BIO - TERMS - FREQUENCY > 2 PT 1 Flashcards
(172 cards)
1
Q
action potential
A
A brief fluctuation in membrane potential caused by the rapid opening and closing of voltage-gated ion channels; also known as spike, nerve impulse, or discharge. Action potentials sweep like a wave along axons to transfer information from one place to another in the nervous system. // Rapid, transient, self-propagating electrical excitation in the plasma membrane of a cell such as a neuron or muscle cell. Action potentials, or nerve impulses, make possible long-distance signaling in the nervous system. // Self-propagating change in membrane potential occurring in excitable cells (e.g., neurons, muscle cells).
2
Q
acute-phase proteins // acute-phase reactants
A
Proteins with innate immune function whose production is increased in the presence of an infection (the acute-phase response). They circulate in the blood and participate in early phases of host defense against infection. An example is mannose-binding lectin. // Serum proteins whose concentration changes by at least 25% during inflammation. // Plasma proteins whose levels are elevated or reduced within 1 to 2 days of an acute stress.
3
Q
adaptor protein // adaptor
A
General term for a protein that functions solely to link two or more different proteins together in an intracellular signaling pathway or protein complex. // Signaling proteins, generally without their own enzymatic activities, that have binding sites for two or more cellular components and serve to bring those components together. // Nonenzymatic proteins that form physical links between members of a signaling pathway, particularly between a receptor and other signaling proteins. They recruit members of the signaling pathway into functional protein complexes.
4
Q
adjuvant
A
A substance added to a vaccine to increase its effectiveness. // A compound or mixture that stimulates immune responses to an antigen (Chapter 8) // Any substance that enhances the immune response to an antigen with which it is mixed.
5
Q
aerobic respiration // aerobic cellular respiration
A
Breakdown of nutrients (e.g., pyruvate, fatty acids) to produce ATP, water, and carbon dioxide. The process requires oxygen. // Process by which a cell obtains energy from sugars or other organic molecules by allowing their carbon and hydrogen atoms to combine with the oxygen in air to produce CO2 and H2O, respectively. // Respiration in which the final electron acceptor in the electron transport chain is molecular oxygen (O2).
6
Q
albumin
A
A plasma protein that accounts for approximately 60% of the total plasma protein. // (al-bū′min) Plasma protein important in regulating fluid balance. // A blood protein that is water soluble and carries a variety of salt and nutrients; it helps to maintain osmotic pressure of the blood.
7
Q
alkaloid
A
Organic bases found in plants; they are often poisonous. // A chemical substance containing nitrogen as part of a heterocyclic ring structure; often highly toxic or mind-altering. Alkaloids represent a diverse array of amino-acid-derived, often highly complex structures with potential effects on mammalian organisms. Used in medicine and pharmacy. // Naturally occurring organic bases, such as morphine.
8
Q
allergen
A
An antigen that evokes a hypersensitivity response. // (al′er-gen) Noninfectious substance that elicits an excessive response by the immune system (allergic reaction). // Any antigen that elicits an allergic reaction.
9
Q
anaerobe
A
An organism that lives without oxygen. Obligate anaerobes die when exposed to oxygen. // An organism that does not require molecular oxygen (O2) for growth. // Organisms that do not use oxygen as terminal electron acceptor.
10
Q
angiotensin II
A
(an′jē-ō-ten′sin) A peptide hormone, derived from angiotensin I, that increases blood pressure. // A product of angiotensin I that is produced in the lung by angiotensin-converting enzyme. Production of angiotensin II results in the release of aldosterone from the adrenal cortex and antidiuretic hormone from the pituitary gland. // The active form of the vasoconstrictor angiotensin.
11
Q
antibiotic
A
An antimicrobial agent, usually produced naturally by a bacterium or fungus. // One of many different organic compounds that are formed and secreted by various species of microorganisms and plants, are toxic to other species, and presumably have a defensive function. // A substance that kills or inhibits the growth of microorganisms.
12
Q
antigen-presenting cell (APC)
A
A macrophage, dendritic cell, or B cell that engulfs an antigen and presents fragments to T cells. // Immune cell that presents (displays) an antigen to T-lymphocytes; e.g., a macrophage. // Highly specialized cells that can process antigens and display their peptide fragments on the cell surface together with other, co-stimulatory, proteins required for activating naive T cells. The main antigen-presenting cells for naive T cells are dendritic cells, macrophages, and B cells.
13
Q
apoptosome
A
A large, multimeric protein structure that forms in the process of apoptosis when cytochrome c is released from mitochondria and binds Apaf-1. A heptamer of cytochrome c-Apaf-1 heterodimers assembles into wheel-like structure that binds and activates procaspase-9, an initiator caspase, to initiate the caspase cascade. // Heptamer of Apaf1 proteins that forms on activation of the intrinsic apoptotic pathway; it recruits and activates initiator caspases that subsequently activate downstream executioner caspases to induce apoptosis. // A cytoplasmic protein complex that activates caspases, causing apoptosis.
14
Q
atom
A
A submicroscopic particle that constitutes the fundamental building block of ordinary matter; the smallest identifiable unit of an element. // The smallest particle that displays properties of an element; composed of electrons, protons, and neutrons (except in hydrogen). // The smallest unit of matter that can enter into a chemical reaction.
15
Q
base excision repair
A
DNA repair pathway in which single faulty bases are removed from the DNA helix and replaced. Compare nucleotide excision repair. // Removal of an abnormal base by a DNA glycosylase. // The removal of abnormal or chemically modified bases from DNA.
16
Q
basement membrane
A
Thin mat of extracellular matrix that separates epithelial sheets, and many other types of cells such as muscle or fat cells, from connective tissue. Also called basal lamina. // An extracellular matrix structure beneath single-layered epithelia. // Selective molecular layer that attaches epithelial tissue to underlying connective tissue.
17
Q
bioinformatics
A
The computerized analysis of biological data, using methods derived from statistics, linguistics, mathematics, chemistry, biochemistry, and physics. The data are often nucleic acid or protein sequence or structural data, but can also involve experimental data from many sources, patient statistics, and materials in the scientific literature. Bioinformatics research focuses on methods for data storage, retrieval, and analysis. // The science of determining the function of genes through computer-assisted analysis. // The study of genetic and other biological information using computer and statistical techniques.
18
Q
Bond dissociation energy, D // bond energy
A
The amount of energy needed to break a bond and produce two radical fragments. // The energy required to break a bond. // The energy required to break 1 mol of the bond in the gas phase.
19
Q
calmodulin
A
Ubiquitous intracellular Ca2+-binding protein that undergoes a large conformation change when it binds Ca2+, allowing it to regulate the activity of many target proteins. In its activated (Ca2+-bound) form, it is called Ca2+/calmodulin. // Calcium-binding protein that is activated by binding Ca2+; it is then able to bind to and regulate the activity of a wide variety of enzymes. // A calcium-dependent enzyme activator.
20
Q
carbonic anhydrase
A
An enzyme that establishes equilibrium among carbon dioxide, water, and carbonic acid. // Enzyme that reversibly catalyzes the formation of carbonic acid (H2CO3) from CO2 and H2O. cardiac output Product of stroke volume multiplied by heart rate in a minute (e.g., 5 L/min). // The enzyme that converts carbon dioxide and water to carbonic acid.
