Exam II Flashcards

Question

- Genome

Answer 1

the sequences of DNA that encode specific proteins and are transcribed into RNA - In humans, the gene that only encodes the major protein in hair (keratin) is expressed only in skin cells. The genetic information in the keratin-encoding gene is transcribed into RNA and then translated into a keratin polypeptide

Answer 2

are catalytic proteins that speed up biochemical reactions

Answer 3

such as antibodies recognize and respond to substances or particles that invade the organism from the environment

Answer 4

store chemical building blocks-amino acids-for later use.

Answer 5

such as collagen provide physical stability movement

Answer 6

such as hemoglobin carry substances within the organism

Answer 7

regulate when, how, and to what extent a gene is expressed Amino acids are the building blocks of proteins

Answer 8

all contain two functional groups: the nitrogen containing amino group and the carboxylic acid group. - Only 20 amino acids occur extensively in the proteins in all organisms

Answer 9

Five amino acids have electrically charged side chains (+1 or -1), attract water, and attract oppositely charged ions

Answer 10

five amino acids have polar side chains and ten to form hydrogen bonds with water and other polar or charge substances. These amino acids are also hydrophilic

Answer 11

Seven amino acids have side chains that are nonpolar hydrocarbons or very slightly modificed hydrocarbons. In the watery environment of the cell, these hydrophic side chains may cluster together in the interior of the proein. These amino acids are hydrophic

Answer 12

– three amino acids –cysteine, glycine, and prline – are special cases, although the side chains of the later two generally are hydrophix o The cystein side chain, which has a terminal –SH group, can react with another cyseine side chain to form a covalent bond called a disulfide brige. Disulfide bridges help determine how a polypeptide chain folds. o The glycine side chain consists of a single hydrogen atomn and is small enough to fit into tight corners in the interior of a protein molecule, where a larger side chain cold not fit o Proline possesses a modified amino group that lacks a hygrogen and insidead forms a covalent bond with the hydrocarbon side chain, resulting in a ring structure. This limits both its hydrogen bonding ability and its ability to rotate. Thus proline often functions to stablize bends or loops in proteins

Answer 13

amino acids can form short polymers of 20 or fewer amino acids. These include some hormones and other molecules involved in signaling from one part of an organism to another.

Answer 14

takes place in ther amino to carboxyl direction

Answer 15

a seuqnetial addition of new amino acid to the end of existing chains. The amino group of the new amino acid reacts with the carboyxl group of the amino acid at the end of the chain. This condensation reaction forms a peptide linkage.

Answer 16

the primary structure of a protein is established by covalnt bonds, but higher levels of structure are determined largely by weaker forces such as hydrogen bons and hydrophobic and hydrophilic interations

Answer 17

a proteins secondary structure consists of regular, repeated spaatial patterns in different regions of a polypeptide chain. There are two basic types of secondary structure, both determined by hydrogen bonding between the amino acid that make up the primary structure o The alpha helix - a right handed coil that turns in the same direction as a standard wood screw. The R groups extend outward from the peptide backbone of the helix. The coiling results from hydrogen bonds that form between the N-H group on one amino acid and the C=O group on another within the same turn of the helix. o The beta pleared sheet – formed from two or more polypeptide chains that are extended and aligned. The sheet is stablized by hydrogen bonds between the N-H groups and C=O groups on the two chains. A beta pleated cheet may form between separate polypeptide chains or between different regions of a single polypeptide chains that is bent back on itself.

Answer 18

Disulfide bridges can form between specific cysteine side chains, holding a folded polypeptide together. Hydrogen bonds between side chains also stablize folds in proteins. Hydrophobic side chains can aggregate together in the interior of a protein, away from water, folding the polypeptide in the process. Van der Waals internations can stablize close associations between hydrophobic side chains. Ionic interations can form between positively and negativwely charged side chains, forming salt bridges between amino acids. Inonic bonds can alos be buried deep wiuthin a protein, away from water.

Answer 19

Both secondary and tertiary structure derive from primary structure. If a protein is heated slowly, the heat will disrupt only the weaker interactions, causing the secondary and tertiary structure to break down. The protein is then said to be denatured. - In many ases the protein can return to its normal teriary structure when it cools, demonstrating that all the information needed to specify its unique shape is contained in its primary structure.

Answer 20

– many functional proteins contain two or more polypeptide chain, called subunits, each folded into its unique teriary structure. The protein’s quarternary structure results from the ways in which these subunits bind together and interact.

