Biochem Exam 2
Based on Chargaff's rules, which base compositions for double-stranded DNA are possible? %A %G %C %T %U a. 45 45 5 0 b. 20 20 20 20 20 c. All of the answers are correct. d. 35 15 35 15 0 e. None of the answers is correct.
a. 45 45 5 0
From the abbreviated name of the compound Gal(β1 → 4)Glc, we know that: a. C-4 of glucose is joined to C-1 of galactose by a glycosidic bond. b. the glucose is in its pyranose form. c. the glucose residue is the β anomer. d. the compound is a D-enantiomer. e. the galactose residue is at the reducing end.
a. C-4 of glucose is joined to C-1 of galactose by a glycosidic bond.
D-Glucose is called a reducing sugar because it undergoes an oxidation-reduction reaction at the anomeric carbon. One of the products of this reaction is: a. D-gluconate. b. muramic acid. c. D-ribose. d. D-galactose. e. D-glucuronate.
a. D-gluconate.
Which statement is FALSE? a. For S → P, a catalyst shifts the reaction equilibrium to the right. b. A reaction may not occur at a detectable rate even though it has a favorable equilibrium. c. Lowering the temperature of a reaction will lower the reaction rate. d. After a reaction, the enzyme involved becomes available to catalyze the reaction again. e. Substrate binds to an enzyme's active site.
a. For S → P, a catalyst shifts the reaction equilibrium to the right
Which statement about allosteric control of enzymatic activity is FALSE? a. Heterotropic allosteric effectors compete with substrate for binding sites. b. An effector may either inhibit or activate an enzyme. c. Binding of the effector changes the conformation of the enzyme molecule. d. Allosteric proteins are generally composed of several subunits. e. Allosteric effectors give rise to sigmoidal V0 versus [S] kinetic plots.
a. Heterotropic allosteric effectors compete with substrate for binding sites.
In a NOESY experiment, you obtain a spectrum that contains peaks along a diagonal, as well as off-diagonal peaks. Which of the following is TRUE? a. The diagonal peaks are the same as you would have obtained if you performed a one-dimensional NMR experiment. b. The off-diagonal peaks represent pairs of protons that are less than 9 Å apart. c. The off-diagonal peaks represent interactions solely from secondary structure. d. This experiment can only be done with 15N labeled proteins. e. None of the answers is correct.
a. The diagonal peaks are the same as you would have obtained if you performed a one-dimensional NMR experiment.
Which statement is TRUE of enzyme catalysts? a. They lower the activation energy for the conversion of substrate to product. b. They bind to substrates but are never covalently attached to substrate or product. c. They increase the equilibrium constant for a reaction, thus favoring product formation. d. They increase the stability of the product of a desired reaction by allowing ionizations, resonance, and isomerizations not normally available to substrates. e. To be effective, they must be present at the same concentration as their substrates.
a. They lower the activation energy for the conversion of substrate to product.
Enzyme X exhibits maximum activity at pH = 6.9. X shows a fairly sharp decrease in its activity when the pH goes much lower than 6.4. One likely interpretation of this pH activity is that: a. a His residue on the enzyme is involved in the reaction. b. a Glu residue on the enzyme is involved in the reaction. c. the enzyme is found in gastric secretions. d. the reaction relies on specific acid-base catalysis. e. the enzyme has a metallic cofactor.
a. a His residue on the enzyme is involved in the reaction.
The difference between a ribonucleotide and a deoxyribonucleotide is: a. a deoxyribonucleotide has an —H instead of an —OH at C-2. b. a deoxyribonucleotide has an —H instead of an —OH at C-3. c. a ribonucleotide has an extra —OH at C-4. d. a ribonucleotide is a pyranose, deoxyribonucleotide is a furanose. e. a ribonucleotide has more structural flexibility than deoxyribonucleotide.
a. a deoxyribonucleotide has an —H instead of an —OH at C-2.
The compound that consists of ribose linked by an N-glycosidic bond to N-9 of adenine is: a. adenosine. b. a deoxyribonucleoside. c. a purine nucleotide. d. adenosine monophosphate. e. a pyrimidine nucleotide.
a. adenosine.
One of the enzymes involved in glycolysis, aldolase, requires Zn2+ for catalysis. Under conditions of zinc deficiency, when the enzyme may lack zinc, it would be referred to as the: a. apoenzyme. b. coenzyme. c. holoenzyme. d. prosthetic group. e. substrate.
a. apoenzyme.
