Biochemistry 1 Final Test
Select the correct statements! Select one or more: a. Acidic amino acids have a net negative charge at neutral pH. b. The isoelectric point of acidic amino acids is at acidic pH. c. The isoelectric point of the acidic amino acids can be calculated as the average of their three pKa values. d. Asparagine is a acidic amino acid.
A. Acidic amino acids have a net negative charge at neutral pH. B. The isoelectric point of acidic amino acids is at acidic pH.
A sequence of amino acids in a certain protein is found to be -Ser-Gly-Pro-Gly-. The sequence is most probably part of a: Select one: a. b turn. b. parallel b sheet. c. a helix. d. a--sheet. e. antiparallel b sheet.
A. B-turn
The amino acid substitution of Val for Glu in Hemoglobin S results in aggregation of the protein. Which interactions are formed between the molecules in this case? Select one: a. hydrophobic b. ionic c. hydrogen bonding d. covalent e. disulfide
A. Hydrophobic
Select the correct statements! Select one or more: a. Neutral amino acids have no net charge at neutral pH. b. neutral amino acids have a positive and a negative charge at neutral pH. c. The isoelectric point of the neutral amino acids can be calculated as the average of their pKa values. d. Glutamine is a neutral amino acid.
A. Neutral amino acids have no net charge at neutral pH B. neutral amino acids have a positive and a negative charge at neutral pH. C. The isoelectric point of the neutral amino acids can be calculated as the average of their pKa values. D. Glutamine is a neutral amino acid.
Enzymes differ from other catalysts in that enzymes: Select one: a. usually display specificity toward a single reactant. b. fail to influence the equilibrium point of the reaction. c. form an activated complex with the reactants. d. lower the activation energy of the reaction catalyzed. e. are not consumed in the reaction.
A. usually display specificity toward a single reactant.
Which of the following statements about oligomeric proteins is false? Select one: a. Some subunits may have nonprotein prosthetic groups. b. All subunits must be identical. c. Contain more than one N-terminals d. Some oligomeric proteins can further associate into large fibers. e. Many have regulatory roles.
All subunits must be identical.
Which of the following statements are true for the isoelectric form of amino acids? Select one or more: a. All the naturally occuring amino acids have one positive and one negative charges. b. The a-amino group of all the naturally occuring amino acids has a positive charge. c. The a-carboxyl group of all the naturally occuring amino acids has a negative charge.
All the naturally occuring amino acids have one positive and one negative charges. The a-amino group of all the naturally occuring amino acids has a positive charge. The a-carboxyl group of all the naturally occuring amino acids has a negative charge.
Pair the amino acids with their character! 1. Glutamine 2. Lysine 3. Aspartate a. neutral b. acidic c. basic
1-a, 2-c, 3-b
Pair the amino acids with their character! 1. Proline 2. Arginine 3. Glutamate a. neutral b. acidic c. basic
1-a, 2-c, 3-b
In an helix, the R groups on the amino acid residues: Select one: a. stack within the interior of the helix. b. generate the hydrogen bonds that form the helix. c. are located outside of the helix spiral. d. cause only right-handed helices to form. e. alternate between the outside and the inside of the helix.
Are located outside of the helix spiral.
Which amino acid has a guanidine group in its side chain? Select one: a. Histidine b. Lysine c. Tyrosine d. Arginine e. Tryptophan
Arginine
Which of the following amino acids have a positively charged side chain at neutral pH? Select one or more: a. Arginine b. Lysine c. Glycine d. Aspartate e. Glutamate
Arginine & Lysine
Which of the following amino acids have four carbon atoms? Select one or more: a. Aspartate b. Threonine c. Asparagine d. Proline
Aspartate & Threonine & Asparagine
Which of the following amino acids have a negatively charged side chain at neutral pH? Select one or more: a. Arginine b. Alanine c. Asparagine d. Aspartate e. Glutamate
Aspartate, Glutamate
Which of the following statements about a plot of V vs. [S] for an enzyme that follows Michaelis-Menten kinetics is false? Select one: a. The y-axis is a rate term with units of mmol/min. b. The shape of the curve is a hyperbola. c. At very high [S], the velocity curve becomes a horizontal line that intersects the y-axis at KM. d. As [S] increases, the initial velocity of reaction(V) also increases. e. KM is the [S] at which V f. 1/2 Vmax.