Answer 21

o Increases in temp causes more rapid molevular movements and thus can break hydrogen bonds and hydrophic interactions o Alterations in the concentration og H+ can change the patterns of ionization fo the exposed carboyxl and amino groups, thus disrupting the pattern of ionic attractions and repulsions o High concentrations fo polar substances such as urea can disrupt the hydrogen bonding that is crucial to protein structure o Nonpolar substances may also denature a protein in cases where hydrophic groups are essential for maintaing the protein’s structure.

Answer 22

– substances that speed up reactions without themselves being permanently altered. A catalyst does not cause a reaction to occur that would not proceed without it, but it increases the rate of the reaction. No catalyst makes a reaction occur that cannot otherwise occur. - A bio catalyst provides a molecular structure that binds the reactants and can participate in the reaction itself. This participation does not permanently change the enxyme. At the end of the reaction, the catalyst is unchanged and available to catalyze additional similar reactants

Answer 23

- Catalysts increase the rates of chemical reactions. - Most nonbiological catalysts are nonspecific. For example, powdered platinum catalyzes virtually any reactant in which molecular hydrogen is a reactant. - Most biological reactants are highly specific. - Substrated 0 reactants in an enxyme catalyzed reactions.

Answer 24

substrate molecules bindg to a particular site on the enzyme. - The specificty of an enzyme results from the exact 3d shape and chemical properties of its active site. Only a narrow range of substrates, with specific shapes, functional groups, and chemical properties, can fit properly and bind to the active site.

Answer 25

– the binding of a substrate to the active site of an enzyme produces an ES complex that is held together byu one or more means, such as h bonding, electrical attraction, or temporary covalent bonding. - The ES copmlex gives rise to product and free enzyme. - During and after the formation of the ES copmlex, chemical interactions occur. These interactions contribute directly to the breaking of old bonds and the formation of new ones. IUn catalyzing a reaction, an enxyme may use on or more mechanisms o Inducing strain – once the substrate has bound to the active site, the enzyme causes the bonds in the substrate to stretch, putting it in an unstable transition state. o Substrate orientation – When free in solutions, substrates are moving from place to place randomly while at the same time vibrating, rotationg, and tumbling. The enzyme lowers the activation energy needed to start the reaction, by bringing together specific atoms so that bonds can form o Adding chemical groups – The side chains of an enzyme’s amino acids may be directly involved in the reation. o Most for enzymes and substrates the relationship is more like a baseball and a catcher’s mitt: the substrate first binds and then the active site changes slightly to make the binding tight. o The rest of the macromolecule has at least three roles:  It provides a framework so the amino acids of the active site are properly positioned in relation to the substrate  It participates in the changes in protein shape and structure that result in induce fit  I provides binding sites for regulatory molecules.

Answer 26

Some enzymes require ions or other molecules to function

Answer 27

inorganic ions such as copper, zinc, and iron that bind to certain enzymes.

Answer 28

- For a given concentration of enzyme, the rate of the enzyme-catalyzed reaction initially increases as the substrate concentration increases from zero but then it leveles off. Why? Because the concentration of an enzyme is usually much lower than that of its substrate and does not change as substrate concentration changes. When all the enzyme molecules are bound to substrate molecules, the enzyme is working at its maximum rate. Under these conditions the active sites are said to be saturated

Answer 29

- Various chemical inhibitors can bind to enzymes, slowing down the rats of the reactions they catalyze. - Naturally occuring inhibitors regulate metaboloism

Answer 30

if an inhibitor covalently binds to an amiono acid side chain at the active site of an enxyme, the enxyme is permanently inactivated because it cannot interact with its substrate. The irreversible inhibition of enzymes is of partical use to humans, but this form of regulatiojn is not common in the cell because the enzyme is permnanently inactivated and cannot be recyled

Answer 31

– an inhibitor is similar enough toa particular enzyme’s natural substrate that it can bind noncovalently to the active site, yet different enough that no chemical reaction occurs. This is analogous to a key that inserts into a lock but does not turn it. When such a molecule is bound to the enzyme, the natural substrate cannot enter the active site and the enzyme is unable to function o Competitive inhibitor – competes with the natural substrate for the active site. o Iin this case, the inhibition is reversble. When the concentration of the competitive inhibitor is reduced, the active site is less likely to be occupied by the inhibitor

Answer 32

- The change in enzyme shape that is due to noncompetitive inhibitor binding is an example of allostery

Answer 33

occurs when a non substrate molecule binds or modifies a site other than the active site of an enzyme, inducing the enzyme to change its shape. The change in shape laters the chemical attraction of the active site for the substrate, and so the rate of the reaction is change. Allosteric regulation can result in the activation of a formerly inactive enzyme, or the inactivation of an enzyme.