The nucleic acid bases: a. are roughly planar. b. are relatively hydrophilic. c. are all about the same size. d. can all stably base-pair with one another. e. absorb ultraviolet light maximally at 280 nm.
a. are roughly planar.
In competitive inhibition, an inhibitor: a. binds reversibly at the active site. b. binds at several different sites on an enzyme. c. binds covalently to the enzyme. d. binds only to the ES complex. e. lowers the characteristic Vmax of the enzyme.
a. binds reversibly at the active site.
A good transition-state analog: a. binds to the enzyme more tightly than the substrate. b. is too unstable to isolate. c. binds very weakly to the enzyme. d. binds covalently to the enzyme. e. must be almost identical to the substrate
a. binds to the enzyme more tightly than the substrate.
Blood coagulation involves: a. both zymogen activation and serine proteases b. both a kinase cascade and zymogen activation. c. a kinase cascade. d. zymogen activation. e. serine proteases.
a. both zymogen activation and serine proteases
When the linear form of glucose cyclizes, the product is a(n): a. hemiacetal. b. lactone. c. oligosaccharide. d. glycoside. e. anhydride.
a. hemiacetal.
In the purification of a protein, _____ usually occurs prior to _____. a. homogenization; chromatography b. chromatography; homogenization c. SDS-polyacrylamide gel electrophoresis; chromatography d. None of the answers is correct. e. performing an assay; homogenization
a. homogenization; chromatography
Which compound is a heteropolysaccharide? a. hyaluronate b. chitin c. glycogen d. starch e. cellulose
a. hyaluronate
What are the three essential components of a mass spectrometer? a. ion source, mass analyzer, detector b. solid-resin, ion trap, autoradiogram c. antigen coated well, ion trap, detector d. ion source, autoradiogram, detector e. solid-resin, mass analyzer, autoradiogram
a. ion source, mass analyzer, detector
Phenyl-methane-sulfonyl-fluoride (PMSF) inactivates serine proteases by binding covalently to the catalytic serine residue at the active site; this enzyme-inhibitor bond is not cleaved by the enzyme. This is an example of what kind of inhibition? a. irreversible b. noncompetitive c. mixed d. competitive e. pH inhibition
a. irreversible
The phosphodiester bonds that link adjacent nucleotides in both RNA and DNA: a. join the 3' hydroxyl of one nucleotide to the 5' hydroxyl of the next. b. are uncharged at neutral pH. c. always link A with T and G with C. d. form between the planar rings of adjacent bases. e. are susceptible to alkaline hydrolysis.
a. join the 3' hydroxyl of one nucleotide to the 5' hydroxyl of the next.
A NOESY spectrum for a protein that contains 60 amino acids would be expected to contain: a. more than 60 peaks along the diagonal and more than 60 peaks off-diagonal. b. None of the answers is correct. c. 60 peaks along the diagonal and more than 60 peaks off-diagonal. d. proton chemical shifts in the 10-11 ppm range. e. 60 peaks.
a. more than 60 peaks along the diagonal and more than 60 peaks off-diagonal.
The Lineweaver-Burk plot is used to: a. solve, graphically, for the rate of an enzymatic reaction at infinite substrate concentration. b. solve, graphically, for the ratio of products to reactants for any starting substrate concentration. c. extrapolate for the value of reaction rate at infinite enzyme concentration. d. determine the equilibrium constant for an enzymatic reaction. e. illustrate the effect of temperature on an enzymatic reaction.
a. solve, graphically, for the rate of an enzymatic reaction at infinite substrate concentration.
The biochemical property of lectins that is the basis for most of their biological effects is their ability to bind to: a. specific oligosaccharides. b. specific lipids. c. specific peptides. d. amphipathic molecules. e. hydrophobic molecules.
a. specific oligosaccharides.
Which compound is NOT a reducing sugar? a. sucrose b. fructose c. glucose d. glyceraldehyde e. ribose
a. sucrose
For enzymes in which the slowest (rate-limiting) step is the reaction Km becomes equivalent to: a. the dissociation constant, Kd, for the ES complex. b. the turnover number. c. kcat. d. the [S], where V0 = Vmax. e. the maximal velocity.
a. the dissociation constant, Kd, for the ES complex.