21
Q
carcinoma
A
A cancer derived from epithelial tissue. // Cancer of epithelial cells. The most common form of human cancer. // Cancer of epithelial tissues.
22
Q
catabolite repression
A
Inhibition of the metabolism of alternative carbon sources by glucose. // Glucose-mediated reduction in the rates of transcription of operons that specify enzymes involved in catabolic pathways (such as the lac operon). // Repression of catabolic operons in the presence of glucose.
23
Q
cell cycle (cell-division cycle)
A
Th e orderly and reproducible sequence in which cells increase in size, duplicate the genome, segregate duplicated chromosomes, and divide. (Chapter 6) // The cyclical events that occur during the divisions of mitotic cells. The cell cycle oscillates between mitosis and the interphase, which is divided into G1, S, and G2. // Reproductive cycle of a cell: the orderly sequence of events by which a cell duplicates its chromosomes and, usually, the other cell contents, and divides into two.
24
Q
cellulose
A
Long, unbranched chains of glucose; major constituent of plant cell walls. // A polysaccharide that consists of glucose units bonded together by b-glycosidic linkages; the main structural component of plants, and the most abundant organic substance on Earth. // Fiber component and main structural polysaccharide in plant cell walls that is composed of repeating glucose units with a b1–4 linkage.
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cerebral cortex
(se-rē′bral kor′teks) Superficial layer of gray matter in the cerebrum. // Outermost layer of the hemispheres of the brain; the most complex structure in the human body. // The layer of gray matter that lies just under the surface of the cerebrum.
26
cholecalciferol (or vitamin D3)
The form of vitamin D that is made photochemically in the skin. // Formed in the skin when 7-dehydrocholesterol is exposed to UV light. // Accepted designation for cholecalciferol (a vitamin D-active substance derived from animal sterols)
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chromatography
A process in which complex mixtures of molecules are separated by many repeated partitionings between a flowing (mobile) phase and a stationary phase. // A method for separating and identifying the components from mixtures of molecules having similar chemical and physical properties. // A technique for separating a mixture of compounds into pure components. Different compounds adsorb to a stationary support phase and are then carried along it at different rates by a mobile phase.
28
circadian clock // circadian rhythm
Internal cyclical process that produces a particular change in a cell or organism with a period of around 24 hours, for example the sleep-wakefulness cycle in humans. // Any rhythm with a period of about 1 day. // Th e cycle (roughly 24 hours in humans) that regulates many physiological processes, such as sleep-wake cycles. (Chapter 1)
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clonal selection
From a population of T and B lymphocytes with a vast repertoire of randomly generated antigen-specific receptors, a given foreign antigen activates (selects) only those lymphocyte clones that display a receptor that fits the antigen. Explains how the adaptive immune system can respond to millions of different antigens in a highly specific way. // Selective growth stimulation by an antigen of a B-cell clone carrying a matching surface antibody. // The development of clones of B and T cells against a specific antigen.
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Coding strand (sense strand)
In DNA transcription, the DNA strand identical in base sequence to the RNA transcribed from it, with U in the RNA in place of T in the DNA; as distinct from the template strand. Also called the nontemplate strand. // The sense strand of double-helical DNA that contains the gene. // The strand of a gene whose base sequence corresponds to the base sequence of the RNA transcript.
31
commensalism
A symbiotic relationship in which two organisms live in association and one is benefited while the other is neither benefited nor harmed. // Ecological relationship between microbes and their host in which the microbe benefits but offers no benefit and causes no harm. // Relationship between two species in which one organism benefits and the other species is unaffected.
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complement system
A set of blood plasma proteins that act in a concerted fashion to destroy extracellular pathogens and infected cells; originally defi ned as a heat-labile activity that lysed bacteria in the presence of antibody (it “complemented” antibody action); the activated complement pathway also stimulates phagocytosis, chemotaxis, and infl ammation. (Chapter 4) // A set of plasma proteins that act together as a defense against pathogens in extracellular spaces. The pathogen becomes coated with complement proteins that facilitate its removal by phagocytes and that can also kill certain pathogens directly. Activation of the complement system can be initiated in several different ways. See classical pathway, alternative pathway, lectin pathway. // System of blood proteins that can be activated by antibody–antigen complexes or pathogens to help eliminate the pathogens, by directly causing their lysis, by promoting their phagocytosis, or activating an inflammatory response.
33
condensation reaction
A chemical reaction in which a molecule of water is released; also called dehydration synthesis. // A reaction in which two or more organic compounds are joined, often with the loss of water or some other small molecule. // Bond formation with release of a water molecule.
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confocal microscope // confocal microscopy
Type of light microscope that produces a clear image of a given plane within a solid object. It uses a laser beam as a pinpoint source of illumination and scans across the plane to produce a two-dimensional “optical section.” // A light microscope that uses fluorescent stains and laser to make two- and three-dimensional images. // Optical imaging technique increasing optical resolution and contrast of a microscopic picture based on the elimination of out-of-focus light in specimens that are thicker than the focal plane or depth of focus generated by the objective.
35
conjugate acid-base pair // conjugate redox pair
A proton donor and its corresponding deprotonated species; for example, acetic acid (donor) and acetate (acceptor). // Two substances related to each other by the transfer of a proton. // An electron donor and its corresponding electron acceptor form; for example, Cu (donor) and Cu2 (acceptor), or NADH (donor) and NAD (acceptor).
36
cooperativity
The characteristic of an enzyme or other protein in which binding of the first molecule of a ligand changes the affinity for the second molecule. In positive cooperativity, the affinity for the second ligand molecule increases; in negative cooperativity, it decreases. // Interactions between multiple binding sites for the same ligand in an allosteric protein. // The property of long-term potentiation, reflecting the requirement that many inputs be active at the same time during a tetanus to induce LTP. See also long-term potentiation.
37
cortisol
A corticosteroid hormone released from the adrenal cortex that stimulates the catabolism of proteins, the sparing of glucose utilization, an increase in gluconeogenesis, and an increase in free fatty acid mobilization. // A steroid hormone released by the adrenal cortex; mobilizes energy reserves, suppresses the immune system, and has direct actions on some CNS neurons. // The most important glucocorticoid; a stress hormone.
38
crista (plural cristae)
A specialized invagination of the inner mitochondrial membrane. // Folding of the inner membrane of a mitochondrion. // Infoldings of the inner mitochondrial membrane.
39
Crossing over
A process in which chromosomes exchange material through the breakage and reunion of their DNA molecules. (See also Recombination.) // The process by which a portion of one chromosome is exchanged with a portion of another chromosome. // The exchange of DNA between homologous chromosomes during meiosis and (rarely) mitosis.
40
cyclin
One of a family of proteins that activate cyclin-dependent protein kinases and thereby regulate the cell cycle. // Protein that periodically rises and falls in concentration in step with the eukaryotic cell cycle. Cyclins activate crucial protein kinases (called cyclin-dependent protein kinases, or Cdks) and thereby help control progression from one stage of the cell cycle to the next. // Activators of cyclin-dependent protein kinases.
41
cytopathic effect (CPE)
Deleterious morphological changes induced in cells by viral infection. (Chapter 3) // A visible effect on a host cell, caused by a virus, that may result in host cell damage or death. // The morphological changes induced in cells by viral infection. (Chapter 2)
42
dalton (da)
The mass of a hydrogen atom. // Unit of atomic or molecular weight; 1 dalton (Da) is the weight of a hydrogen atom (1.66 x 10⁻²⁴ g). // The measure of molecular mass; equals 1g/mole.