Answer 34

- An enzyme can have more than one allosteric site and these may be modified by eithe covalent or noncovalent bonding o Covalent modification – an amino acid reisdue can be covalently modified by the addition of phosphate. If this occurs in a hydrophic region fo the enzyme, it makes that region hyfrophilic, because phosphate carries a negative charge. The porotein twists, and this can expose or hide trhe active site.

Answer 35

- An enzyme can have more than one allosteric site and these may be modified by eithe covalent or noncovalent bonding A regulatory molecule may bind noncovalently to an allosteric site, causing the enzyme to change shape. This can either activate or inhibit the enzyme’s function.

Answer 36

o Cells are the fundamental units of life o All living organisms are composed of cells o All cells come from preexisting cells - Studying cell biology is in some sense the same as studying life. - Life is continuous.

Answer 37

as an object increases in volume, its surface area also increases, but not as quickly. o The volume of a cell determines the amount of metabolic activity it carries out per unit of time o The surface area of a cell determines the amount of substances that can enter it from the outside environment, and the amount of waste products that can exit to the environment - As a living cell grows larger, its metabolic activity, and thus its need for resources and its rate of waste production, increases faster than its surface area/ In addition, substances must move from one location to another within the cell; the smaller the cell, the more easily this is accomplished. The large surface area to volume ratio represented by the many small cells of a multicellular organism enables it to carry out the many different functions required for survival

Answer 38

use glass lenses and visible light to form images. The smallest detail that can be seen with such a microscope is about .2u in diameter, which is about 1000 times smaller than an object the human eye can see

Answer 39

use an electron beam focused by magnets. The size limit is 2 nm, which is 100000 times smaller than something the human eye can see. Electron microscopes can be used to visualize most structures within preserved cells.

Answer 40

beings with breaking them open to make a cell free extract. This can be done physically, using a blender or other homogenizing machinery, or osmotoically, by placing the cell in a chemical environment where it swells and bursts. In either case, the resulting extract can be analyzed in terms of its composition and chemical reactions.

Answer 41

- A key to the origin of cells was the enclosure of biochemical functions within a membrane.

Answer 42

it consists of phospholipid bilayers with proteins, and that there is both compositional and functional diversity within this general framework. o The plasma membrane acts as a selectively permeable barrier, preventing some substances from crossing it while permitting other substances to enter and leave the cell. In doing so, it allows the cell to maintain homeostasis. This explains why a red blood cell contains the pigmented molecule hemoglobin but the surrounding blood plasma does not o As the cell’s boundary with the outside environment, the plasma membrane is important in communicating with adjacent cells and receiving signals from the environment. o The plasma membrane often has proteins protruding from it that are responsible for binding and adhering to adjacent cells or to a surface.

Answer 43

- Bios classify all living things into 3 domains: Archaea, Bacteria, and Eukarya.

Answer 44

The organisms in Archaea and Bacteria are collectively because they have in common a prokaryotic cellular organization. A prokaryotic cello typically does not have membrane-enclosed internal compartments; in particular, it does not have a nucleus.

Answer 45

Includes the protists, plants, fungi, and animals. The eukaryotes contain membrane enclosed compartments called organelles where specific metabolic functions occur. The most notable of these is the cell nucleus, where most of the cell’s DNA is located and where gene expression begins. Each organelle provides a compartment that separates certain molecules and biochemical reactions from the rest of the cell.

Answer 46

o The plasma membrane encloses the cell, separating its interior from the external environment, and regulates the traffic of materials into and out of the cell o The nucleoid is a region in the cell where the DNA is location. DNA is the hereditary material that controls cell growth, maintenance, and reproduction.

Answer 47

- The rest of the material enclosed in the plasma membrane is called the cytoplasm

Answer 48

consists mostly of water containing dissolved ions, small molecules, and soluble macromolecules such as proteins

Answer 49

are complexes of RNA and proteins that are about 25 nm in diameter. They can be visualized only with the electron microscope. They are the sites of protein synthesis, where the information encoded by nucleic acids directs the sequential linking of amino acids to form proteins

Answer 50

is not a static region. The substances in this environment are in constant motion.. A typical protein moves around the entire cell within a minute, and it collides with many other molecules along the way. This constant motion helps ensure that biochemical reactions proceed at sufficient rates to meet the needs of the cells.

