for the assembly of a protein from the nucleus to the cytoplasm. // RNA molecule that specifies the amino acid sequence of a protein. Produced in eukaryotes by processing of an RNA molecule made by RNA polymerase as a complementary copy of DNA. It is translated into protein in a process catalyzed by ribosomes. // RNA that carries information necessary for protein synthesis from the DNA to the ribosomes. // Specifies the amino acid sequence during protein synthesis. // The type of RNA molecule that directs the incorporation of amino acids into proteins.

Answer 70

All chemical reactions taking place in the body, including both anabolic and catabolic reactions. // The sum of all the chemical reactions that occur in a living cell. // A collective name for the many reactions that go on in the cells of living organisms. // Sum total of all chemical processes in living cells by which energy is provided and used. // The energy-releasing processes of cells, tissues, or the human body; may be measured in kilocalories expended. // The entire set of enzymecatalyzed transformations of organic molecules in living cells; the sum of anabolism and catabolism. // The sum of the anabolic and catabolic reactions occurring in the body. // The sum total of the chemical processes that take place in living cells. All of catabolism plus anabolism.

Answer 71

Hollow cylinders of tubulin protein that are part of the cytoskeleton; able to lengthen and shorten. // A hollow tube made of the protein tubulin; the structural unit of eukaryotic flagella and centrioles. // A polymer of the protein tubulin, forming a straight, hollow tube 20 nm in diameter. Microtubules, a component of the cytoskeleton, play an important role in axoplasmic transport. // Hollow filaments in the cytoplasm making up a part of the locomotor apparatus of a motile cell; component of the mitotic spindle. // Cytoskeletal fibers formed by the polymerization of tubulin. // Linear tubular structures of higher cells formed from tubulin dimers; essential for cell division and vesicular transport processes.

Answer 72

Important organelle for compartment of eukaryotic cells; site of the TCA cycle and respiration chain (production of ATP); mitochondria have their own DNA replication transcription and ribosomes. Originated from protobacteria. // Organelles in the cytoplasm of plant and animal cells where oxidative phosphorylation takes place to produce ATP. // Specialized cell organelles in which oxidative production of ATP occurs. // (pl., mitochondria, -ă) Organelle associated with the production of ATP during aerobic cellular respiration. // An organelle responsible for cellular respiration. Mitochondria generate adenosine triphosphate using the energy produced by the oxidation of food. // Membrane-bounded organelle of eukaryotic cells; contains the enzyme systems required for the citric acid cycle, fatty acid oxidation, electron transfer, and oxidative phosphorylation. // Unit of a cell that is responsible for the aerobic generation of energy in the form of ATP. // Membrane-bounded organelle, about the size of a bacterium, that carries out oxidative phosphorylation and produces most of the ATP in eukaryotic cells. // An organelle containing Krebs cycle enzymes and the electron transport chain.

Answer 73

Disjunction of duplicated chromosomes and division of the cytoplasm to produce two genetically identical daughter cells. // In eukaryotic cells, the multistep process that results in the replication of chromosomes and cell division. // The phase of the cell cycle in which newly duplicated chromosomes are distributed to two new daughter cells as a result of cell division. Also called M phase. // Process of somatic cell division. // A eukaryotic cell replication process in which the chromosomes are duplicated; usually followed by division of the cytoplasm of the cell. // Cell division.

Answer 74

Antibodies produced by a single clone of B lymphocytes, so that they are all identical. // Antibodies produced by a cloned hybridoma cell, which therefore are identical and directed against the same epitope of the antigen. (Hybridoma cells are stable antibody-producing cell lines that grow well in tissue culture; created by fusing an antibody-producing B cell with a myeloma cell.) // An antibody of a single specificity made by a clone of antibody-producing cells. // Antibody secreted by a hybridoma cell line. Because the hybridoma is generated by the fusion of a single B cell with a single tumor cell, each hybridoma produces antibodies that are all identical. // A specific antibody produced in vitro by a clone of B cells hybridized with cancerous cells.

Answer 75

A repeating unit in a polymer. // A single molecular entity that may combine with others to form more complex structures. // A small molecule that collectively combines to form polymers. // Identical or similar molecules that repeat within a polymer. // The simple starting units from which polymers are made.

Answer 76

The simplest carbohydrate molecules; e.g., glucose, ribose. // A carbohydrate consisting of a single sugar unit. // A simple sugar consisting of 3–7 carbon atoms. // The simplest carbohydrates, with three to eight carbon atoms and only one aldehyde or ketone group. // Polyalcohol containing a carbonyl group. // The simplest carbohydrate molecule. // Simple sugars.

Answer 77

An inheritable change in the nucleotide sequence of a chromosome. // Any change in the nitrogenous base sequence of DNA. // A change in the DNA at a particular locus in an organism. The term is used loosely to include point mutations involving a single gene change as well as a chromosomal change. // An alteration in a segment of DNA; may lead to production of an abnormal protein. // Heritable change in DNA structure. // Heritable change in the nucleotide sequence of a chromosome.

Answer 78

A unit of thick and thin filaments of muscle fibers. // Bundles of myofilaments within skeletal and cardiac muscle cells. // A cylindrical structure within a skeletal muscle fiber that contracts in response to an action potential. // Bundle of myofilaments forming an internal subdivision of skeletal and cardiac muscle. // Long, highly organized bundle of actin, myosin, and other proteins in the cytoplasm of muscle cells that contracts by a sliding filament mechanism.

Answer 79

A contractile protein; the major component of the thick filaments of muscle and other actin-myosin systems. // Type of motor protein that uses the energy of ATP hydrolysis to move along actin filaments. // A cytoskeletal protein in all cells and the major thick fi lament protein in a skeletal muscle fiber; causes muscle contraction by chemical interaction with actin. // The protein of the thick filaments in muscle. // Thick contractile protein of muscle tissue.

Answer 80

A cell of the nervous system that transmits electrical signals (e.g., action potential). // A cell of nervous tissue specialized for transmission of a nerve impulse. // A nerve cell. // The information-processing cell of the nervous system; also called nerve cell. Most neurons use action potentials to send signals over a distance, and all neurons communicate with one another using synaptic transmission. // Impulse-conducting cell of the nervous system, with extensive processes specialized to receive, conduct, and transmit signals.