43
dendritic cell (DC)
Phagocytic cells of the skin and mucous membranes. // A type of antigen-presenting cell characterized by long fingerlike extensions; found in lymphatic tissue and skin. // Bone marrow-derived cells found in most tissues, including lymphoid tissues. There are two main functional subsets. Conventional dendritic cells take up antigen in peripheral tissues, are activated by contact with pathogens, and travel to the peripheral lymphoid organs, where they are the most potent stimulators of T-cell responses. Plasmacytoid dendritic cells can also take up and present antigen, but their main function in an infection is to produce large amounts of the antiviral interferons as a result of pathogen recognition through receptors such as TLRs. Both these types of dendritic cells are distinct from the follicular dendritic cell that presents antigen to B cells in lymphoid follicles.
44
desmosome
(dez′mō-sōm) One type of adhesion between two epithelial cells; a type of intercellular junction that holds cells together at a single point (like a button). // Anchoring cell–cell junction, usually formed between two epithelial cells. Characterized by dense plaques of protein into which intermediate filaments in the two adjoining cells insert. // Spot welds that hold neighboring cells together.
45
disulfide bond
A covalent bond involving the oxidative linkage of two Cys residues, from the same or different polypeptide chains, forming a cystine residue. // A covalent bond formed by an oxidative reaction between two sulfhydryl groups. // A covalent bond that holds together two atoms of sulfur. DNA base composition The moles-percentage of guanine plus cytosine in an organism’s DNA.
46
domain // protein domain
A distinct structural unit of a polypeptide; domains may have separate functions and may fold as independent, compact units. // A taxonomic classification based on rRNA sequences; above the kingdom level. // Portion of a protein that has a tertiary structure of its own. Larger proteins are generally composed of several domains, each connected to the next by short flexible regions of polypeptide chain. Homologous domains are recognized in many different proteins.
47
electrochemical gradient
Combined influence of a difference in the concentration of an ion on two sides of a membrane and the electrical charge difference across the membrane (membrane potential). Ions or charged molecules can move passively only down their electrochemical gradient. // Electrical charge difference across a membrane. // The resultant of the gradients of concentration and of electric charge of an ion across a membrane; the driving force for oxidative phosphorylation and photophosphorylation.
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Electronegativity (EN)
An atom’s ability to attract electrons to itself in a covalent bond. // The tendency of an atom to attract electrons. // The ability of an atom to attract electrons in a covalent bond. Electronegativity increases across the periodic table from left to right and from bottom to top.
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embryonic stem cell (ESC // ES cell)
A cell from an embryo that has the potential to become a wide variety of specialized cell types. // Cells derived from the inner cell mass of the early mammalian embryo. Capable of giving rise to all the cells in the body. Can be grown in culture, genetically modified, and inserted into a blastocyst to develop a transgenic animal. // Cells present in embryos that can differentiate into many different types of tissues and/or organs.
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endosome
Cell structures that transport a variety of compounds to either lysosomes for degradation or to the cell membrane surface for recycling. // An organelle derived from endocytic vesicles. // A vesicle that transports molecules from the plasma membrane to the cell interior. (Chapter 5)
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enthalpy (H)
The energy content of a molecule. // The sum of the internal energy of a system and the product of its pressure and volume. // The heat content of a system.
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epidermis
Epithelial layer covering the outer surface of the body. Has different structures in different animal groups. The outer layer of plant tissue is also called the epidermis. // (ep-i-derm′is) The epithelium (keratinized, stratified squamous) of the integument. // The outer portion of the skin.
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epinephrine
A catecholamine neurotransmitter synthesized from norepinephrine; also called adrenaline. // (ep′i-nef′rin) Hormone released by the adrenal medulla during activation of the sympathetic nervous system. // Synonym for adrenaline, a stress hormone from the adrenal medulla.
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essential amino acid
An amino acid needed for health and maintenance and that must be ingested because the tissues of the body cannot synthesize it. // One of nine amino acids that are biosynthesized only in plants and microorganisms and must be obtained by humans in the diet. // Amino acids that cannot be synthesized by humans (and other vertebrates) and must be obtained from the diet.
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extracellular matrix (ECM)
(mā′triks) Protein fibers and ground substance in the extracellular space of connective tissue. // The network of fibrous proteins deposited in the space between cells. // An interwoven combination of glycosaminoglycans, proteoglycans, and proteins, just outside the plasma membrane, that provides cell anchorage, positional recognition, and traction during cell migration.
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family // family (group)
A group of organic compounds with the same functional group. // A taxonomic group between order and genus. // Columns within the main-group elements in the periodic table that contain elements that exhibit similar chemical properties.
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ferritin
A large and complex molecule consisting of 24 polypeptides that functions to store 4,500 atoms of iron for each molecule. // One of several human iron-binding proteins that reduce iron available to a pathogen. // The principal intracellular iron storage protein; trace amounts are present in the plasma.
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fibrinogen
The inactive precursor protein of fibrin. // A protein produced by the liver that forms a fibrin clot following the action of prothrombin. // The circulating precursor of fibrin.
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fibrous protein
A protein with a relatively linear structure; fibrous proteins tend to be insoluble in aqueous solutions. // Insoluble proteins that serve a protective or structural role; contain polypeptide chains that generally share a common secondary structure. // A type of protein that consists of polypeptide chains arranged side by side in long threads. Such proteins are tough, insoluble in water, and used in nature for structural materials such as hair, hooves, and ingernails.
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fluid mosaic model
A model describing biological membranes as a fluid lipid bilayer with embedded proteins; the bilayer exhibits both structural and functional asymmetry. // A way of describing the dynamic arrangement of phospholipids and proteins comprising the plasma membrane. // A model of membrane structure that assumes globular proteins are embedded in a lipid bilayer.
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Fluorescence resonance energy transfer (also Förster resonance energy transfer both abbreviated with FRET)
Mechanism that describes the nonradiative energy transfer between two fluorophores; prerequisites for energy transfer from donor fluorophore to acceptor fluorophore are the small distance between both (Förster radius) and the spectral overlap of the donor emission spectrum and the acceptor absorption spectrum. // Technique for monitoring the closeness of two fluorescently labeled molecules (and thus their interaction) in cells. Also known as Förster resonance energy transfer. // A technique for estimating the distance between two proteins or two domains of a protein by measuring the nonradiative transfer of energy between reporter chromophores when one is excited and the fluorescence emitted from the other is quantified.
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fungus (plural fungi)
A kingdom of single-celled and multicellular eukaryotic organisms, including the yeasts and molds, that can cause a variety of diseases. Immunity to fungi is complex and involves both humoral and cell-mediated responses. // Kingdom of eukaryotic organisms that includes the yeasts, molds, and mushrooms. Many plant diseases and a relatively small number of animal diseases are caused by fungi. // An organism that belongs to the Kingdom Fungi; a eukaryotic absorptive chemoheterotroph.
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futile cycle
A biochemical reaction cycle that is wasting energy, e.g., a simultaneous action of a kinase generating a phosphorylated intermediate that is subsequently and immediately degraded by a phosphatase. // A cycle of enzyme-catalyzed reactions that results in release of thermal energy by the hydrolysis of ATP. // Simultaneous activity of two opposing metabolic reactions, leading to ATP hydrolysis.