Answer 51

Most prokaryotes have a cell wall located outside the plasma membrane. The rigidity of the cell walls supports the cell and determines its shape. The cell walls of most bacteria, but not those of Archaea, contain peptidoglycan, a polymer of amino sugars that are cross-linked by covalent bonds to peptides, forming a single giant molecule that surrounds the entire cell. In some bacteria, another layer, the outer membrane (a polysac-rich phospholipid), encloses the peptidoglycan layer. Unlike the plasma membrane, this outer membrane is relatively permeable, allowing the movement of molecules across it. Enclosing the cell wall of some bacteria is a slimy layer composed mostly of polysaccharides, referred to as the capsule. In some cases these capsules protect the bacteria from the attack by white blood cells in the animals they infect. Capsules also help keep the cells from drying out, and sometimes they help bacteria attach to other cells. Many prokaryotes produce no capsule, and those that do have capsules can survive even if they lose them

Answer 52

Some groups of bacteria-including cyanobacteria- carry out photosynthesis: they use energy from the sun to convert carbon dioxide and water into carbohydrates. These bacteria have an internal membrane system that contains molecules needed for photosynthesis.

Answer 53

Some prokaryotes swim by using appendages called flagella, which sometimes look like tiny corkscrews. In bacteria, flagella are made of a protein called flagelin. A complex motor protein spins each flagellum on its axis like a propeller, driving the cell along. The motor protein is anchored to the plasma membrane and, in some bacteria, to the outer membrane of the cell wall.

Answer 54

Some prokaryotes, especially rod-shaped bacteria have a helical network of filamentous structures that extend down the length of the cell just inside the plasma membrane. The proteins that make up this structure are similar to actin in eukaryotic cells. The helical filaments in these prokaryotes play a role in maintaining their rod like cell shape.

Answer 55

like prokaryotic cells, eukaryotic cells have a plasma membrane, cytoplasm, and ribosomes. They also have a cytoskeleton composed of protein fibers, and outside the plasma membrane, an extracellular matrix - Prokaryotic cells also have organelles within the cytoplasm

Answer 56

– are the cells power plants

Answer 57

composed of microtubules, intermediate filaments, and microfilaments supports the cell and is involved in cell and organelle movement

Answer 58

associated with nuclear division and formation of cilia

Answer 59

separates the cell from its environment and regulates traffic of materials into and out of the cell

Answer 60

the site of much protein synthesis which occurs on ribosomes on its surface

Answer 61

break down toxic peroxides

Answer 62

supports the plan cell

Answer 63

proteins and other molecules are chemically modified here

Answer 64

processes and packages proteins

Answer 65

assemble proteins

Answer 66

- Each type of organelle has a specific role in the cell. Some have been characterized as factories that make products while others are like power plants that take in energy in one form and convert it into a more useful form

Answer 67

both prokaryotes and eukaryotes consist of one larger and one smaller subunit; the size of the subunits differs between the two cell type. Each subunit consists of one to three large RNA molecules called rRNA and multiple smaller protein molecules that are bound noncovalently to one another and to the rRNA. If the individual macromolecules are separated by disruption of their hydrophobic interactions, they will spontaneously reassemble into a function complex. The role of the ribosome is to translate the nucleotide sequence of a messenger RNA molecule into a polypeptide chain. Ribosomes are not membrane enclosed compartments. In prokaryotic cells, ribosomes float freely into the cytoplasm. In eukaryotic cells they are found in the cytoplasm, where they may be free or attached to the surface of the endoplasmic reticulum and also in certain organelles such as the mitochondria and the chloroplasts

Answer 68

– it is the location of the DNA and of DNA replication. It is where DNA is transcribed to RNA. It contains the nucleolus, a region where ribosomes begin to be assembled from RNA and proteins. The nucleus is enclosed by two membranes-two lipid bilayers-that together form the nuclear envelope. This barriers separates DNA transcription from translation. The two membranes are perforated by nuclear pores and these pores regulate the traffic between these two cellular compartments by allowing some molecules to enter or leave the nucleus and by blocking others. This allows the nucleus to regulate its information-processing functions. DNA is combined with proteins to form a fibrous complex called chromatin.