When two carbohydrates are epimers: a. they differ only in the configuration around one carbon atom. b. one is an aldose, the other a ketose. c. they rotate plane-polarized light in the same direction. d. they differ in length by one carbon. e. one is a pyranose, the other a furanose.
a. they differ only in the configuration around one carbon atom.
A major component of RNA but not of DNA is: a. uracil. b. guanine. c. thymine. d. adenine. e. cytosine.
a. uracil.
Which pair is anomeric? a. α-D-glucose and β-D-glucose b. D-glucose and D-fructose c. D-glucose and L-glucose d. α-D-glucose and β-L-glucose e. D-glucose and L-fructose
a. α-D-glucose and β-D-glucose
Following complete hydrolysis of a sample of glycogen and a sample of cellulose, which statement must be TRUE? a. The cellulose sample is more soluble than the glycogen sample. b. Both samples consist of a mixture of α-D-glucose and β-D-glucose. c. The glycogen sample has a higher ratio of α-D-glucose than the cellulose sample. d. The cellulose sample contains only β-D-glucose. e. The glycogen sample is more soluble than the cellulose sample.
b. Both samples consist of a mixture of α-D-glucose and β-D-glucose.
Which statement about starch and glycogen is FALSE? a. Both starch and glycogen are stored intracellularly as insoluble granules. b. Both serve primarily as structural elements in cell walls. c. Glycogen is more extensively branched than starch. c. Amylose is unbranched; amylopectin and glycogen contain many (α1 → 6) branches. e. Both are homopolymers of glucose.
b. Both serve primarily as structural elements in cell walls.
Which statement is TRUE of the binding energy derived from enzyme-substrate interactions? a. Most of it is derived from covalent bonds between enzyme and substrate. b. It is sometimes used to hold two substrates in the optimal orientation for reaction. c. It cannot provide enough energy to explain the large rate accelerations brought about by enzymes. d. Most of it is used up simply binding the substrate to the enzyme. e. It is the result of covalent bonds formed between enzyme and substrate.
b. It is sometimes used to hold two substrates in the optimal orientation for reaction.
What might be expected when comparing x-ray crystallography experiments with "light" and "heavy" versions of the same protein? The "light" protein was generated in the presence of 14N as a nitrogen source, so all amino acids contain 14N. The "heavy" protein was generated in the presence of 15N as a nitrogen source, so all amino acids contain 15N. a. Resolution will be better for the "heavy" protein, and x-rays will scatter more strongly for the "heavy" protein. b. None of the answers is correct. c. Resolution will be better for the "heavy" protein. d. X-rays will scatter more strongly for the "heavy" protein. e. Crystal formation for each will require different salt conditions.
b. None of the answers is correct.
A reaction that has a ΔG′° of 25 kJ/mol is likely to have which property? a. a slow reaction rate b. a small equilibrium constant c. a large equilibrium constant d. both a small equilibrium constant and a slow reaction rate e. both a large equilibrium constant and a slow reaction rate
b. a small equilibrium constant
The phosphodiester bond that joins adjacent nucleotides in DNA: a. is positively charged. b. associates ionically with metal ions, polyamines, and proteins. c. links C-3 of deoxyribose to N-1 of thymine or cytosine. d. Links C-2 of one base to C-3 of the next. e. is susceptible to alkaline hydrolysis.
b. associates ionically with metal ions, polyamines, and proteins.
In most cases, in order for an informational carbohydrate to become a biologically active molecule, it must: a. be an asymmetric molecule. b. be covalently joined to a protein or lipid. c. contain a reducing sugar. d. contain an O-glycosidic bond. e. be present in the extracellular matrix.
b. be covalently joined to a protein or lipid.
Which of the following is required for the purification of a protein? a. All of the answers are correct. b. both an assay that detects the presence of the protein and releasing the protein from the cell or tissue c. an assay that detects the presence of the protein d. releasing the protein from the cell or tissue e. a homogeneous source of protein
b. both an assay that detects the presence of the protein and releasing the protein from the cell or tissue
To calculate the turnover number of an enzyme, you need to know: a. the Km for the substrate. b. both the enzyme concentration and the initial velocity of the catalyzed reaction at [S] >> Km. c. the initial velocity of the catalyzed reaction at [S] >> Km. d. the initial velocity of the catalyzed reaction at low [S]. e. the enzyme concentration.
b. both the enzyme concentration and the initial velocity of the catalyzed reaction at [S] >> Km.