Answer 81

A low molecular weight compound (usually containing nitrogen) secreted from the axon terminal of a neuron and bound by a specific receptor on the next neuron or on a myocyte; serves to transmit a nerve impulse. // Chemical released from a neuron that binds to receptors of another cell to initiate a cellular change. // Small signal molecule secreted by the presynaptic nerve cell at a chemical synapse to relay the signal to the postsynaptic cell. Examples include acetylcholine, glutamate, GABA, glycine, and many neuropeptides. // A chemical released by a presynaptic element upon stimulation that activates postsynaptic receptors. // Chemical produced by the body to transmit an electric signal to another cell type of structure in the body, usually across a synapse. // Signal compounds in the synapses of neurons that help convert an electric signal into a chemical response; important neurotransmitters are acetylcholine, noradrenaline, adrenaline, dopamine, serotonin, histamine, glycine, GABA, glutamate, endorphins, and several other peptides.

Answer 82

A base substitution in DNA that results in a nonsense codon. // A mutation that changes a codon specifying an amino acid to a termination codon. // A mutation that creates a stop codon. // A mutation that results in the premature termination of a polypeptide chain. // A substitution mutation that produces a translation termination codon.

Answer 83

A biological macromolecule composed of nucleotide monomers; DNA and RNA. // A macromolecule consisting of nucleotides; DNA and RNA are nucleic acids. // A biological polymer composed of nucleotide units that carries genetic information. // A macromolecule composed of phosphoric acid, pentose sugar, and organic bases; DNA and RNA. // Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA); biological polymers made of nucleotides joined together to form long chains. // Biologically occurring polynucleotides in which the nucleotide residues are linked in a specific sequence by phosphodiester bonds; DNA and RNA.

Answer 84

(pl., nucleoli) Spherical, dark body within the nucleus where subunits of ribosomes are made. // A prominent structure in the nucleus where rRNA is transcribed and ribosomal subunits are assembled. // An RNA-rich, spherical sack in the nucleus of metabolic cells; associated with the nucleolar organizer; storage place for ribosomes and ribosome precursors. // In eukaryotic cells, a densely staining structure in the nucleus; involved in rRNA synthesis and ribosome formation. // An area in a eukaryotic nucleus where rRNA is synthesized.

Answer 85

A compound consisting of a purine or pyrimidine base and a pentose sugar. // A structure formed from a pentose sugar and a base. // An organic compound consisting of a base covalently linked to ribose or deoxyribose. // A compound consisting of a purine or pyrimidine base covalently linked to a pentose. // A nucleic acid constituent consisting of a sugar residue bonded to a heterocyclic purine or pyrimidine base.

Answer 86

In eukaryotes, structural unit for packaging chromatin; consists of a DNA strand wound around a histone core. // Beadlike structure in eukaryotic chromatin, composed of a short length of DNA wrapped around an octameric core of histone proteins. The fundamental structural unit of chromatin. // The central unit of the chromatin. About 147 bp of DNA are wrapped around a histone octamer forming one nucleosome unit. // The structural unit of chromatin, formed from DNA and histones. // The nuclease-resistant subunit of chromatin that consists of about 146 nucleotides of DNA wrapped as 1.65 turns of negative superhelix around an octamer of histones—two molecules each of histones H2a, H2b, H3, and H4.

Answer 87

Building blocks of DNA and RNA; composed of a nitrogenous base, a phosphate group, and a sugar. // A compound consisting of a purine or pyrimidine base, a five- carbon sugar, and a phosphate. // A nucleoside phosphorylated at one of its pentose hydroxyl groups. // A structure formed from pentose sugar, base, and a variable number of phosphate groups. // A subunit of DNA and RNA molecules containing a phosphate group, a sugar, and a nitrogen-containing organic base. // Nucleoside with one or more phosphate groups joined in ester linkages to the sugar moiety. DNA and RNA are polymers of nucleotides. // The individual units composing nucleic acids; each consists of a phosphate group, a sugar, and a nitrogenous base. // Nucleic acid constituents consisting of a sugar residue bonded both to a hetero cyclic purine or pyrimidine base and to a phosphoric acid. Nucleotides are the monomer units from which DNA and RNA are constructed.

Answer 88

(1) The part of an atom consisting of the protons and neutrons. (2) The part of a eukaryotic cell that contains the genetic material. numerical identification Bacterial identification schemes in which test values are assigned a number. // Cellular structure housing DNA or a group of cell bodies in the central nervous system. // In eukaryotes, a membrane-bounded organelle that contains chromosomes. // (1) The roughly spherical organelle in a cell body containing the chromosomes. (2) A clearly distinguishable mass of neurons, usually deep in the brain. // The part of a eukaryotic cell that contains the chromosomes; separated from the cytoplasm by a membrane. // The very small, dense core of the atom that contains most of the atom’s mass and all of its positive charge; composed of protons and neutrons.

Answer 89

A gene encoding a protein that causes cellular transformation or tumorigenesis. // A gene that can cause cancerous transformation in animal cells growing in culture and tumor formation in animals themselves; a gene that promotes cell division. // A growth-promoting gene in cancer cells. // A cancer-causing gene; any of several mutant genes that cause cells to exhibit rapid, uncontrolled proliferation. See also proto-oncogene. // A gene that can bring about malignant transformation. // An altered gene whose product can act in a dominant fashion to help make a cell cancerous. Typically, an oncogene is a mutant form of a normal gene (proto-oncogene) involved in the control of cell growth or division.

Answer 90

An alternative name for enantiomers. Optical isomers are isomers that have a mirror-image relationship. // Two molecules that are nonsuperimposable mirror images of one another. // Stereoisomers that are nonsuperposable mirror images of each other. // Isomers that are mirror images. // Stereoisomers of a chiral substance that have a mirror-image relationship. Enantiomers have opposite conigurations at all chirality centers. // Two molecules that are nonsuperimposable mirror images of one another.

Answer 91

Complex, organized structures in the cytoplasm of a cell with unique characteristic shapes; called “little organs.” // Specialized part of a cell with a particular function or functions (for example, the cilium of a protozoan). // A membrane-enclosed structure inside a cell; examples are the nucleus, mitochondrion, endoplasmic reticulum, and Golgi apparatus. // A membrane-enclosed structure within eukaryotic cells. // A structure within a cell with a specialized function. // Subcellular compartment or large macromolecular complex, often membrane-enclosed, that has a distinct structure, composition, and function. Examples are nucleus, nucleolus, mitochondrion, Golgi apparatus, and centrosomes. // Membrane-bounded structures found in eukaryotic cells; contain enzymes and other components required for specialized cell functions.