Answer 69

Chromatin occurs in the form of exceedingly long, thin threads called chromosomes. Different eukaryotic organisms have different numbers of chromosomes.

Answer 70

– much of the volume of many eukaryotic cells is taken up by it. This interconnected system of membrane enclosed compartments includes the nuclear envelope, ER, Golgi apparatus, and lysosomes, which are derived from the Golgi.

Answer 71

tiny, membrane surrounded droplets shuttle between substances between the various components of the endomembrane system, as well as the plasma membrane.

Answer 72

– networks of interconnected membranes branching throughout the cytoplasm, forming tubes and flattened sacs. The interior compartment (lumen) of the ER is separate and distinct from the surrounding cytoplasm. The ER can enclose up to 10 percent of the interior volume of the cell, and its extensive folding results in a surface area many times greater than that of the plasma membrane

Answer 73

is called rough because of the many ribosomes attached to the outer surface of the membrane, giving it a rough appearance. These ribosomes are not permanently attached to the ER but become attached when they begin synthesizing proteins destined for modification within the RER. o A protein enters the RER only if it contains a specific short sequence of amino acids that signals the ribosome to attach the RER o Once inside the RER, proteins are chemically modified to alter their functions and to chemically tag them for delivery to specific cellular destinations. o The RER participates in transporting these proteins to other locations in the cell. The proteins are transported in vesicles that pinch off from the ER. All secreted proteins pass through the RER

Answer 74

that is synthesized on the RER surface is transported across the membrane and into the lumen while it is being translated. Once inside, it undergoes several changes, including the formation of disulfide bridges and folding into its tertiary structure.

Answer 75

Many proteins are covalently linked to carb groups in the RER.

Answer 76

often have roles in recognition-for example, they identify proteins destined for transfer to specific cell locations. This addressing system is very important for ensuring that proteins arrive

Answer 77

connected to portions of the RER but lacks ribosomes and is more tubular (less like flattened sacs) than the RER. Some of the proteins synthesized on the RER are transported to the lumen of the SER, where they are chemically modified. The SER has 3 other important roles o It is responsible for the chemical modification of small molecules taken in by the cell, including drugs and pesticides. These modifications make the targeted molecules more polar, so they are more water soluble and more easily removed o It is the site of glycogen degradation in animal ells o It is the site for the synthesis of lipids and steroids

Answer 78

usually packed with RER. Examples include glandular cells that secrete digestive enzymes and white blood cells that secrete antibodies. In contrast, cells that carry out less protein synthesis contain less RER. Liver cells, which modify molecules that enter body from the digestive system, have abundant SER

Answer 79

named about Camillo Golgi. It has two components: flattened membranous sacs called cisternae, which are piled up like saucers, and small membrane-enclosed vesicles. When protein-containing vesicles from the RER fuse with the Golgi membrane, the proteins are released into the lumen of a Golgi cisterna, where they may be further modified. The Golgi has several roles o It concentrates, packages, and sorts proteins before they are sent to their cellular and extra cellular destinations o It adds some carbs to proteins o It is where some polysaccharides for the plant cell wall are synthesized

Answer 80

– has three functionally distinct regions: the cis region lies nearest to the nucleus or a patch of RER, the trans region lies closest to the plasma membrane, and the medial region lies in between. Protein containing vesicles from the ER fuse with the cis membrane of the Golgi apparatus. Other vesicles may transport proteins from one cisterna to the next , although it appears that some proteins move between cisterna through tiny channels. Vesicles budding off from the trans region carry their contents away from the Golgi apparatus. These vesicles go to the plasma membrane

Answer 81

originate from the Golgi. They contain hydrolases, and they are the sites where macromolecules-proteins, polys, nucleic acids, and lipids-are hydrolyzed into their monomers. Some macromolecules that are hydrolyzed enter from the environment outside the cell by a process called phagocytosis. In this process, a pocket forms in the plasma membrane and then deepens and encloses material from outside the cell. The pocket becomes a small vesicle containing macromolecules called a phagosome, which breaks free of the plasma membrane to move into the cytoplasm. The phagosome fuses with a primary lysosome to form a secondary lysosome, in which hydrolysis occurs. The products of digestion pass through the membrane of the lysosome, providing monomers for other cellular processes. The “used” secondary lysosome, now containing undigested particles, then moves to the plasma membrane, fuses with it, and releases the undigested contents to the environment. Plant cells do not appear to contain lysosomes, but the central vacuole of a plant cell may function like it.