The experiment of Avery, MacLeod, and McCarty in which nonvirulent bacteria were made virulent by transformation was significant because it showed that: a. virulence is not determined genetically. b. genes are composed of DNA. c. bacteria can undergo transformation. d. pneumonia can be cured by transformation. e. mice are more susceptible to pneumonia than are humans.
b. genes are composed of DNA.
The reference compound for naming D and L isomers of sugars is: a. glucose. b. glyceraldehyde. c. sucrose. d. fructose. e. ribose.
b. glyceraldehyde.
The difference between thymine and uracil is: a. one hydroxyl group on the ribose ring. b. one methyl group on the pyrimidine ring. c. one methyl group on the purine ring. d. one methylene group on the pyrimidine ring. e. one amine group on the pyrimidine ring.
b. one methyl group on the pyrimidine ring.
By adding SDS (sodium dodecyl sulfate) during the electrophoresis of proteins, it is possible to: a. determine an enzyme's specific activity. b. separate proteins exclusively on the basis of molecular weight. c. determine a protein's isoelectric point. d. preserve a protein's native structure and biological activity. e. determine the amino acid composition of the protein
b. separate proteins exclusively on the basis of molecular weight.
The concept of "induced fit" refers to the fact that: a. enzyme specificity is induced by enzyme-substrate binding. b. substrate binding may induce a conformational change in the enzyme, which then brings catalytic groups into proper orientation. c. enzyme-substrate binding induces movement along the reaction coordinate to the transition state. d. enzyme-substrate binding induces an increase in the reaction entropy, thereby catalyzing the reaction. e. when a substrate binds to an enzyme, the enzyme induces a loss of water (desolvation) from the substrate.
b. substrate binding may induce a conformational change in the enzyme, which then brings catalytic groups into proper orientation.
The steady state assumption, as applied to enzyme kinetics, implies: a. the enzyme is regulated. b. the ES complex is formed and broken down at equivalent rates. c. the Km is equivalent to the cellular substrate concentration. d. Km = Ks. e. the maximum velocity occurs when the enzyme is saturated.
b. the ES complex is formed and broken down at equivalent rates.
The number of substrate molecules converted to product in a given unit of time by a single enzyme molecule at saturation is referred to as the: a. maximum velocity b. turnover number. c. Michaelis-Menten number. d. dissociation constant. e. half-saturation constant.
b. turnover number.
Allosteric enzymes: a. usually have only one active site. b. usually have more than one polypeptide chain. c. usually catalyze several different reactions within a metabolic pathway. d. usually show strict Michaelis-Menten kinetics e. are regulated primarily by covalent modification.
b. usually have more than one polypeptide chain.
Which statement about hydrogen bonding in glycogen and cellulose is TRUE? a. Extensive hydrogen bonding with water makes cellulose more soluble than glycogen. b. The hydrogen bonding in cellulose favors a helical conformation. c. Glycogen primarily forms hydrogen bonds within a single chain. d. Glycogen forms more internal H-bonds than cellulose. e. Extensive internal hydrogen bonding makes cellulose more water soluble than glycogen.
c. Glycogen primarily forms hydrogen bonds within a single chain.
_____ antibodies are heterogeneous mixtures that recognize _____. a. Polyclonal; a single epitope b. Monoclonal; a single epitope c. Polyclonal; multiple epitopes d. Polyclonal; monoclonal antibodies e. Monoclonal; multiple epitopes
c. Polyclonal; multiple epitopes
Which of the following is required when performing dialysis? a. non-porous beads b. a buffer with a higher salt concentration than the protein solution c. a semi-permeable membrane d. porous beads e. ammonium sulfate
c. a semi-permeable membrane
What would be the systematic name for an enzyme that catalyzes the following reaction? alanine + 2-oxoglutarate → pyruvate + glutamate a. pyruvate:glutamate phosphotransferase b. alanine:2-oxoglutarate ligase c. alanine:2-oxoglutarate aminotransferase d. alanine:2-oxoglutarate hydrolyase e. glutamate oxidoreductase
c. alanine:2-oxoglutarate aminotransferase
A substance that elicits the production of an antibody is a(n): a. antigen-binding site b. epitope c. antigen d. macromolecular carrier e. antiserum
c. antigen
Enzymes differ from other catalysts in that only enzymes: a. fail to influence the equilibrium point of the reaction. b. are not consumed in the reaction. c. display specificity toward a single reactant. d. lower the activation energy of the reaction catalyzed. e. form an activated complex with the reactants.
c. display specificity toward a single reactant.