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gap junction
Communicating channel-forming cell–cell junction present in most animal tissues that allows ions and small molecules to pass from the cytoplasm of one cell to the cytoplasm of the next. // A small aqueous channel connecting the cytoplasm of neighboring cells. // A specialized junction where a narrow gap between two cells is spanned by protein channels (connexons) that allow ions to pass directly from one cell to another.
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gene therapy
Treating a disease by replacing abnormal genes. // The introduction of a functional gene into the patient’s cells. // The treatment of inherited diseases by introducing wild-type copies of the defective gene causing the disorder into the cells of affected individuals. If reproductive cells are modified, the procedure is called germ-line or heritable gene therapy. If cells other than reproductive cells are modified, the procedure is called somatic-cell or noninheritable gene therapy.
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genomic library
A DNA library containing DNA segments that represent all (or most) of the sequences in an organism’s genome. // Collection of cloned DNA molecules representing an entire genome. // A collection of cloned DNA fragments created by inserting restriction enzyme fragments in a bacterium, yeast, or phage.
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globular protein
A protein that folds into a roughly spherical shape so that its polar side chains are oriented outward and its nonpolar side chains, toward the interior; globular proteins tend to be soluble in water. // A type of protein that is coiled into a compact, nearly spherical shape. Globular proteins, which are generally water-soluble and mobile within the cell, are the structural class to which enzymes belong. // Soluble proteins with a globular (somewhat rounded) shape.
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glucose
(glū′kōs) A monosaccharide; primary nutrient source for cellular respiration. // The most abundant monosaccharide in food carbohydrate and the primary carbohydrate that circulates in the blood. // The most common mechanism for transporting carbohydrates in the body; primarily broken down by the glycolytic energy system.
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Gram negative // gram-negative bacteria
Description for bacteria that do not stain with Gram stain as a result of having a thinner peptidoglycan cell wall outside their inner (plasma) membrane, and on an additional outer membrane. // Bacteria that lose the crystal violet color after decolorizing by alcohol; they stain red after treatment with safranin. // Bacteria that fail to retain crystal violet stain following alcohol wash due to a thin peptidoglycan layer.
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growth factor
Extracellular signal protein that can stimulate a cell to grow. They often have other functions as well, including stimulating cells to survive or proliferate. Examples include epidermal growth factor (EGF) and platelet-derived growth factor (PDGF). // Proteins or other molecules that act from outside a cell to stimulate cell growth and division. // Soluble extracellular proteins that stimulate the proliferation or differentiation of cultured cells.
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GTPase-activating protein (GAP)
Regulatory proteins that bind activated G proteins and stimulate their intrinsic GTPase activity, speeding their self-inactivation. // Protein that binds to a GTPase and inhibits it by stimulating its GTPase activity, causing the enzyme to hydrolyze its bound GTP to GDP. // Regulatory proteins that accelerate the intrinsic GTPase activity of G proteins and thus facilitate the conversion of G proteins from the active (GTP-bound) state to the inactive (GDP-bound) state.
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Haploid (monoploid)
(hap′loyd) The number of chromosomes in a sperm or secondary oocyte. In humans, the haploid number is 23. // Having a single set of genetic information; describes a cell with one chromosome of each type. Compare diploid. // An organism or cell having only one complete set (n) of chromosomes or one genome.
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heme // heme iron
The iron-porphyrin prosthetic group of heme proteins. // (hēm) Portion of a hemoglobin molecule that binds iron, which transports oxygen. // A form of iron. Heme is a large heterocyclic organic molecule that contains an iron atom at the center of a prosthetic ring structure, known as a porphyrin ring.
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heterogeneous nuclear RNA (hnRNA)
The original RNA synthesized in the nucleus as a copy of the DNA before any modification. // The population of primary transcripts in the nucleus of a eukaryotic cell. // Nuclear precursors to mRNAs that are larger than mRNAs and heterogeneous in size. (Chapter 10)
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hexose
A simple sugar with a backbone containing six carbon atoms.
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holoenzyme
A catalytically active enzyme, including all necessary subunits, prosthetic groups, and cofactors. // An enzyme consisting of an apoenzyme and a cofactor. // The form of a multimeric enzyme in which all of the component polypeptides are present.
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homeotic genes // homeotic selector gene
Genes that regulate development of the pattern of segments in the Drosophila body plan; similar genes are found in most vertebrates. // A group of genes whose products control formation of the body of an embryo by regulating the expression of other genes in segmental regions along the anterior–posterior axis. // In Drosophila development, a gene that defines and preserves the differences between body segments.
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homozygous
(hō-mō-zı̄′gŭs) Having two identical alleles for a trait. // Carrying two identical variants of a gene. // Describes individuals that have two identical alleles of a given gene, inherited separately from each parent.
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human immunodeficiency virus (HIV)
The causative agent of the acquired immune deficiency syndrome (AIDS). HIV is a retrovirus of the lentivirus family that selectively infects macrophages and CD4 T cells, leading to their slow depletion, which eventually results in immunodeficiency. There are two major strains of the virus, HIV-1 and HIV-2, of which HIV-1 causes most disease worldwide. HIV-2 is endemic to West Africa but is spreading. // The retrovirus that causes acquired immune deficiency syndrome (AIDS) in humans. // The retrovirus that causes AIDS in humans.
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Huntington’s disease (HD)
An inherited neurodegenerative disease caused by expansion of a trinucleotide repeat. // A hereditary, progressive, inevitably fatal condition characterized by dyskinesias, dementia, and personality disorders; associated with profound degeneration of neurons in the basal ganglia and cerebral cortex. // A late-onset (age 30 to 50 years) neurodegenerative disorder in humans caused by an autosomal dominant mutation. The genetic defect is an expanded (CAG)n trinucleotide repeat that encodes an abnormally long polyglutamine region near the amino terminus of the huntingtin gene product.
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hydroxyapatite
(hı̄-drok′sē-ap-ă- tı̄t) Natural mineral structure that the crystal lattice of bone and teeth closely resembles. // The calcium-containing crystalline unit of bone. // The major inorganic component of bone.
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IgA
Immunoglobulin A; the principal class of antibody in secretions, including saliva, tears, milk, and respiratory and intestinal secretions. // Immunoglobulin class composed of α heavy chains that can occur in a monomeric and a polymeric (mainly dimeric) form. Polymeric IgA is the main antibody secreted by mucosal lymphoid tissues. // The class of antibodies found in secretions.
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IgE
Immunoglobulin E; binds with high affinity via its tail region to a class of Fc receptors on the surface of mast cells (tissues) or basophils (blood), where it acts as an antigen receptor; antigen binding stimulates the secretion of cytokines and biologically active amines, which help attract white blood cells, antibodies, and complement proteins to the site of activation. // Immunoglobulin class composed of ε heavy chains that acts in defense against parasite infections and in allergic reactions. // The class of antibodies involved in hypersensitivities.
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IgM
Immunoglobulin class composed of μ heavy chains that is the first to appear on B cells and the first to be secreted. // Immunoglobulin M; the first class of immunoglobulin that a developing B cell in the bone marrow makes, forming B-cell receptors on its surface. IgM antibodies are the major class of antibody secreted into the blood in the early stages of a primary antibody response on first exposure to an antigen, where their pentameric structure (with 10 antigen-binding sites) allows strong binding to pathogens. When bound to antigen, it is highly efficient activation of complement. // The first class of antibodies to appear after exposure to an antigen.