Answer 92

The loss of electrons from a compound. // The loss of one or more electrons; also the gaining of oxygen or the loss of hydrogen. // Occurs when a chemical loses an electron. // A reaction that causes a decrease in electron ownership by carbon, either by bond formation between carbon and a more electronegative atom (usually oxygen, nitrogen, or a halogen) or by bond-breaking between carbon and a less electronegative atom (usually hydrogen). // The removal of electrons from a molecule. // Loss of electrons from an atom, as occurs during the addition of oxygen to a molecule or when a hydrogen is removed. Opposite of reduction.

Answer 93

A coupled reaction in which one substance is oxidized and one is reduced; also called redox reaction. // A reaction in which electrons are transferred from a donor to an acceptor molecule; also called a redox reaction. // Exchange reaction involving transfer of electrons from one chemical to another; also called a redox reaction. // Reactions in which electrons are transferred from one reactant to another and the oxidation states of certain atoms are changed. // Reaction in which one component becomes oxidized and the other reduced; an oxidation–reduction reaction. // Electron transfer reaction.

Answer 94

The enzymatic phosphorylation of ADP to ATP coupled to electron transfer from a substrate to molecular oxygen. // Process in bacteria and mitochondria in which ATP formation is driven by the transfer of electrons through the electron-transport chain to molecular oxygen. Involves the intermediate generation of an electrochemical proton gradient across a membrane and a chemiosmotic coupling of that gradient to the ATP synthase. // The synthesis of ATP coupled with electron transport. // Process of forming ATP by using coenzymes to transfer energy. // Process in bacteria and mitochondria in which ATP formation is driven by the transfer of electrons through the electron transport chain to molecular oxygen. Involves the intermediate generation of a proton gradient (pH gradient) across a membrane and a chemiosmotic coupling of that gradient to the ATP synthase.

Answer 95

Diseasecausing substance or organism. // Disease-causing virus or microorganism. // Microorganism that typically causes disease when it infects a host. // A disease-causing organism. // An organism that causes a disease. // An organism, cell, virus, or prion that causes disease.

Answer 96

The bond that forms between the amine end of one amino acid and the carboxylic end of another. // A bond joining the amino group of one amino acid to the carboxyl group of a second amino acid with the loss of a water molecule. // A chemical bond holding amino acid subunits together in proteins. // A substituted amide linkage between the -amino group of one amino acid and the -carboxyl group of another, with the elimination of the elements of water. // Amide bond between two amino acids. // An amide bond in a peptide chain. // The covalent bond between the amino group of one amino acid and the carboxyl group of another. // Chemical bond joining amino acid monomers.

Answer 97

Membrane-bound organelle containing oxidative enzymes. // Membrane-bounded organelle of eukaryotic cells; contains peroxide-forming and peroxide-destroying enzymes. // Organelle that oxidizes amino acids, fatty acids, and alcohol. // A subcellular organelle that contains enzymes involved in the degradation of fatty acids and amino acids. // Small membrane-bounded organelle that uses molecular oxygen to oxidize organic molecules. Contains some enzymes that produce and others that degrade hydrogen peroxide (H2O2). // Structure of cells that facilitates the metabolism of fatty acids and various toxins. // Catalase-rich organelles that contain oxidative enzymes.

Answer 98

“Cell eating”; the cellular uptake of a solid particle. // A form of endocytosis by which cells ingest and digest solid substances; “cell eating.” // The internalization of particulate matter by cells by a process of engulfment, in which the cell membrane surrounds the material, eventually forming an intracellular vesicle (phagosome) containing the ingested material. // Engulfment of dying cellular debris and virus particles by myeloid cells, including dendritic cells. // Process by which unwanted cells, debris, and other bulky particulate material is endocytosed (“eaten”) by a cell. Prominent in carnivorous cells, such as Amoeba proteus, and in vertebrate macrophages and neutrophils. From Greek phagein, to eat. // The ingestion of particles by eukaryotic cells.

Answer 99

Observable characteristics of an individual. // The external manifestations of an organism’s genotype, or genetic makeup. // The observable character (including both physical appearance and behavior) of a cell or organism. // The observable characteristics of an organism.

Answer 100

Lipid that forms bilayers of the plasma membrane. // A complex lipid composed of glycerol, two fatty acids, and a phosphate group. // A lipid containing one or more phosphate groups. // A lipid in which two fatty acids are bound to carbons 1 and 2 of a glycerol molecule and a phosphate moiety is bound to the third carbon. // Compound similar in structure to a triglyceride but in which one fatty acid is replaced by a phosphate group. // The main category of lipids used to construct biomembranes. Generally composed of two fatty acids linked through glycerol (or sphingosine) phosphate to one of a variety of polar groups. // Lipids that contain a phosphate residue. For example, glycerophospholipids contain a glycerol backbone linked to two fatty acids and a phosphoric acid. // Lipids with phosphate in their hydrophilic head group.

Answer 101

Formation of a phosphate derivative of a biomolecule, usually by enzymatic transfer of a phosphoryl group from ATP. // Process of adding a phosphate group to a molecule. // Reaction in which a phosphate group is covalently coupled to another molecule. // The addition of a phosphate group to an organic molecule. // A biochemical reaction in which a phosphate group (PO₄²⁻) is transferred from adenosine triphosphate (ATP) to another molecule. Phosphorylation of proteins by protein kinases changes their biological activity. // Addition of a phosphate group to a molecule, usually a protein, catalyzed by enzymes called kinases.

Answer 102

A cell that an activated B cell differentiates into; plasma cells manufacture specific antibodies. // Cell that produces and releases specific antibodies; derived from B-lymphocytes. // Antibody-producing white blood cells derived from B lymphocytes. // Immunoglobulin-producing cells in blood and lymphatic tissues. // Mature B cells that synthesize secreted antibodies. // Terminally differentiated activated B lymphocytes. Plasma cells are the main antibody-secreting cells of the body. They are found in the medulla of the lymph nodes, in splenic red pulp, in bone marrow, and in mucosal tissues.

Answer 103

A small circular DNA molecule that replicates independently of the chromosome. // An extrachromosomal hereditary determinant that exists in an autonomous state and is transferred independently of chromosomes. // An extrachromosomal, independently replicating, small circular DNA molecule; commonly employed in genetic engineering. // Circular, double-stranded DNAs that function as “accessory chromosomes” in bacteria. // A blood enzyme that is responsible for degrading the bloodclotting protein fibrin. // The principal fibrin-degrading enzyme.