To determine the isoelectric point of a protein, first establish that a gel: a. relates the unknown protein to a series of protein markers with known molecular weights, Mr. b. neutralizes all ionic groups on a protein by titrating them with strong bases. c. exhibits a stable pH gradient when ampholytes become distributed in an electric field. d. contains a denaturing detergent that can distribute uniform negative charges over the protein's surface. e. is washed with an antibody specific to the protein of interest.
c. exhibits a stable pH gradient when ampholytes become distributed in an electric field.
In a plot of l/V against 1/[S] for an enzyme-catalyzed reaction, the presence of a competitive inhibitor will alter the: a. pK of the plot. b. intercept on the l/V axis. c. intercept on the l/[S] axis. d. curvature of the plot. e. Vmax.
c. intercept on the l/[S] axis.
Vmax for an enzyme-catalyzed reaction: a. increases in the presence of a competitive inhibitor. b. generally increases when pH increases. c. is twice the rate observed when the concentration of substrate is equal to the Km. d. is unchanged in the presence of a uncompetitive inhibitor. e. is limited only by the amount of substrate supplied.
c. is twice the rate observed when the concentration of substrate is equal to the Km.
The concept of "induced fit" refers to the fact that: a. enzyme-substrate binding induces movement along the reaction coordinate to the transition state. b. when a substrate binds to an enzyme, the enzyme induces a loss of water (desolvation) from the substrate. c. substrate binding may induce a conformational change in the enzyme, which then brings catalytic groups into proper orientation. d. enzyme-substrate binding induces an increase in the reaction entropy, thereby catalyzing the reaction. e. enzyme specificity is induced by enzyme-substrate binding.
c. substrate binding may induce a conformational change in the enzyme, which then brings catalytic groups into proper orientation.
In the Watson-Crick model of DNA structure (now called B-form DNA): a. A-T pairs share three hydrogen bonds. b. the 5' ends of both strands are at one end of the helix. c. the bases occupy the interior of the helix. d. G-C pairs share two hydrogen bonds. e. a purine in one strand always hydrogen bonds with a purine in the other strand.
c. the bases occupy the interior of the helix.
Specific activity is: a. the enzyme activity in 1 mg of pure enzyme. b. the enzyme activity associated with a specific enzyme in 1 mg/mL of homogenate. c. the ratio of enzyme activity to the amount of protein in the mixture. d. the activity associated with a specific enzyme. e. a measure of the accuracy of an enzyme assay.
c. the ratio of enzyme activity to the amount of protein in the mixture.
The following data were obtained in a study of an enzyme known to follow Michaelis-Menten kinetics: V0 (mmol/L) Substrate added (μmol/min) 217 .8 325 2 433 4 488 6 647 1,000 The Km for this enzyme is approximately: a. 1 mM. b. 6 mM. c. 1000 mM. d. 2 mM. e. 4 mM.2
d. 2 mM.
An enzyme-catalyzed reaction was carried out with the substrate concentration initially a thousand times greater than the Km for that substrate. After 9 minutes, 1% of the substrate had been converted to product, and the amount of product formed in the reaction mixture was 12 μmol. If, in a separate experiment, one-third as much enzyme and twice as much substrate had been combined, how long would it take for the same amount (12 μmol) of product to be formed? a. 1.5 min b. 3 min c. 13.5 min d. 27 min e. 6 min
d. 27 min
Chargaff's rules state that in typical DNA: a. A = U. b. A = G. c. A = C. d. A + G = T + C. e. A + T = G + C.
d. A + G = T + C.