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immunoglobulin (Ig) superfamily
Large and diverse family of proteins that contain immunoglobulin or immunoglobulin-like domains. Most are involved in cell–cell interactions or antigen recognition. // Large and diverse family of proteins that contain immunoglobulin domains or immunoglobulin-like domains. Most are involved in cell–cell interactions or antigen recognition. // Large family of proteins with at least one Ig or Ig-like domain, many of which are involved in antigen recognition and cell– cell interaction in the immune system and other biological systems. // The protein family to which antibodies and B-cell receptors belong.
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in vitro
“In glass”; that is, in the test tube. // In the laboratory or test tube. // From the Latin meaning “within glass”; biological processes made to occur experimentally outside the organism in a test tube or other container.
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initiation codon
AUG (sometimes GUG or, even more rarely, UUG in bacteria and archaea); codes for the first amino acid in a polypeptide sequence N-formylmethionine in bacteria; methionine in archaea and eukaryotes. // A sequence of three nucleotides in mRNA— usually AUG, sometimes GUG—that signals the initiation of a new polypeptide during translation. // The codon at which translation of an mRNA begins, most commonly AUG. (Chapter 11)
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interleukin (IL)
A chemical that causes T-cell proliferation. See also cytokine. // A generic name for cytokines produced by leukocytes. The more general term cytokine is used in this book, but the term interleukin is used in the naming of specific cytokines such as IL-2. Some key interleukins are listed in the glossary under their abbreviated names, for example IL-1β and IL-2. Cytokines are listed in Appendix III. // Secreted cytokines that allow communication among leukocytes. (Chapter 4)
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intrinsic factor
Accepted designation for the vitamin B12-binding protein produced by gastric parietal cells and necessary for the enteric absorption of the cobalamins // A glycoprotein from parietal cells in the stomach; required for efficient vitamin B12 absorption. // Chemical, produced by stomach cells, required for absorption of vitamin B12.
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ion
An atom or molecule with a net charge caused by the loss or gain of electrons. // A negatively or positively charged atom or group of atoms. // An atom or molecule that has a net electrical charge because of a difference in the number of electrons and protons.
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isoelectric pH (isoelectric point, pI)
The pH at which a solute has no net electric charge and thus does not move in an electric field. // The pH value at which the number of positive charges on the molecule equals the number of negative charges. // The pH at which the number of positive charges and the number of negative charges on a protein or an amino acid are equal.
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Janus kinase (JAK) // Janus kinase (JAK) family
A type of tyrosine kinase that associates with activated receptors for cytokines, growth hormone, prolactin, and erythropoietin. // Enzymes of the JAK–STAT intracellular signaling pathways that link many cytokine receptors with gene transcription in the nucleus. The kinases phosphorylate STAT proteins in the cytosol, which then move to the nucleus and activate a variety of genes. // Cytoplasmic tyrosine kinases associated with cytokine receptors, which phosphorylate and activate transcription regulators called STATs.
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kinetochore
Large protein complex that connects the centromere of a chromosome to microtubules of the mitotic spindle. // A proteinaceous structure associated with the centromere of a chromosome during eukaryotic cell division; the point at which microtubules attach to move the chromosome through the division process. // A proteinaceous structure on the centromere to which spindle fibers attach.
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latent infection
A condition in which a pathogen remains in the host for long periods without producing disease. // A class of persistent infection that lasts the life of the host; few or no virus particles can be detected, despite continuous presence of the viral genome. (Chapter 5) // Long term infection in which the viral genome is maintained with limited expression of viral genes and without loss of host cell viability. (Chapters 8 and 9)
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Ligase
A type of enzyme that forms a bond while hydrolyzing a high-energy phosphate. // An enzyme that joins the ends of two strands of nucleic acid. // Enzymes that catalyze condensation reactions in which two atoms are joined using the energy of ATP or another energy-rich compound.
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lipoate (lipoic acid)
A prosthetic group of pyruvate dehydrogenase. // Cofactor in oxidative decarboxylation of α-keto acids; essential for growth of several microbes but inconsistent effects on animal growth Pyrroloquinoline quinone Component of certain bacterial and mammalian metallooxidoreductases; deprivation impairs growth, causes skin lesions in mice // A vitamin for some microorganisms; an intermediate carrier of hydrogen atoms and acyl groups in -keto acid dehydrogenases.
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lysis
(1) Destruction of a cell by the rupture of the plasma membrane, resulting in a loss of cytoplasm. (2) In disease, a gradual period of decline. // Bursting of a cell by the destruction of the cell membrane following infection by a virus. // Destruction of a plasma membrane or (in bacteria) cell wall, releasing the cellular contents and killing the cell.
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M (microfold) cell
Cells that take up and transfer antigens to lymphocytes, on Peyer’s patches. // Microfold or membranous epithelial cell; cells of mucosal surfaces specialized for delivery of antigens to underlying lymphoid tissues. (Chapters 2 and 4) // Specialized epithelial cell type in the intestinal epithelium over Peyer’s patches, through which antigens and pathogens enter from the gut.
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mass number (A)
Total number of neutrons and protons in the nucleus of an atom. // The sum of the number of protons and neutrons in an atom. // The total of protons plus neutrons in an atom.
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mast cell
A type of cell found throughout the body that contains histamine and other substances that stimulate vasodilation. // A large granule-rich cell found in connective tissues throughout the body, most abundantly in the submucosal tissues and the dermis. The granules store bioactive molecules including the vasoactive amine histamine, which are released on mast-cell activation. Mast cells are thought to be involved in defenses against parasites and they have a crucial role in allergic reactions. // Resident cells that secrete heparin and histamine during inflammation; often found near blood vessels.
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melanin
(mel′ă-nin) Any of the dark brown-black pigments or yellow-red pigments that occur in the skin, hair, and retina. // The dark pigment of skin and hair. // Brown or black pigment.
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metabolic syndrome
A combination of medical conditions that together predispose to cardiovascular disease and type 2 diabetes. They include high blood pressure, high concentrations of LDL and triacylglycerol in the blood, slightly elevated fasting blood glucose concentration, and obesity. // A set of blood and anthropometric conditions that increase the risk of diseases, in particular, cardiovascular disease and Type 2 diabetes. // The abnormalities seen in people who eat more than they can metabolize.
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micelle
An aggregate of amphipathic molecules in water, with the nonpolar portions in the interior and the polar portions at the exterior surface, exposed to water. // Small globule or sheet formed from amphipathic lipids. // Spherical clusters of soaplike molecules that aggregate in aqueous solution. The ionic heads of the molecules lie on the outside, where they are solvated by water, and the organic tails bunch together on the inside of the micelle.
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microfilament
(mı̄-krō-fil′ă- ment) Smallest structural protein of the cytoskeleton; composed of actin. // A polymer of the protein actin, forming a braided strand 5 nm in diameter; a component of the cytoskeleton. // Cytoskeletal fibers formed by the polymerization of actin.
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microsome
Small vesicle derived from endoplasmic reticulum that is produced by fragmentation when cells are homogenized. // Fragments of the endoplasmic reticulum obtained by cell fractionation. // Membranous vesicles formed by fragmentation of the endoplasmic reticulum of eukaryotic cells; recovered by differential centrifugation.