Answer 104

Molecule composed of many repeating subunits (or monomers). // A molecule consisting of a sequence of similar molecules, or monomers. // A compound composed of many smaller subunits; results from the process of polymerization. // A large molecule made up of repeating smaller units. For example, polyethylene is a synthetic polymer made from repeating ethylene units, and DNA is a biopolymer made of repeating deoxyribonucleotide units. // A long chain-like molecule composed of repeating units called monomers. // Chemical compound made of small molecules arranged in a simple linear repeating structure to form a larger molecule.

Answer 105

A repetitive laboratory procedure that results in a geometric amplification of a specific DNA sequence. // A method for amplifying selected DNA sequences. // A procedure involving multiple cycles of denaturation, hybridization to oligonucleotide primers, and polynucleotide synthesis that amplifies a particular DNA sequence. // A technique using DNA polymerase to make multiple copies of a DNA template in vitro. See also cDNA. // Technique for amplifying specific regions of DNA by the use of sequence-specific primers and multiple cycles of DNA synthesis, each cycle being followed by a brief heat treatment to separate complementary strands. // A method for amplifying small amounts of DNA to produce larger amounts.

Answer 106

Applied to genes, variability at a gene locus in which all variants occur at a frequency greater than 1%. // Sequence variation in DNA. // The existence of two or more variants in a population of individuals, with at least two of the variants having frequencies greater than 1 percent. // The occurrence of multiple forms in the same population of a species. // Describes genome sequences that coexist as two or more sequence variants at high frequency in a population.

Answer 107

A long chain of amino acids linked by peptide bonds; the molecular weight is generally less than 10,000. // A chain of amino acids joined together by peptide bonds. // (1) A chain of amino acids. (2) A group of antibiotics. // Chain of amino acids linked by peptide bonds. // A linear molecule with two or more amino acids and one or more peptide groups. They are called dipeptides, tripeptides, and so on, according to the number of amino acids present. // A string of amino acids held together by peptide bonds. // Linear polymer of amino acids. Proteins are large polypeptides, and the two terms can be used interchangeably. // Polymer of amino acids.

Answer 108

Class of carbohydrates composed of three or more monosaccharide monomers; e.g., glycogen. // A carbohydrate consisting of 8 or more monosaccharides joined through dehydration synthesis. // A linear or branched polymer of monosaccharide units linked by glycosidic bonds. // A long, chainlike molecule composed of many monosaccharide units bonded together. // Complex carbohydrate containing hundreds of monosaccharides; polysaccharides include starch, fiber, and glycosaminoglycans. // Polymer of monosaccharides. // A type of carbohydrate that is made of many simple sugars linked together by glycoside (acetal) bonds.

Answer 109

The covalent structure of a protein. // A description of the covalent backbone of a polymer (macromolecule), including the sequence of monomeric subunits and any interchain and intrachain covalent bonds. // Linear sequence of monomer units in a polymer, such as the amino acid sequence of a protein. // The amino acid sequence in a protein. // The sequence of amino acids composing a polypeptide linked together via peptide bonds. probiotic Live digestive tract bacteria that are beneficial to health. // The sequence of amino acids in a protein chain.

Answer 110

A cell whose genetic material is not enclosed in a nuclear envelope. // A term used historically to refer to any species in the kingdoms Bacteria and Archaea. The differences between bacteria (formerly referred to as “eubacteria”) and archaea are sufficiently great that the inclusive term is of marginal usefulness. A tendency to use “prokaryote” when referring only to bacteria is common and misleading; “prokaryote” also implies an ancestral relationship to eukaryotes, which is incorrect. In this text, “prokaryote” and “prokaryotic” are not used. // Single-celled microorganism whose cells lack a well-defined, membrane-enclosed nucleus. Either a bacterium or an archaeon. // A cellular organism without a nucleus.// A member of a large group of organisms (including bacteria and bluegreen algae) that lack true nuclei in their cells and that do not undergo mitosis.

Answer 111

A regulatory DNA sequence at the upstream end of a gene or an operon. // Nucleotide sequence in DNA to which RNA polymerase binds to begin transcription. // A DNA sequence at which RNA polymerase may bind, leading to initiation of transcription. // A nucleotide sequence to which RNA polymerase binds and initiates transcription; also, a chemical substance that enhances the transformation of benign cells into cancerous cells. // A region of DNA that binds RNA polymerase to initiate gene transcription. // A set of DNA sequences necessary for initiation of transcription by a DNA-dependent RNA polymerase. // The starting site on a DNA strand for transcription of RNA by RNA polymerase.

Answer 112

A hormonelike substance that is released by damaged cells, intensifies inflammation. // Local hormone derived from a fatty acid of the plasma membrane. // One of a class of polyunsaturated, cyclic lipids derived from arachidonate that act as paracrine hormones. // Lipid products of the metabolism of arachidonic acid that have a variety of effects on tissues, including activities as inflammatory mediators. // Lipids derived from arachidonic acid. Prostaglandins are present in nearly all body tissues and luids, where they serve many important hormonal functions.

Answer 113

Supramolecular assembly of enzymatic complexes that function in the degradation of damaged or unneeded cellular proteins. // A complex containing multiple proteases with different specificities that is responsible for degradation of polyubiquitin-tagged proteins to amino acids and small peptides. // A large intracellular multisubunit protease that degrades proteins, producing peptides. // A large protein complex containing peptidases and proteases that mediates the degradation of proteins into small peptides and amino acids. // A particle that destroys worn-out cellular proteins. // Large protein complex in the cytosol with proteolytic activity that is responsible for degrading proteins that have been marked for destruction by ubiquitylation or by some other means.

Answer 114

A large molecule containing carbon, hydrogen, oxygen, and nitrogen (and sulfur); some proteins have a helical structure and others are pleated sheets. // A macromolecule composed of one or more polypeptide chains, each with a characteristic sequence of amino acids linked by peptide bonds. // A macromolecule composed of one to several polypeptides. Each polypeptide consists of a chain of amino acids linked together by peptide bonds. // A polymer of amino acids strung together by peptide bonds. // Biological macromolecule composed of one or more chains of amino acid monomers. // The major macromolecular constituent of cells. A linear polymer of amino acids linked together by peptide bonds in a specific sequence. // Combinations of linked amino acids, all of which contain nitrogen. // Large peptides containing 50 or more amino acid residues. Proteins serve both as structural materials and as enzymes that control an organism’s chemistry.

Answer 115

Enzymes that digest proteins.