Which pair is epimeric? a. D-glucose and D-glucosamine b. D-glucose and L-glucose c. D-lactose and D-sucrose d. D-glucose and D-mannose e. L-mannose and L-fructose
d. D-glucose and D-mannose
_____ are secreted or membrane proteins that contain large numbers of O-linked oligosaccharide chains. a. Glycins b. Gangliosides c. Immunoglobulins d. Mucins e. Aminoglycans
d. Mucins
In the Watson-Crick model for the DNA double helix (B form) the A-T and G-C base pairs share which property? a. The molecular weights of the two base pairs are identical. b. The plane of neither base pair is perpendicular to the axis of the helix. c. The proton-binding groups in both base pairs are in their charged or ionized form. d. The distance between the two glycosidic (base-sugar) bonds is the same in both base pairs, within a few tenths of an angstrom. e. The number of hydrogen bonds formed between the two bases of the base pair is the same.
d. The distance between the two glycosidic (base-sugar) bonds is the same in both base pairs, within a few tenths of an angstrom.
In the Watson-Crick model for the DNA double helix, which statement is NOT true? a. The two strands have complementary sequences. b. The base-pairing occurs on the inside of the double helix. c. The double helix is right-handed. d. There are two equally sized grooves that run up the sides of the helix. e. The two strands run anti-parallel to one another.
d. There are two equally sized grooves that run up the sides of the helix.
Which statement is TRUE of enzyme catalysts? a. Their catalytic activity is independent of pH. b. They are generally equally active on D and L isomers of a given substrate. c. They can increase the equilibrium constant for a given reaction by a thousand fold or more. d. They can increase the reaction rate for a given reaction by a thousand-fold or more. e. To be effective, they must be present at the same concentration as their substrate.
d. They can increase the reaction rate for a given reaction by a thousand-fold or more.
In the Watson-Crick structure of DNA, the: a. two strands are parallel. b. adenine content of one strand must equal the thymine content of the same strand. c. purine content (fraction of bases that are purines) must be the same in both strands. d. absence of 2'-hydroxyl groups allows bases to lie perpendicular to the helical axis. e. nucleotides are arranged in the A-form.
d. absence of 2'-hydroxyl groups allows bases to lie perpendicular to the helical axis.
The diagram below is a generic example of what process? a. positive feedback b. equilibrium c. systems biology d. feedback inhibition e. catabolism
d. feedback inhibition
Which of the following monosaccharides is NOT an aldose? a. glyceraldehyde b. ribose c. glucose d. fructose e. erythrose
d. fructose
Which monosaccharides is NOT a carboxylic acid? a. 6-phospho-gluconate b. gluconate c. glucuronate d. glucose e. muramic acid
d. glucose
Hemoglobin glycation is a process where _____ is _____ attached to hemoglobin. a. N-acetyl-galactosamine; enzymatically b. galactose; nonenzymatically c. glycerol; covalently d. glucose; nonenzymatically e. glucose; enzymatically
d. glucose; nonenzymatically
The basic structure of a proteoglycan consists of a core protein and a: a. glycolipid. b. lipopolysaccharide. c. peptidoglycan. d. glycosaminoglycan. e. lectin.
d. glycosaminoglycan.
In a double-stranded nucleic acid, cytosine typically base-pairs with: a. adenosine. b. uracil. c. thymine. d. guanine. e. inosine.
d. guanine.
The DNA oligonucleotide abbreviated pATCGAC: a. has a phosphate on its 3' end. b. has seven phosphate groups. c. violates Chargaff's rules. d. has a hydroxyl at its 3' end. e. has an A at its 3' end.
d. has a hydroxyl at its 3' end.
Which glycosaminoglycan is found in the synovial fluid of joints? a. keratin sulfate b. heparan sulfate c. chondroitin sulfate d. hyaluronan e. dermatan sulfated
d. hyaluronan
In a mixture of the five proteins listed below, which should elute second in size-exclusion (gel- filtration) chromatography? a. ribonuclease A Mr = 13,700 b. cytochrome c Mr = 13,000 c. RNA polymerase Mr = 450,000 d. immunoglobulin G Mr = 145,000 e. serum albumin Mr = 68,500
d. immunoglobulin G Mr = 145,000
The role of an enzyme in an enzyme-catalyzed reaction is to: a. bind a transition state intermediate, such that it cannot be converted back to substrate. b. ensure that all of the substrate is converted to product. c. ensure that the product is more stable than the substrate. d. increase the rate at which substrate is converted into product. e. make the free-energy change for the reaction more favorable
d. increase the rate at which substrate is converted into product.