Answer 82

specialized calls whose major role is to take in and break down materials; They are found in nearly all animal and many protists. However, lysosomes are active even in cells that do not perform phagocytosis. All cells continually break down some of their components and replace them with new ones.

Answer 83

The programmed destruction of cell components and lysosomes are where the cell breaks down its own materials, even entire organelles, hydrolyzing their constituents. An entire class of human diseases called lysosomal storage diseases occur when lysosomes fail to digest internal components these diseases are often very harmful or fatal. An example is Tay-Sachs disease, in which particular lipid called ganglioside is not broken down in the lysosomes and instead accumulates in brain cells and damages them.

Answer 84

- Mitochondria harvest chemical energy, while chloroplasts harvest energy from sunlight

Answer 85

The breakdown of energy rich molecules such as the monosaccharide glucose begins in the cytosol.. The molecules that result from this partial degradation enter the mitochondrion, whose primary function is to convert the chemical energy of those molecules into a form the cell can use, namely the energy rich nucleotide ATP. A typical mitochondrion is about the size of many bacteria. It can divide independently of the central nucleus. The number of mitochondria per cell ranges from one gigantic organelle in some unicellular protists to a few hundred thousand in large egg cells. An average human liver cell contains more than 1000 mitochondria. Cells that are active in movement and growth require the most chemical energy, these tend to have the most mitochondria per unit of volume. Mitochondria have two membranes. The outer membrane has large pores, and most substances can pass through it. The inner membrane separates the biochemical processes of the mitochondrion from the surrounding cytosol. The inner membrane is extensively folded into structured called cristae, and the fluid filled region inside the inner membrane is referred to as the mitochondrial matrix. The mitochondrion contains many enzyme for energy metabolism, as well as DNA and ribosomes for the synthesis of a small proportion fop the mitochondrial proteins.

Answer 86

plastids are present in the cells of plants and algae, and like mitochondria, they can divide autonomously. Plastids can differentiate into a variety into of organelles, some of which are used for the storage of pigments, carbs, lipids, or proteins. An important type of plastid is the chloroplast, which contains the green pigment chlorophyll and is the site of photosynthesis.

Answer 87

an anabolic process that converts light energy into the chemical energy contained in bonds between the atoms of carbs

Answer 88

is enclosed within two membranes. It also contains a series of internal membranes that look like stacks of flat, hollow discs, called thylakoids. Each stack of thylakoids is called a granum. Light energy is converted to chemical energy on the thylakoid membranes. The aqueous fluid surrounding the thylakoids is called the stroma, and it is there that carbs are synthesized. Like the mitochondrial matrix, the chloroplast stroma contains ribosomes and DNA, which are used to synthesize some of the chloroplast proteins.

Answer 89

small organelles that accumulate toxic peroxides. Peroxides has a single membrane and a granular interior containing specialized enzymes

Answer 90

found in plants. Most abundant in young plants and are the location where stored lipids are converted into carbs for transport to growing cells

Answer 91

occur in many eukaryotic cells, but particularly those of plants and fungi. o Storage – like all cells, plant cells produce a variety of toxic by products and waste products. Plants store many of these in vacuoles. These stored toxins deter animals from eating them o Structure – enormous vacuoles take up more than 90 prevent of the cell volume and grow as the cell grows. The presence of dissolved substances in the vacuoles causes water to enter it from the cytoplasm making the vacuole swell like a water filled balloon. The plant cell wall resists the swelling causing the cell to stiffen from the pressure and this is called turgor pressure. o Reproduction – some pigments in the petals and fruits of flowering plants are contained in vacuoles. These pigments are visual cues that help attract animals o Catabolism – the seeds of some plants the vacuoles contain enzymes that hydrolyze stored seed proteins into monomers. The developing plant seedling uses these monomers as building blocks and sources of energy.