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morbidity // morbidity rate
(1) The incidence of a specific disease. (2) The condition of being diseased. // Th e percentage of individuals in a specifi ed population who show symptoms of infection in a given period. (Chapter 1) // The number of people affected by a disease in a given period of time in relation to the total population.
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mTOR (mammalian target of rapamycin)
An enzyme involved in a metabolic signaling pathway found in muscle that supports protein synthesis and regulation of cell growth, cell proliferation, cell motility, and cell survival, among other functions. The term is an acronym for mammalian target of rapamycin. // The mammalian version of the large protein kinase called TOR, involved in cell signaling; mTOR exists in two functionally distinct multiprotein complexes. // Serine/threonine kinase that functions in regulating numerous aspects of cell metabolism and function in complex with regulatory proteins Raptor or Rictor. The Raptor/mTOR complex (mTORC1) is inhibited by the immunosuppressive drug rapamycin.
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muscle fiber
Skeletal muscle cell. // A multinucleated skeletal muscle cell. // An alternative term for a muscle cell based on the thin, elongated appearance of muscle cells; the unit responsible for contraction.
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mutarotation
The change in specific rotation of a pyranose or furanose sugar or glycoside accompanying the equilibration of its - and -anomeric forms. // Spontaneous interconversion of anomeric forms in a monosaccharide. // The change in optical rotation observed when a pure anomer of a sugar is dissolved in water. Mutarotation is caused by the reversible opening and closing of the acetal linkage, which yields an equilibrium mixture of anomers.
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natural selection
Process by which organisms with certain inherited characteristics are more likely to survive and reproduce than organisms with other characteristics. // The process of differential survival and reproduction that changes allele frequencies from generation to generation. // Differential survival and reproduction in nature that favors individuals that are better adapted to their environment; elimination of less fit organisms.
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neurofilament
(nūr-o-fil′a-ment) Group of intermediate-sized filaments in a neuron. // Type of intermediate filament found in nerve cells. // A type of intermediate fi lament found in neurons, 10 nm in diameter; an important component of the neuronal cytoskeleton.
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nuclear magnetic resonance (NMR) // nuclear magnetic resonance spectroscopy
A technique that utilizes certain quantum mechanical properties of atomic nuclei to study the structure and dynamics of the molecules of which they are a part. // NMR is the resonant absorption of electromagnetic radiation at a specific frequency by atomic nuclei in a magnetic field, due to flipping of the orientation of their magnetic dipole moments. The NMR spectrum provides information about the chemical environment of the nuclei. NMR is used widely to determine the three-dimensional structure of small proteins and other small molecules. The principles of NMR are also used for medical diagnostic purposes in magnetic resonance imaging (MRI). // A spectroscopic technique that provides information about the carbon–hydrogen framework of a molecule. NMR works by detecting the energy absorptions accompanying the transitions between nuclear spin states that occur when a molecule is placed in a strong magnetic ield and irradiated with radiofrequency waves.
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open reading frame (ORF)
A group of contiguous nonoverlapping nucleotide codons in a DNA or RNA molecule that does not include a termination codon. // A continuous nucleotide sequence free from stop codons in at least one of the three reading frames (and thus with the potential to code for protein). // A DNA segment containing the sequences required to encode a polypeptide. The RNA transcript of an ORF begins with a translation start codon, followed by a sequence of codons specifying amino acids, and ending with a translation stop codon. An ORF is presumed, but not known, to encode a polypeptide.
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origin // Origin of replication
The nucleotide sequence or site in DNA where DNA replication is initiated. // The site or nucleotide sequence on a chromosome or DNA molecule at which replication is initiated. // Specific sites at which replication of DNA begins. (Chapter 9)
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osteoblast
(os′tē-ō-blast) A dividing cell in bone, which produces bone matrix. // Cell that secretes matrix of bone. // Bone cell responsible for bone synthesis.
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palindrome
A segment of duplex DNA in which the base sequences of the two strands exhibit twofold rotational symmetry about an axis. // A segment of DNA in which the base-pair sequence reads the same in both directions from a central point of symmetry. // A type of symmetrical DNA sequence.
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pattern recognition receptor (PRR)
Protein receptors of the innate immune system that bind defi nitive molecular features of pathogens; present in sentinel cells, such as immature dendritic cells and macrophages. (Chapter 3) // Receptor present on or in cells of the innate immune system that recognizes and is activated by microbial pathogen-associated molecular patterns (PAMPs). // Receptors of the innate immune system that recognize common molecular patterns on pathogen surfaces.
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peptide
Two or more amino acids covalently joined by peptide bonds. // A compound containing amino acids; a breakdown or buildup unit in protein metabolism. // A type of short amino acid polymer in which the individual amino acid residues are linked by amide bonds.
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peripheral nervous system (PNS)
The nerves that connect the outlying parts of the body with the central nervous system. // The parts of the nervous system other than the brain and spinal cord. The PNS includes all the spinal ganglia and nerves, cranial nerves III–XII, and the autonomic nervous system. See also central nervous system. // Composed of nerves and ganglia that are outside of the central nervous system.
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phenylketonuria (PKU)
Metabolic disorder resulting in mental retardation; transmitted as a Mendelian recessive and treated in early childhood by special diet. // An inborn error of metabolism in which phenylalanine is unable to be metabolized to tyrosine due to a defect in the enzyme phenylalanine hydroxylase. If untreated, PKU can lead to mental retardation, epileptic seizures, and skin lesions. // Inherited deficiency of phenylalanine hydroxylase, causing mental retardation.
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phosphorylase (PHOS)
The enzyme responsible for stimulating muscle glycogen breakdown. // A type of enzyme that cleaves a bond by the addition of phosphate. // Enzymes that catalyze phosphorolysis.
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platelet
(plāt′let) Irregularly shaped cell fragment that participates in hemostasis. // Cell fragment, lacking a nucleus, that breaks off from a megakaryocyte in the bone marrow and is found in large numbers in the bloodstream. Helps initiate blood clotting when blood vessels are injured. // Small, enucleated cells that initiate blood clotting; they arise from bone marrow cells called megakaryocytes. Also known as thrombocytes.
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polyunsaturated fatty acids // polyunsaturated
A fatty acid in which there are two or more double bonds in the hydrocarbon side chain. // Fatty acids containing more than one C═C double bond. // Fatty acids that contain more than one double bond.
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posttranslational modification
Enzymatic processing of a polypeptide chain after translation from its mRNA. // A chemical modiication of a protein that occurs after translation from DNA. // Modifications of proteins by enzymatic reactions after translation of the mRNA to the amino acid sequence. The most frequent modifications are phosphorylation, glycolysation, and acetylation.
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primer
A short oligomer (of sugars or nucleotides, for example) to which an enzyme adds additional monomeric subunits. // A free 3’-OH group required for initiation of synthesis of DNA from DNA or RNA templates and initiation of synthesis of some viral RNA genomes. (Chapters 6 and 9) // A short nucleotide sequence with a reactive 3′ OH that can initiate DNA synthesis along a template.
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processivity
For any enzyme that catalyzes the synthesis of a biological polymer, the property of adding multiple subunits to the polymer without dissociating from the substrate. // The ability of a DNA or RNA polymerase to synthesize long strands without interruption. // The ability of an enzyme to copy a nucleic acid template over long distances from a single site of initiation. ( Chapters 7, 8, and 9)
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protease
An enzyme that digests protein (proteolytic enzymes). // Any enzyme that hydrolyzes proteins. // Enzymes that catalyze the hydrolytic cleavage of peptide bonds in proteins.