Answer 116

The full complement of proteins expressed in a given cell, or the complete complement of proteins that can be expressed by a given genome. // The total protein repertoire of a sample, such as a preparation of virus particles or a type of host cell. // The complete set of proteins encoded by a genome. // The entirety of proteins in an organism, a tissue, a cell, or a body fluid. // The totality of proteins made by a particular cell at a particular time.

Answer 117

A systematic investigation of the proteome including the global study of identity structure, quantity, and function of proteins. // Broadly, the study of the protein complement of a cell or organism. proteostasis The maintenance of a cellular steady-state collection of proteins that are required for cell functions under a given set of conditions. // Study of all the proteins, including all the covalently modified forms of each, produced by a cell, tissue, or organism. Proteomics often investigates changes in this larger set of proteins—in “the proteome”—caused by changes in the environment or by extracellular signals. // The science focused on determining the structures and functions of all the proteins produced by living organisms. // The science of determining all of the proteins expressed in a cell.

Answer 118

Three-dimensional relationship of the different polypeptide chains in a multisubunit protein or protein complex. // The highest level of protein structure, involving an ordered aggregation of individual proteins into a larger cluster. // The subunit interactions of an oligomeric protein. // The threedimensional structure of a multisubunit protein, particularly the manner in which the subunits fit together. // The way that subunits fit together in a multimeric protein.

Answer 119

An attachment for a pathogen on a host cell. // (1) A specialized protein that detects chemical signals, such as neurotransmitters, and initiates a cellular response. (2) A specialized cell that detects environmental stimuli and generates neural responses. // A cellular protein that causes physiological effects after binding an extracellular agent. // A molecule that can accept the binding of a ligand. // Any protein that binds a specific signal molecule (ligand) and initiates a response in the cell. Some are on the cell surface, while others are inside the cell. // Cellular protein that binds a ligand (e.g., hormone, neurotransmitter); also structure that detects a stimulus. // The cellular molecule to which a virus attaches to initiate infection.

Answer 120

The addition of electrons to a molecule. // The gain of electrons by a compound or ion. // The gaining of one or more electrons; also the gaining of hydrogen or the loss of oxygen. // A reaction that causes an increase of electron ownership by carbon, either by bond-breaking between carbon and a more electronegative atom or by bond formation between carbon and a less electronegative atom. // Occurs when a chemical gains an electron. // Addition of electrons to an atom, as occurs during the addition of hydrogen to a biological molecule or the removal of oxygen from it. Opposite of oxidation.

Answer 121

The sites of synthesis of nascent DNA chains that move away from origin as replication proceeds. // The Y-shaped structure generally found at the point where DNA is being synthesized. // The Y-shaped structure where the two parental strands of a DNA double helix are unwound and are being used as templates for the synthesis of new complementary strands. // Y-shaped region of a replicating DNA molecule at which the two strands of the DNA are being separated and the daughter strands are being formed. // The point of unraveling in a DNA chain where replication occurs.

Answer 122

A system of electron carriers in the inner mitochondrial membrane. // The electron-transfer chain; a sequence of electron-carrying proteins that transfers electrons from substrates to molecular oxygen in aerobic cells. // Electrontransport chain present in the inner mitochondrial membrane that generates an electrochemical gradient across the membrane that is used to drive ATP synthesis. // A series of enzymatic complexes associated with the inner membrane of the mitochondria and serving as the site of oxidative phosphorylation. // A series of compounds that transfer electrons from one compound to another, generating ATP by oxidative phosphorylation. // Series of reactions in which electron carrier molecules pass electrons “down the chain” from higher to successively lower energy levels. The energy released during such electron movement can be used to power various processes. Electron-transport chains present in the inner mitochondrial membrane (called the respiratory chain) and in the thylakoid membrane of chloroplasts generate a proton gradient across the membrane that is used to drive ATP synthesis. // The inal stage of catabolism in which ATP is produced.

Answer 123

A single-stranded RNA virus that uses the viral enzyme reverse transcriptase to transcribe its genome into a DNA intermediate that integrates into the host-cell genome to undergo viral replication. // An RNA virus containing a reverse transcriptase. // A type of virus that inserts a doublestranded DNA copy of its RNA genome into the host cell genome. //A virus that stores its genetic information in RNA and replicates by using reverse transcriptase to synthesize a DNA copy of its RNA genome. // RNA-containing virus that replicates in a cell by first making an RNA–DNA intermediate and then a double-strand DNA molecule that becomes integrated into the cell’s DNA. // The visual pigment, composed of the protein opsin and the chromophore retinal. // Seven-span membrane protein of the GPCR family that acts as a light sensor in rod photoreceptor cells in the vertebrate retina. Contains the light-sensitive prosthetic group retinol. // The light-sensing protein in retinal rod cells. // The photopigment in rod photoreceptors. // The pigment of the retina that forms photoreceptor cells. Sometimes called visual purple.

Answer 124

An enzyme that catalyzes the synthesis of DNA using an RNA template. // An RNA-directed DNA polymerase in retroviruses; capable of making DNA complementary to an RNA. // Enzyme first discovered in retroviruses that makes a double-strand DNA copy from a single-strand RNA template molecule. // Viral RNA-dependent DNA polymerase that is found in retroviruses and transcribes the viral genomic RNA into DNA during the life cycle of retroviruses (such as HIV). // An RNA-dependent DNA polymerase; an enzyme that synthesizes a complementary DNA from an RNA template. // Enzymes that transcribe RNA into a double-stranded DNA.

Answer 125

The bio polymer found in cells that serves to transcribe the genetic information found in DNA and uses that information to direct the synthesis of proteins. // The class of nucleic acids that comprises messenger RNA, ribosomal RNA, and transfer RNA. // Nucleic acid composed of ribonucleotide monomers; used to direct protein synthesis based on instructions in DNA; types include messenger RNA, ribosomal RNA, and transfer RNA. // Ribonucleic acid; the information-carrying material in some viruses; more generally, a molecule derived from DNA by transcription that may carry information (messenger or mRNA), provide subcellular structure (ribosomal or rRNA), transport amino acids (transfer or tRNA), or facilitate the biochemical modification of itself or other RNA molecules. // Ribonucleic acid. // A polyribonucleotide of a specific sequence linked by successive 3’,5’-phosphodiester bonds. // Nucleic acid that is similar to DNA but is single stranded. The three main types of RNA are ribosomal, transfer, and messenger RNA. // Polymer formed from covalently linked ribonucleotide monomers. See also messenger RNA, ribosomal RNA, transfer RNA.