Which of the following techniques can be used to identify a target protein without the use of an antibody that recognizes that protein? a. Western blot b. UV absorbance c. Sandwich ELISA d. mass spectrometry e. Indirect ELISA
d. mass spectrometry
Which enzymes are NOT among the six internationally accepted classes of enzymes? a. hydrolases b. ligases c. oxidoreductases d. polymerases e. transferases
d. polymerases
The first step in two-dimensional gel electrophoresis generates a series of protein bands by isoelectric focusing. In a second step, a strip of this gel is turned 90 degrees, placed on another gel containing SDS, and electric current is again applied. In this second step: a. the proteins in the bands separate more completely because the second electric current is in the opposite polarity to the first current. b. the individual bands undergo a second, more intense isoelectric focusing. c. the individual bands become stained so that the isoelectric focus pattern can be visualized. d. proteins with similar isoelectric points become further separated according to their molecular weights. e. the individual bands become visualized by interacting with protein-specific antibodies in the second gel.
d. proteins with similar isoelectric points become further separated according to their molecular weights.
One method used to prevent disulfide bond interference with protein sequencing procedures is: a. removing cysteine from protein sequences by proteolytic cleavage b. protecting the disulfide bridge against spontaneous reduction to cysteine thiol groups c. cleaving proteins with proteases that specifically recognize disulfide bonds d. reducing disulfide bridges and preventing their re-formation by further modifying the —SH groups. e. sequencing proteins that do not contain cysteine residues
d. reducing disulfide bridges and preventing their re-formation by further modifying the —SH groups.
Which of the following is true of gel-filtration chromatography but not ion-exchange chromatography? a. requires beads that are covalently modified to contain an affinity group b. None of the answers is correct. c. requires a buffer system that allows the beads to maintain a charge d. requires porous beads e. requires insoluble beads
d. requires porous beads
Which of the following allows for proteins that are produced by recombinant DNA technology to be easily isolated from the other proteins in a cell? a. the use of yeast cells b. modification of the primary structure of a protein c. None of the answers is correct. d. the use of an affinity tag e. the use of bacterial cells
d. the use of an affinity tag
Cleavage of the following peptide with cyanogen bromide would result in the production of_____ smaller peptides, whereas cleavage with trypsin would result in the production of _____. Ala-Lys-Met-Glu-Asp-Cys-Ile-Phe-Met-Cys-Trp-Glu a. two, three b. three, three c. one, two d. three, two e. two, two
d. three, two
Purines have ____ ring(s), (each) containing _____ nitrogen(s), whereas pyrimidines have _____ ring(s), (each) containing _____ nitrogens. a. 2; 1; 1; 2 b. 1; 1; 1; 1 c. 1; 2; 1; 2 d. 2; 2; 1; 1 e. 2; 2; 1; 2
e. 2; 2; 1; 2
For the oligoribonucleotide pACGUAC, the nucleotide at the: a. 3' end has a phosphate at its 3' hydroxyl. b. 5' end has a 5' hydroxyl. c. 5' end is a pyrimidine. d. 3' end is a purine. e. 5' end has a phosphate on its 5' hydroxyl.
e. 5' end has a phosphate on its 5' hydroxyl.
Binding energy between an enzyme and a substrate contributes to catalysis in which way? a. Binding energy contributes to the process of induced fit between the substrate and the enzyme. b. Binding energy contributions allow for entropy reduction in the substrate-enzyme complex. c. Binding energy compensates for energy changes as a result of desolvation of the substrate. d. Binding energy provides the enzyme specificity for the substrate. e. All of the answers are correct.
e. All of the answers are correct.
Which statement about a plot of V0 versus [S] for an enzyme that follows Michaelis-Menten kinetics is FALSE? a. The shape of the curve is a hyperbola. b. As [S] increases, the initial velocity of reaction V0 also increases. c. The y-axis is a rate term with units of μm/min. d. Kmis the [S] at which V0 = 1/2 Vmax. e. At very high [S], the velocity curve becomes a horizontal line that intersects the y-axis at Km.
e. At very high [S], the velocity curve becomes a horizontal line that intersects the y-axis at Km.
Which method would be MOST useful to solve the structure of a small, soluble protein that does not easily form a repeating structure? a. electron microscopy b. mass spectrometry c. x-ray crystallography d. circular dichroism e. NMR
e. NMR
How is trypsinogen converted to trypsin? a. Trypsinogen dimers bind an allosteric modulator, cAMP, causing dissociation into active trypsin monomers. b. A protein kinase-catalyzed phosphorylation converts trypsinogen to trypsin. c. An increase in Ca2+ concentration promotes the conversion. d. Two inactive trypsinogen dimers pair to form an active trypsin tetramer. e. Proteolysis of trypsinogen forms trypsin.
e. Proteolysis of trypsinogen forms trypsin.