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provirus
A viral chromosome that has integrated into a host—either prokaryotic or eukaryotic—genome (cf. Prophage). // The DNA form of a retrovirus when it is integrated into the hostcell genome, where it can remain transcriptionally inactive for long periods. // Viral DNA that is integrated into the host cell’s DNA.
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pus
(pŭs) Substance composed of dead pathogens, white blood cells, and cellular debris. // An accumulation of dead phagocytes, dead bacterial cells, and fluid. // Thick yellowish-white liquid typically found at sites of infection with some types of extracellular bacteria, which is composed of the remains of dead neutrophils and other cells.
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racemic mixture (racemate)
A mixture consisting of equal parts (+) and (=) enantiomers of a chiral substance; also called a racemic mixture. // An equimolar mixture of two optical isomers that does not rotate the plane of polarization of light at all. // An equimolar mixture of the D and L stereoisomers of an optically active compound.
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rate-limiting step
(1) Generally, the step in an enzymatic reaction with the greatest activation energy or the transition state of highest free energy. (2) The slowest step in a metabolic pathway. // In the series of biochemical reactions that leads to the production of a chemical, the one step that limits the rate of synthesis. // The slowest step in a multistep reaction sequence; also called the rate-determining step. The ratelimiting step acts as a kind of bottleneck in multistep reactions.
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receptor tyrosine (Tyr) kinase (RTK)
A large family of plasma membrane proteins with ligandbinding sites on the extracellular domain, a single transmembrane helix, and a cytoplasmic domain with protein Tyr kinase activity controlled by the extracellular ligand. // Cell-surface receptor with an extracellular ligand-binding domain and an intracellular kinase domain that phosphorylates signaling proteins on tyrosine residues in response to ligand binding. // Receptors that have an intrinsic tyrosine kinase activity in their cytoplasmic tails.
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recombinant DNA (rDNA) // recombinant DNA molecule
DNA formed by the joining of genes into new combinations. // A DNA molecule produced by combining DNA from two different sources. // A DNA molecule constructed in vitro by joining all or parts of two different DNA molecules.
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repressor
The protein that binds to the regulatory sequence or operator for a gene, blocking its transcription. // A DNA-binding protein that prevents transcription. // A protein that binds to DNA and turns off gene expression.
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resting membrane potential (RMP)
Electrical potential across the plasma membrane of a cell at rest, i.e. a cell that has not been stimulated to open additional ion channels than those that are normally open. // The membrane potential, or membrane voltage, maintained by a cell when it is not generating action potentials; also called resting potential. Neurons have a resting membrane potential of about –65 mV. // Voltage measured across the plasma membrane of an excitable cell at rest.
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restriction fragment
A segment of doublestranded DNA produced by the action of a restriction endonuclease on a larger DNA. // A fragment of DNA produced by cleaving a DNA molecule with one or more restriction endonucleases. // DNA fragment produced by a restriction endonuclease.
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riboswitch
A structured segment of an mRNA that binds to a specific ligand and affects the translation or processing of the mRNA. // An mRNA molecule that can regulate gene expression— transcription or translation—by undergoing a change in conformation upon binding a specific metabolite. // Part of an mRNA molecule that binds to a substrate; can change the mRNA structure and regulates synthesis of the mRNA.
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RNA primer
A short (10 to 60 nucleotides) segment of RNA that is used to initiate the synthesis of a new strand of DNA; synthesized by the enzyme DNA primase. // A short strand of RNA used to start synthesis of the lagging strand of DNA, and to start the polymerase chain reaction. // Short stretch of RNA synthesized on a DNA template. It is required by DNA polymerases to start their DNA synthesis.
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rod photoreceptor (rod)
Rod-shaped cell in retina that detects light and functions best in dim light. // A photoreceptor in the retina containing rhodopsin and specialized for low light levels. See also cone photoreceptor. // Photoreceptor cell in the vertebrate retina that is responsible for noncolor vision in dim light.
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S phase
Period of a eukaryotic cell cycle in which DNA is synthesized. // The phase of DNA replication. // The phase of the cell cycle in which the DNA genome is replicated. (Chapter 9)
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SAM // S-adenosyl methionine (adoMet)
A compound that acts as a donor of methyl groups for a number of biochemical reactions. // An enzymatic cofactor involved in methyl group transfers. // A cosubstrate that supplies an activated methyl group.
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satellite RNA // satellite
Small, single-stranded RNA molecules that lack genes required for their replication, but are replicated in the presence of another virus that can supply the required proteins (the helper virus ). (Chapter 12) // Small, single-stranded RNA molecules that lack genes required for their reproduction but do reproduce in the presence of another virus, which provides essential components (the helper virus ). (Chapter 1) // An RNA that does not encode capsid proteins, and is packaged by a protein(s) encoded in a helper virus genome. (Chapter 12)
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Secretory pathway
The organelles through which secreted proteins are processed: endoplasmic reticulum, Golgi apparatus, and secretory vesicles. // The sequential steps by which proteins and other molecules are formed wrapped in intracellular vesicles and moved toward the plasma membrane for secretion or insertion. // The series of membrane-demarcated compartments (e.g., the endoplasmic reticulum and Golgi apparatus), tubules, and vesicles through which secreted and membrane proteins travel to the cell surface. (Chapter 12)
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sepsis
Bacterial infection of the bloodstream. This is a very serious and frequently fatal condition. // The presence of a toxin or pathogenic organism in blood and tissue. // Uncontrolled, systemic infl ammation induced by infection with a pathogen. (Chapter 5)
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serum
(sēr′ŭm) Clear, watery fluid that remains after clotting proteins are removed from plasma. set point Normal value of a variable. // Blood plasma from which clotting factors have been removed. // The liquid remaining after blood plasma is clotted; contains antibodies (immunoglobulins).
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Shine-Dalgarno sequence
A sequence in an mRNA that is required for binding bacterial ribosomes. // A conserved sequence in prokaryotic mRNAs that is complementary to a sequence near the 5′ terminus of the 16S ribosomal RNA and is involved in the initiation of translation. // A ribosome-binding sequence in the 5′ untranslated region of bacterial mRNAs.
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shuttle vector
A recombinant DNA vector that can be replicated in two or more different host species. See also vector. // A plasmid that can exist in several different species; used in genetic engineering. // A plasmid capable of replicating in two different organisms, such as yeast and E. coli.
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site-directed mutagenesis
A set of methods used to create specific alterations in the sequence of a gene. // Techniques used to modify a gene in a specific location to produce the desired polypeptide. // The production of specific mutations in the test tube.
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smooth endoplasmic reticulum (smooth ER)
Region of the endoplasmic reticulum not associated with ribosomes. Involved in detoxification reactions, Ca2+ storage, and lipid synthesis. // A membrane-enclosed cellular organelle that is heterogeneous and performs different functions in different locations. // Endoplasmic reticulum without ribosomes.
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solvent
(sol′vent) Substance (e.g., water) holding a solute in solution. // A dissolving medium. // The majority component of a solution.