Answer 92

mesh work of protein filaments. Each filament is a polymer, made of monomers that are proteins o It supports the cell and maintains its shape o It controls the positions and movements of organelles within the cell o It is involved with bulk movements of the cytoplasm, called cytoplasmic streaming o It interacts with extracellular structures, helping to anchor the cell in place

Answer 93

are made of actin and are usually bundles. They help the entire cell or parts of the cell move and they determine and stabilize cell shape. Microfilaments are assembled from actin monomers that attach to the filament at one end (the plus end) and detach at the other (the minus end). In an intact filament, assembly and detachment are in equilibrium. But sometimes the filaments can shorten or lengthen (actin polymer \<-\> actin monomers). This property of dynamic instability is a hallmark of the cytoskeleton. Portions of it can be made and broken down rather quickly, depending on cell function. Actin associated proteins work at both ends of the filament to catalyze assembly and disassembly. In the muscle cells of animals, actin filaments are associated with another protein, the motor protein myosin, and the interactions of these two proteins account for the contraction of muscles. In nonmuscle cells, actin filaments are associated with localized changes in cell shape.

Answer 94

- There are 50 kinds of intermediate filaments. They generally fall into 6 molecular classes (based on amino sequence) that share the same general structure. One of these classes consist of fibrous proteins of the keratin family, which also includes the proteins in hair and fingernails. Intermediate filaments are more permanent than the other two types of filaments and do not show dynamic instability o They anchor cell structures in place. In some cells, intermediate filaments radiate from the nuclear envelope and help maintain the positions of the nucleus and other organelles in the cell. o They resist tension.

Answer 95

are the largest diameter components of the cytoskeletal system. They are long, hollow, unbranched cylinders. o They form rigid internal skeleton for some cells or cell regions o They act as a framework along which motor proteins move structures within the cell o Microtubules are assembled from dimers of the protein tubulin . The dimers consist of one molecule each of alpha tubulin and beta tubulin. Thirteen chains of tubulin dimers surround the hollow microtubule. They show dynamic instability. Microtubules often form an interior skeleton for projections that come out of the plasma membrane, such as cilia and flagella.

Answer 96

the cilia and the flagella. Many eukaryotic cells have one or both of these appendages, which are projections of the plasma membrane lined with microtubules and their associated proteins. Microtubules that line cilia and flagella do more than just make them rigid. They are responsible for the movement of these organelles by bending. They’re typically surrounded by the plasma membrane and contain a “9+2” array of microtubules. Nine fused pairs of microtubules (called doublets) form an outer cylinder, and one pair of unified microtubules runs up the center. A spoke radiates from one microtubule of each doublet and connects the doublet to the center of the structure. These structures are essential to the bending motions.

Answer 97

they are present by the hundreds and move stiffly to either propel a cell or to move fluid over a stationary cell

Answer 98

are long and occur singly or in pairs. They can push or pull the cell through its aqueous environment.

Answer 99

results from the sliding of the microtubule doublets past each other. This sliding is driven by a motor protein called dynein, which can change its 3d shape (all motor proteins work by undergoing reversible shape changed powered by energy). Dynein molecules bind between two neighboring microtubule doublets. As the dynein molecules change shape, they move the doublets past one another. Another protein, nexin, can cross link the doublets and prevent them from sliding past one another. Motor proteins, including kinesin, carry protein laden vesicles from one part of the cell to another. These proteins bind to a vesicle or other organelle and then walk it along a microtubule by a repeat series of shape changes. Dynein moves attached organelles toward the minus end, whole kinesin moves them toward the plus end.

Answer 100

a prominent fibrous macromolecule and a gel like medium in which the fibers are embedded

Answer 101

is a semirigid structure outside the plasma membrane. The fibrous component is the polysaccharide cellulose and the gel like matrix Is extensively cross linked polysaccharides and proteins. o It provides support for the cell and limits the volume of a mature cell by remaining rigid o It acts as a barrier to infection by fungi and other organisms that can cause plant diseases o It contributes to plant form by controlling the direction of cell expansion during growth and development o Cytoplasms of adjacent plant cells are connected by numerous plasma membrane lined channels called plasmodesmata..

Answer 102

the phospholipid bilayer serves as a lipid lake in which a variety of proteins float.

Answer 103

are attached to the outer surface of proteins forming glycoproteins or lipids forming glycolipids. They are crucial for recognizing specific molecules such as those on the surfaces of adjacent cells. Short Oligs covalently bound to proteins or lipids.

Answer 104

cross the entire phospholipid bilayer; others penetrate only partially into the bilayer

Answer 105

interspersed among phospholipid tails in the bilayer influence the fluidity of fatty acids in the membrane. Stabilizes the membrane. Breaks up hydrophobic interactions.