Answer 126

A kind of RNA used in the physical makeup of ribosomes. // Any one of a number of specific RNA molecules that form part of the structure of a ribosome and participate in the synthesis of proteins. Often distinguished by their sedimentation coefficient (e.g., 28S rRNA, 5S rRNA). // The type of RNA molecule that forms ribosomes. // The RNA found in the ribosomes, a cell structure in which protein synthesis occurs in the cell cytoplasm. // The RNA molecules that are structural components of ribosomes.

Answer 127

Organelle composed of protein and rRNA that is the site of protein synthesis. // Particle composed of rRNAs and ribosomal proteins that catalyzes the synthesis of protein using information provided by mRNA. // A cellular organelle that assembles new proteins from amino acids according to the instructions carried by messenger RNA. // A molecular machine composed of RNA and protein that is the site of protein synthesis. // Cytoplasmic organelle on which proteins are synthesized. // The site of protein synthesis in a cell, composed of RNA and protein.

Answer 128

An enzyme consisting of RNA that specifically acts on strands of RNA to remove introns and splice together the remaining exons. // An RNA molecule with catalytic activity. // An RNA molecule with catalytic activity. // Catalytic RNA. // Ribonucleic acid molecules with catalytic activities; RNA enzymes.

Answer 129

Posttranscriptional modification of an mRNA that alters the meaning of one or more codons during translation. // Enzymatic modification of a base in messenger RNA. // Posttranscriptional processes that alter the information encoded in gene transcripts (RNAs). // The introduction into an RNA molecule of nucleotides that are not specified by a cellular or viral gene. // Type of RNA processing that alters the nucleotide sequence of an RNA transcript after it is synthesized by inserting, deleting, or altering individual nucleotides.

Answer 130

A mechanism of posttranscriptional regulation of gene expression by small RNA molecules that induce mRNA degradation or inhibition of translation. // Selective destruction of a messenger // A class of RNA molecules that silence gene expression. // A phenomenon in which double-stranded RNA prevents the expression of a gene homologous to at least part of the RNA. // As originally described, mechanism by which an experimentally introduced double-stranded RNA induces sequence-specific destruction of complementary mRNAs. The term RNAi is often used to include the inhibition of gene expression by microRNAs (miRNAs) and piwi RNAs (piRNAs), which are encoded in the cell’s own genome.

Answer 131

Functional unit of skeletal muscle. // A functional and structural unit of the muscle contractile system. // A functional compartment of the muscle fiber. // The contractile element between Z lines in a myofibril; contains the thick and thin fi laments that slide along one another to cause muscle contraction. // The contractile unit of a muscle, composed of myosin and actin, among other proteins. sarcoplasmic reticulum Tubules and vesicles in a cell that regulate calcium levels.

Answer 132

Intracellular chemical modifying activity within a cell after a first messenger (hormone or neurotransmitter) binds to the plasma membrane. // A short-lived chemical signal in the cytosol that can trigger a biochemical response. Second messenger formation is usually stimulated by a first messenger (a neurotransmitter or hormone) acting at a G-protein-coupled cell surface receptor. Examples of second messengers are cyclic adenosine monophosphate (cAMP), cyclic guanosine monophosphate (cGMP), and inositol-1,4,5-triphosphate (IP3). // An effector molecule synthesized in a cell in response to an external signal (first messenger) such as a hormone. // Small intracellular signaling molecule that is formed or released for action in response to an extracellular signal and helps to relay the signal within the cell. Examples include cyclic AMP, cyclic GMP, IP3, Ca2+, and diacylglycerol. // Small molecules or ions (such as Ca2+) that are produced in response to a signal; they act to amplify the signal and carry it to the next stage within the cell. Second messengers generally act by binding to and modifying the activities of enzymes. // Small, diffusible molecules that mediate many effects of hormones.

Answer 133

The regular periodic or repeating patterns in the arrangement of protein chains. // Regular local folding pattern of a polymeric molecule; in proteins, α helices and β sheets. // The level of protein substructure that involves organization of chain sections into ordered arrangements such as β-pleated sheets or a helices. // The local spatial arrangement of the main-chain atoms in a segment of a polypeptide chain; also applied to polynucleotide structure. // The repetitive folding pattern of a polypeptide.

Answer 134

Production of two daughter DNA molecules, each containing one strand of the parental template and a newly synthesized complementary strand. // Replication of DNA by a mechanism in which the parental strands are conserved (remain intact) and serve as templates for the synthesis of new complementary strands. // The mechanism of DNA replication that leads to a daughter molecule with one old strand and one new strand. // The process by which DNA molecules are made containing one strand of old DNA and one strand of new DNA. // The process of DNA replication in which each double-stranded DNA molecule contains one original strand and one new strand.

Answer 135

A genomic base-pair change that helps distinguish one species from another or one subset of individuals in a population. // A single base pair in the DNA that varies in a population. // A variation between individuals in a population due to a relatively common difference in a specific nucleotide at a defined point in the DNA sequence. // The most common type of polymorphism in the human genome. // Positions in the genome that differ by a single base between individuals.

Answer 136

Small interfering RNA; An intermediate in the RNAi process in which the long double-stranded RNA has been cut up into short (~21 nucleotides) double-stranded RNA. // (Small interfering RNAs) - mRNAs produced without splicing, because their precursors lack introns and splice sites. // Small RNA molecules that base-pair with mRNAs to induce mRNA cleavage or inhibition of translation. Abbreviated siRNAs. // Small double-stranded RNAs that inhibit translation and/or cause degradation of the messenger RNA. // Synthetic molecules that are similar to miRNA and are used in biological experiments to silence genes. // Short (21–26 nucleotide) double-stranded RNAs that inhibit gene expression by directing destruction of complementary mRNAs. Production of siRNAs is usually triggered by exogenously introduced double-stranded RNA.

Answer 137

A complex of RNAs and proteins involved in the splicing of mRNAs in eukaryotic cells. // Large assembly of RNA and protein molecules that performs pre-mRNA splicing in eukaryotic cells. // The large complex that assembles on an introncontaining pre-mRNA before splicing; in mammalian cells, it comprises the small nuclear ribonucleoproteins containing U1, U2, U4, U5, and U6 small nuclear RNAs and 150 proteins. // The RNA/protein complex that excises introns from primary transcripts of nuclear genes in eukaryotes. // Nuclear ribonucleoproteins that remove introns from primary transcripts.