Which statement about enzyme-catalyzed reactions is FALSE? a. The Michaelis-Menten constant Km equals the [S] at which Vo = 1/2 Vmax. b. At saturating levels of substrate, the rate of an enzyme-catalyzed reaction is proportional to the enzyme concentration. c. The rate of a reaction decreases steadily with time as substrate is depleted. d. If enough substrate is added, the normal Vmax of a reaction can be attained even in the presence of a competitive inhibitor. e. The activation energy for the catalyzed reaction is the same as for the uncatalyzed reaction, but the equilibrium constant is more favorable in the enzyme-catalyzed reaction.
e. The activation energy for the catalyzed reaction is the same as for the uncatalyzed reaction, but the equilibrium constant is more favorable in the enzyme-catalyzed reaction.
Which statement is TRUE of the pentoses found in nucleic acids? a. C-5 and C-1 of the pentose are joined to phosphate groups. b. The pentoses are in a planar configuration. c. The bond that joins nitrogenous bases to pentoses is an O-glycosidic bond. d. The straight-chain and ring forms undergo constant interconversion. e. The pentoses are always in the β-furanose forms.
e. The pentoses are always in the β-furanose forms.
Which statement is NOT true of all naturally occurring DNA? a. The amount of A always equals the amount of T. b. Deoxyribose units are connected by 3',5'-phosphodiester bonds. c. The two complementary strands are antiparallel. d. Two hydrogen bonds form between A and T. e. The ratio A+T/G+C is constant for all natural DNAs.
e. The ratio A+T/G+C is constant for all natural DNAs.
Which amino acid is NOT capable using its side chain (R group) to participate in general acid-base catalysis? a. Asp b. Lys c. His d. Ser e. Val
e. Val
Amino acids are ampholytes because they can function as either a(n): a. transparent or a light-absorbing compound. b. standard or a nonstandard monomer in proteins. c. neutral molecule or an ion. d. polar or a nonpolar molecule. e. acid or a base.
e. acid or a base.
Michaelis and Menten assumed that the overall reaction for an enzyme-catalyzed reaction could be written as: Using this reaction, the rate of breakdown of the enzyme-substrate complex can be described by the expression: a. k1([Et] - [ES]). b. k-1[ES]. c. k2[ES]. d. k1([Et] - [ES])[S]. e. k-1[ES] + k2 [ES].
e. k-1[ES] + k2 [ES].
Enzymes are potent catalysts because they: a. are consumed in the reactions they catalyze. b. are very specific and can prevent the conversion of products back to substrates. c. drive reactions to completion while other catalysts drive reactions to equilibrium. d. increase the equilibrium constants for the reactions they catalyze. e. lower the activation energy for the reactions they catalyze.
e. lower the activation energy for the reactions they catalyze.
In the Watson-Crick model of DNA structure: a. phosphate groups project toward the middle of the helix, where they are protected from interaction with water. b. both strands run in the same direction, 3' → 5'; they are parallel. c. T can form three hydrogen bonds with either G or C in the opposite strand. d. the distance between the sugar backbone of the two strands is just large enough to accommodate either two purines or two pyrimidines. e. the distance between two adjacent bases in one strand is about 3.4 Å.
e. the distance between two adjacent bases in one strand is about 3.4 Å.
The enzyme pepsin is produced in the stomach lining initially as a _____, which requires _____ for activation in the stomach. a. phosphorylase; irreversible proteolytic cleavage b. proprotein; reversible proteolytic cleavage c. kinase; phosphorylation d. zymogen; ubiquitination e. zymogen; irreversible proteolytic cleavage
e. zymogen; irreversible proteolytic cleavage
Which pair is interconverted in the process of mutarotation? a. D-glucose and D-galactose b. D-glucose and L-glucose c. D-glucose and D-fructose d. D-glucose and D-glucosamine e. α-D-glucose and β-D-glucose
e. α-D-glucose and β-D-glucose
Starch and glycogen are both polymers of: a. β-D-glucose. b. sucrose. c. glucose1-phosphate. d. fructose. e. α-D-glucose.
e. α-D-glucose.