Answer 106

do not penetrate the bilayer at all

Answer 107

– isolate cytoplasm from external environment, transport of molecules, and cell recognition

Answer 108

in biological membranes are usually phospholipids. o Hydrophilic region – the phosphorus containing head of a phospholipid is electrically charged and therefore associates with polar water molecules o Hydrophobic regions – the long nonpolar fatty acid tails of a phospholipid associate with other nonpolar materials, but they do not dissolve in water or associate with hydrophilic substances

Answer 109

cholesterol and long chain, saturated fatty acids pack tightly together, resulting in less fluid membrane. Unsaturated fatty acids or those with shorter chains tend to increase membrane fluidity. Some anesthetics are nonpolar and act by inserting into the membrane, where they reduce the fluidity of nerve cell membranes and thereby decrease nerve activity

Answer 110

membrane fluidity declines under cold conditions because molecules move more slowly

Answer 111

lacks exposed hydrophobic groups and are not embedded in the bilayer. Instead, they have polar or charge regions that interact with exposed parts or with polar heads

Answer 112

partly embedded in the phospholipid bilayer. These proteins have both hydrophilic and hydrophobic regions - Membrane proteins and lipids generally interact only noncovalently

Answer 113

consists of a carb covalently bonded to a lipid. Extending outside the cell surface, the carb may serve as a recognition signal for interactions between cells.

Answer 114

– consists of a carb covalently bonded to a protein. The bound carb is an olig sacc of 15 or fewer monosac units. These olig often function as signaling sites as do the carbs attached to the glycolipids.

Answer 115

bio membranes allow some substances to pass through o Passive transport – do not require direct input of metabolic energy to drive them o Active transport – require the input of metabolic energy from an outside source

Answer 116

- Passive transport can occur by either simple diffusion through the phospholipid or facilitated diffusion through channel proteins or by means of carrier proteins.

Answer 117

a solution in which the solute molecules are uniformly distributed

Answer 118

– the process of random movement toward a state of equilibrium. It is the net movement from regions of greater concentration to lesser concentration. Diffusion is generally a very slow process in living tissue.

Answer 119

o Diameter of the molecules or ions: smaller molecules diffuse faster o Temperature of a solution: higher temps lead to faster diffusion because the heat provides more energy for movement o Concentration gradient –that is the change in solute concentration with distance in a given area.

Answer 120

o2, co2, no, a molecule that is hydrophobic and soluble in lipids can enter the membrane readily and pass through it. The more lipid soluble the molecule is, the more rapidly it diffuses through the lipid bilayer

Answer 121

water molecules pass through specialized channels in membranes. This process depends on the relative concentrations of water molecules on both sides of the membrane. The higher the total solute concentration, the lower the concentration of water molecules.

Answer 122

solution has a higher solute concentration than other solution

Answer 123

solutions have equal solute concentrations

Answer 124

– solution has a lower solute concentration than other solution

Answer 125

– are integral membrane proteins that form channels across the membrane through which certain substances can pass - Some substances can bind to membrane proteins called carrier proteins that speed up their diffusion through the phospholipid bilayer

Answer 126

– specific channels allow large amounts of water to move along its concentration gradient.

Answer 127

– a short stretch of amino acids that indicates where in the cell the polypeptide belongs. In the absence of a signal sequence, the protein will remain in the same cellular compartment where it is synthesized

Answer 128

the cutting of a polypeptide chain.

Answer 129

is the addition of carbs to proteins to form glycoproteins

Answer 130

the addition of phosphate groups to proteins and is catalyzed by protein kinases. The charged phosphate groups change the conformation fo the protein, often exposing the active site of an enzyme or the binding site for another protein. Phosphorylation is especially important in cell signaling

Answer 131

o Plasma membranes and ribosomes o Have a common set of metabolic pathways o Replicate as the genetic material to encode proteins, and use a similar genetic code to produce these proteins by transcription and translate - Prokaryotic cells do not divide by mitosis, instead they divide by binary fission

Answer 132

- Some prokaryotes can live only by anaerobic metabolism because oxygen is poisonous to them. The oxygen sensitive organisms are called obligate anaerobes. - Other prokaryotes can shirt their metabolism between anaerobic and aerobic modes ## Footnote

Answer 133

- The origin of a flexible surface - Origin of a cytoskeleton - Origin of a nuclear envelope which enclosed a genome organized into chromosomes - Appearance of digestive vacuole] - Acquisition of certain organelles via endosymbiosis

Exam II Flashcards

(170 cards)