Answer 138

A cell with the ability to proliferate extensively and whose offspring can differentiate into specialized cell types. // Undifferentiated cell that can continue dividing indefinitely, throwing off daughter cells that can either commit to differentiation or remain a stem cell (in the process of selfrenewal). // An undifferentiated cell that gives rise to a variety of specialized cells. // The common, self-regenerating cells in bone marrow that give rise to differentiated blood cells such as erythrocytes and lymphocytes. // Unspecialized, immature cells.

Answer 139

A specific group of lipids, including cholesterol and hormones. // Group of lipids including bile salts, cholesterol, and some hormones; molecule is composed of four attached hydrocarbon rings. // A lipid composed of four fused hydrocarbon rings. // Lipids containing a cyclopentanoperhydrophenanthrene ring system. // Lipids whose structure is based on a tetracyclic carbon skeleton with three 6-membered and one 5-membered ring. Steroids occur in both plants and animals and have a variety of important hormonal functions.

Answer 140

Molecule on which an enzyme acts. superresolution Describes several approaches in light microscopy that bypass the limit imposed by the diffraction of light and successfully allow objects as small as 20 nm to be imaged and clearly resolved. // Substance binding to the active site of an enzyme; reactant in a chemical reaction. // Any compound with which an enzyme reacts. // The reactant molecule of a biochemical reaction that binds to an enzyme at the active site. // The starting material for an enzymatic reaction.

Answer 141

An antigen-binding protein that is located on the surfaces of killer T cells and mediates the cellular immune response of mammals. The genes that encode T-cell antigens are assembled from gene segments by somatic recombination processes that occur during T lymphocyte differentiation. // The antigen-binding receptor on the surface of T lymphocytes. // Transmembrane receptor for antigen on the surface of T lymphocytes, consisting of an immunoglobulin-like heterodimer. // The cell-surface receptor for antigen on T lymphocytes. It consists of a disulfide-linked heterodimer of the highly variable α and β chains in a complex with the invariant CD3 and ζ proteins, which have a signaling function. T cells carrying this type of receptor are often called α:β T cells. An alternative receptor made up of variable γ and δ chains is expressed with CD3 and ζ on a subset of T cells. // Molecules on T cells that recognize antigens.

Answer 142

One of the two types of antigen-specific lymphocytes responsible for adaptive immune responses, the other being the B cells. T cells are responsible for the cell-mediated adaptive immune reactions. They originate in the bone marrow but undergo most of their development in the thymus. The highly variable antigen receptor on T cells is called the T-cell receptor and recognizes a complex of peptide antigen bound to MHC molecules on cell surfaces. There are two main lineages of T cells: those carrying α:β receptors and those carrying γ:δ receptors. Effector T cells perform a variety of functions in an immune response, acting always by interacting with another cell in an antigen-specific manner. Some T cells activate macrophages, some help B cells produce antibody, and some kill cells infected with viruses and other intracellular pathogens. // One of a class of blood cells (lymphocytes) of thymic origin, involved in cell-mediated immune reactions. // Lymphocytes possessing no surface antibody but an antigen-recognizing T-cell receptor. // Cells that differentiate in the thymus gland and are primarily responsible for the T-cell-mediated or cellular immune response. // A type of lymphocyte, which develops from a stem cell processed in the thymus gland, that is responsible for cellmediated immunity. See also CTL (cytotoxic T lymphocyte), T helper cells, T regulatory cells. // Adaptive immune system cell that functions in cell-mediated immunity.

Answer 143

End of a chromosome, associated with a characteristic DNA sequence that is replicated in a special way. Counteracts the tendency of the chromosome otherwise to shorten with each round of replication. From Greek telos, end. // Noncoding regions of DNA at the ends of eukaryotic chromosomes. // Specialized nucleic acid structure found at the ends of linear eukaryotic chromosomes. // The unique structure found at the end of eukaryotic chromosomes. // A region of repeated sequences at the ends of linear, cellular chromosomes that is maintained (copied) by a specialized enzyme and that protects against loss of genetic information. // The end piece of the eukaryotic chromosome.

Answer 144

Complex three-dimensional form of a folded polymer chain, especially a protein or RNA molecule. // The large-scale bends and folds produced by interactions between the R groups of amino acids that are separated by large distances in the linear sequence of a protein chain. // The level of protein structure that involves the manner in which the entire protein chain is folded into a speciic three-dimensional arrangement. // The overall folding of a polypeptide. // The three-dimensional conformation of a polymer in its native folded state.

Answer 145

Copying information from DNA to form an RNA molecule. // Copying of DNA carrying genetic information into a complementary RNA. // Process of copying the base sequence of a gene into mRNA. // Process through which RNA is formed along a DNA template. The enzyme RNA polymerase catalyzes the formation of RNA from ribonucleoside triphosphates. // Synthesis of RNA on a DNA template. // The enzymatic process whereby the genetic information contained in one strand of DNA is used to specify a complementary sequence of bases in an mRNA chain. // The process by which messenger RNA directs the cell to assemble amino acids in a particular order as specified by the DNA code. // The process by which the genetic information encoded in DNA is read and used to synthesize RNA in the nucleus of the cell. A small portion of doublestranded DNA uncoils, and complementary ribonucleotides line up in the correct sequence for RNA synthesis. // The process of synthesizing a messenger RNA molecule according to genetic instructions encoded in DNA. // The process of synthesizing RNA from a DNA template. // Copying of one strand of DNA into a complementary RNA sequence by the enzyme RNA polymerase.

Answer 146

A protein that binds to the promoter of DNA or a gene that controls the transcription of the gene or the synthesis of mRNA from the DNA. // A protein that is able to bind to specific DNA sequences (called cis-elements) and thereby controls the expression of genes. // A protein that regulates the binding of RNA polymerase to a gene promoter. // A protein that regulates the transcription of genes. // In eukaryotes, a protein that affects the regulation and transcription initiation of a gene by binding to a regulatory sequence near or within the gene and interacting with RNA polymerase and/or other transcription factors. // DNA-binding proteins that are required for transcription or that increase the rate of transcription.

Answer 147

(1) Generally, the conversion of energy or information from one form to another. (2) The transfer of genetic information from one cell to another by means of a viral vector. // The transfer of DNA from one cell to another by a bacteriophage. See also generalized transduction; specialized transduction. // The cell-to-cell transfer of DNA by a bacteriophage. // The transformation of sensory stimulus energy into a cellular signal, such as a receptor potential. // Genetic recombination in bacteria mediated by bacteriophage. Abortive t: Bacterial DNA is injected by a phage into a bacterium, but it does not replicate. Generalized t: Any bacterial gene may be transferred by a phage to a recipient bacterium. Restricted t: Transfer of bacterial DNA by a temperate phage is restricted to only one site on the bacterial chromosome.