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Somatic hypermutation
A high frequency of mutation that occurs in the gene segments encoding the variable regions of antibodies during the differentiation of B lymphocytes into antibodyproducing plasma cells. // In immunology: accumulation of point mutations in the assembled variable-region-coding sequences of immunoglobulin genes that occurs when B cells are activated to form memory cells. Results in the production of antibodies with altered antigen-binding sites, some of which bind antigen with increased affinity; it is responsible for affinity maturation in antibody responses. // Mutations in V-region DNA of rearranged immunoglobulin genes that produce variant immunoglobulins, some of which bind antigen with a higher affinity. These mutations affect only somatic cells and are not inherited through germline transmission.
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splicing
The precise ligation of blocks of noncontiguous coding sequences (exons) in cellular or viral pre-mRNAs with excision of the intervening noncoding sequences (introns). (Chapter 10) // The process that covalently joins exon sequences of RNA and eliminates the intervening intron sequences. // The removal of nonsense RNA sequences (introns) from the RNA immediately after transcription to join portions of RNA (exons) that code for particular amino acids.
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structural gene
A gene coding for a protein or RNA molecule; as distinct from a regulatory gene. // A gene that specifies the synthesis of a polypeptide. // Gene coding for a functional, nonregulatory protein product.
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supercoiled DNA // supercoil
A DNA molecule that contains extra twists as a result of overwinding (positive supercoils) or underwinding (negative supercoils). // The twisting of a helical (coiled) molecule on itself; a coiled coil. // DNA that twists upon itself because it is under- or overwound (and thereby strained) relative to B-form DNA.
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system
An isolated collection of matter; all other matter in the universe apart from the system is called the surroundings. // Group of interacting structures working together; e.g., urinary system. // In thermodynamics, the portion of the universe that is singled out for investigation.
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TATA box
A conserved promoter sequence that determines the transcription start site. // A sequence motif in some eukaryotic promoters. // Sequence in the promoter region of many eukaryotic genes that binds a general transcription factor (TFIID) and hence specifies the position at which transcription is initiated.
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Template
A pattern or mold. DNA stores coded information and acts as a model or template from which information is copied into complementary strands of DNA or transcribed into messenger RNA. // A macromolecular mold or pattern for the synthesis of an informational macromolecule. // Single strand of DNA or RNA whose nucleotide sequence acts as a guide for the synthesis of a complementary strand.
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thermogenin
A mitochondrial uncoupling protein in brown adipose tissue. // A protein of the inner mitochondrial membrane in brown adipose tissue that allows transmembrane movement of protons, short-circuiting the normal use of protons to drive ATP synthesis and dissipating the energy of substrate oxidation as heat; also called uncoupling protein 1 (UCP1). // An uncoupling protein found in brown adipose tissue that is involved in increasing metabolism via nonshivering thermogenesis. Also known as uncoupling protein 1 (UCP1).
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thylakoid
Closed cisterna, or disk, formed by the pigment-bearing internal membranes of chloroplasts. // A chlorophyll-containing membrane in a chloroplast. A bacterial thylakoid is also known as a chromatophore. // Flattened sac of membrane in a chloroplast that contains chlorophyll and other pigments and carries out the light-trapping reactions of photosynthesis. Stacks of thylakoids form the grana of chloroplasts.
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Toll-like receptors (TLRs)
Transmembrane protein of immune cells that recognizes pathogens and activates an immune response directed against those pathogens. // Family of pattern recognition receptors (PRRs) on or in cells of the innate immune system. They recognize pathogen-associated immunostimulants (PAMPs) associated with microbes. // Innate receptors on macrophages, dendritic cells, and some other cells, that recognize pathogens and their products, such as bacterial lipopolysaccharide. Recognition stimulates the receptorbearing cells to produce cytokines that help initiate immune responses.
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Transcytosis
A mechanism of transport in which material in the intestinal lumen is endocytosed by M cells, transported to the basolateral surface, and released to the underlying tissues. (Chapter 2) // Uptake of material at one face of a cell by endocytosis, its transfer across a cell in vesicles, and discharge from another face by exocytosis. // Vesicular transport across a single-layered epithelium.
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Transfection
The uptake of DNA by a eukaryotic cell, followed by the incorporation of genetic markers present in the DNA into the cell’s genome. // Introduction of viral nucleic acid into cells by transformation, resulting in the in fection of cells. (Chapter 3) // Virus-mediated gene transfer for gene therapy.
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transformation
Introduction of an exogenous DNA into a cell, causing the cell to acquire a new phenotype. // (1) The process in which genes are transferred from one bacterium to another as “naked” DNA in solution. (2) The changing of a normal cell into a cancerous cell. // Nonselective uptake of foreign DNA by a cell.
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Transport vesicle
Membrane-bound structures with external protein coats that bud from compartments of the secretory pathway and carry cargo in anterograde or retrograde directions. (Chapter 12) // Membrane-bound sacs that move proteins from the rough ER to the Golgi complex. // Membrane-enclosed transport containers that bud from specialized coated regions of donor membrane and pass from one cell compartment to another as part of the cell’s membrane transport processes; vesicles can be spherical, tubular, or irregularly shaped.
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triglyceride
(trı̄-glis′er-ı̄d) Lipid providing long-term energy storage in adipose connective tissue; composed of glycerol and three fatty acids. // A lipid composed of one glycerol molecule bonded with three fatty acid molecules. // Triesters composed of glycerol with three fatty acids attached.
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type III secretion system (T3SS)
One of several secretion systems in Gram negative bacteria; delivers effector proteins into host cells in a contact-dependent manner. // Injection system for proteins used by Gram-negative bacteria to infect eukaryotic cells. // Specialized appendage of Gram-negative bacteria used to aid infection of eukaryotic cells by direct secretion of effector proteins into their cytoplasm.
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ubiquitin ligase
Any one of a large number of enzymes that attach ubiquitin to a protein, often marking it for destruction in a proteasome. The process catalyzed by a ubiquitin ligase is called ubiquitylation. // Enzyme that attaches ubiquitin covalently to exposed lysine residues on the surfaces of other proteins. // Enzymes that transfer ubiquitin to cellular proteins.
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variolation
An early method of vaccination using infected material from a patient. // Inoculation of healthy individuals with material from a smallpox pustule, or in modern times from a related or attenuated cowpox (vaccinia) virus preparation, through a scratch on the skin (called scarification). (Chapter 1) // The intentional inhalation of or skin infection with material taken from smallpox pustules of an infected person for the purpose of deriving protective immunity.
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viroid
Infectious RNA. // Unencapsidated, small, circular, single-stranded RNAs that replicate autonomously when inoculated into plant cells. (Chapter 1) // Unencapsidated, small, circular, single-stranded RNA molecules that replicate autonomously when introduced mechanically into host plants. (Chapter 12)
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Western blotting
Technique by which proteins are separated by electrophoresis and immobilized on a paper sheet and then analyzed, usually by means of a labeled antibody. Also called immunoblotting. // A method for the identification of separated proteins, with the use of antibodies. // A technique that uses antibodies to detect the presence of specific proteins separated by electrophoresis.
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zymogen
An inactive precursor of an enzyme; for example, pepsinogen, the precursor of pepsin. // The catalytically inactive precursor of an enzyme. // An inactive form of an enzyme, usually a protease, that must be modified in some way, for example by selective cleavage of the protein chain, before it can become active.
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β-pleated sheet
A pattern in the secondary structure of a protein that occurs when the amino acid chain is extended and forms a zigzag pattern. // A type of secondary structure of a protein. // An extended secondary structure in proteins stabilized by hydrogen bonds between polypeptides.