Answer 148

Adapter molecules that align each amino acid with its corresponding codon on the mRNA. Abbreviated tRNAs. // A kind of RNA that transports amino acids to the ribosomes, where they are joined together to make proteins. // A class of RNA molecules (Mr 25,000 to 30,000), each of which combines covalently with a specific amino acid as the first step in protein synthesis. // Set of small RNA molecules used in protein synthesis as an interface (adaptor) between mRNA and amino acids. Each type of tRNA molecule is covalently linked to a particular amino acid. // The type of RNA molecule that brings amino acids to the ribosomal site where they are incorporated into proteins.

Answer 149

The process in which the genetic information present in an mRNA molecule specifies the sequence of amino acids during protein synthesis. // Protein (polypeptide) synthesis directed by a specific messenger RNA; occurs on ribosomes. // Process involving RNA and ribosomes to produce a new protein. // Process of copying the base sequence of mRNA into the amino acid sequence of proteins in the ribosome. // Ribosomal protein synthesis. // The process by which the genetic information transcribed from DNA onto mRNA is read by tRNA and used to direct protein synthesis. //The process of synthesizing a protein molecule according to genetic instructions carried by a messenger RNA molecule. // The synthesis of protein by the reading of the messenger RNA code for the correct amino acids. // The use of mRNA as a template in the synthesis of protein. // Process by which the sequence of nucleotides in an mRNA molecule directs the incorporation of amino acids into protein. Occurs on a ribosome.

Answer 150

A membrane protein that catalyzes the transport of a molecule from one side of a biomembrane to the other side. // A membrane protein that transports neurotransmitters, or their precursors, across membranes to concentrate them in either presynaptic cytosol or synaptic vesicles. // Membrane transport protein that binds to a solute and transports it across the membrane by undergoing a series of conformational changes. Transporters can transport ions or molecules passively down an electrochemical gradient or can link the conformational changes to a source of metabolic energy such as ATP hydrolysis to drive active transport. Compare channel protein. See also membrane transport protein. // A carrier protein in the plasma membrane. // Proteins that span a membrane and transport specific nutrients, metabolites, ions, or proteins across the membrane; sometimes called permeases.

Answer 151

A DNA element that can move from one location in the genome to another. // Segment of DNA that can move from one genome position to another by transposition. // A mobile element in prokaryotes that contains a gene for transposase and other genes. // A small piece of DNA that can move from one DNA molecule to another. // A segment of DNA that can move from one position in the genome to another. // DNA elements that can move (“transpose”) from one position in a DNA molecule to another.

Answer 152

One of a class of genes that encode proteins that normally regulate the cell cycle by suppressing cell division. Mutation of one copy of the gene is usually without effect, but when both copies are defective, the cell is allowed to continue dividing without limitation, producing a tumor. // A cellular gene encoding a protein that negatively regulates cell proliferation; mutational inactivation of both copies of the genes is associated with tumor development. (Chapter 9) // A gene whose product is involved in the repression of cell division. // A growth-inhibiting gene in normal cells whose inactivation contributes to neoplasia. // Gene that appears to help prevent formation of a cancer. Loss-of-function mutations in such genes favor the development of cancer.

Answer 153

A small protein that can be attached to other proteins and functions as a protein interaction module or to target them for degradation by the proteasome. // A small protein that is attached to target proteins by specific E3 ubiquitin ligases; ubiquitylation is a posttranslational protein modification that helps to regulate the physiological activity of modified proteins by marking them for degradation or relocalization in the cell. // A ubiquitous protein that marks worn-out cellular proteins for destruction by the proteasome. // Small, highly conserved protein present in all eukaryotic cells that becomes covalently attached to lysines of other proteins. Attachment of a short chain of ubiquitins to such a lysine can tag a protein for intracellular proteolytic destruction by a proteasome. // A small, highly conserved eukaryotic protein that targets an intracellular protein for degradation by proteasomes. Several ubiquitin molecules are covalently attached in tandem to a Lys residue in the target protein by a specific ubiquitinating enzyme.

Answer 154

A complete, fully developed viral particle. // A viral particle. // An infectious virus particle.

Answer 155

A self-replicating, infectious, nucleic acid–protein complex that requires an intact host cell for its replication; its genome is either DNA or RNA. // Infectious complex of macromolecules that contain their genetic information either as DNA or RNA; viruses need host cells for replication and the formation of new viral particles. // A submicroscopic, parasitic, filterable agent consisting of a nucleic acid surrounded by a protein coat. // Particle consisting of nucleic acid (RNA or DNA) enclosed in a protein coat and capable of replicating within a host cell and spreading from cell to cell. // Pathogen composed of a nucleic acid genome enclosed in a protein coat. Viruses can replicate only in a living cell, because they do not possess the metabolic machinery for independent life. // Submicroscopic, obligate parasitic pathogens comprising genetic material (DNA or RNA) surrounded by a protective protein coat. (Chapter 1)

Answer 156

The analysis of x-ray diffraction patterns of a crystalline compound, used to determine the molecule’s threedimensional structure. // Technique for determining the threedimensional arrangement of atoms in a molecule based on the diffraction pattern of x-rays passing through a crystal of the molecule. // The process of using X-ray diffraction to determine the structure of a crystal. // A technique that uses X rays to determine the structure of molecules. // Method used for the determination of the three-dimensional protein structure by analyzing a protein crystal with an X-ray beam and recording the diffraction pattern of the X-ray reflection.

Answer 157

A compact secondary structure in proteins that is stabilized by intrachain hydrogen bonds between peptide bonds. // A pattern in the secondary structure of a protein that occurs when the amino acid chain is wrapped tightly in a coil, with the side chains extending outward. // The coiled secondary structure of a protein. // A helical conformation of a polypeptide chain, usually right-handed, with maximal intrachain hydrogen bonding; one of the most common secondary structures in proteins. // Common folding pattern in proteins, in which a linear sequence of amino acids folds into a righthanded helix stabilized by internal hydrogen-bonding between backbone atoms.

Answer 158

Rapid and specific change in the electric properties of a plasma membrane in response to a stimulus.

Answer 159

Energy-requiring movement of a substance across a membrane, via a transport protein, against a gradient (e.g., concentration, electric).

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