At very high [S], the velocity curve becomes a horizontal line that intersects the y-axis at KM. 1/2 Vmax.
An octapeptide composed of four repeating glycylalanyl units has: Select one: a. a single free amino group on an alanyl residue. b. two free amino and two free carboxyl groups. c. a single free amino group on a glycyl residue and a single free carboxyl group on an alanyl residue d. two free carboxyl groups, both on glycyl residues. e. a single free amino group on an alanyl residue and a single free carboxyl group on a glycyl residue.
A single free amino group on a glycyl residue and a single free carboxyl group on an alanyl residue
In hemoglobin, the transition from T state to R state (low to high affinity) is triggered by: Select one: a. subunit dissociation. b. oxygen binding. c. Fe2+ binding. d. heme binding. e. subunit association.
B. Oxygen binding
Select the correct statements! Select one or more: a. Basic amino acids have a net positive charge at neutral pH. b. The isoelectric point of basic amino acids is at basic pH. c. The isoelectric point of the basic amino acids can be calculated as the average of their three pKa values. d. Arginine is a basic amino acid.
Basic amino acids have a net positive charge at neutral pH. The isoelectric point of basic amino acids is at basic pH. Arginine is a basic amino acid.
In competitive inhibition, an inhibitor: Select one: a. binds only to the ES complex. b. binds at several different sites on an enzyme. c. binds reversibly at the active site. d. binds covalently to the enzyme. e. lowers the characteristic Vmax of the enzyme.
Binds reversibly at the active site.
The concept of "induced fit" refers to the fact that: Select one: a. enzyme-substrate binding induces an increase in the reaction entropy, thereby catalyzing the reaction. 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 specificity is induced by enzyme-substrate binding. e. enzyme-substrate binding induces movement along the reaction coordinate to the transition state.
C. Substrate binding may induce a conformational change in the enzyme, which then brings catalytic groups into proper orientation.
Which of the following bond-pairs within a peptide backbone show free rotation around both bonds? Select one: a. C¬O and N--C b. N--Ca and N--C c. Ca--C and N--Ca d. C¬O and N--C? e. N--C and Ca--C
Ca--C and N--Ca
The backbone of two amino acid residues in a protein can be described as: Select one: a. Ca--C--N--Ca--C--N b. Ca--N--Ca--C--Ca--N--Ca--C c. Ca--N--C--C--N--Ca-- d. C--N--Ca--Ca--C--N e. Ca--Ca--C--N--Ca--Ca--C
Ca--C--N--Ca--C--N
Which statement is true? Select one or more: a. Citrate cycle cannot function in anaerobic conditions. b. Fatty acid oxidation takes place in the cytosol. c. Substrate level phosphorylation occurs both in glycolysis and in citrate cycle. d. Uncouplers of oxidative phosphorylation cause inhibition of oxidative catabolism. e. ADP activates oxidative phosphorylation as a substrate of FoF1 ATPase.
Citrate cycle cannot function in anaerobic conditions. Substrate level phosphorylation occurs both in glycolysis and in citrate cycle. ADP activates oxidative phosphorylation as a substrate of FoF1 ATPase.
Which of the following statements is false? Select one: a. a-keratin is a protein in which the polypeptides are mainly in the a-helix conformation b. Silk fibroin is a protein in which the polypeptide is almost entirely in the b conformation. c. Collagen is a protein in which the polypeptides are mainly in the a-helix conformation d. Gly residues are particularly abundant in collagen. e. Mutations in collagen have been shown to be responsible for some human diseases
Collagen is a protein in which the polypeptides are mainly in the a-helix conformation
Which of the following statements are true for the enzyme at the rate-limiting step of a metabolic pathway? Select one or more: a. Concentration of its substrate is higher than its Km value b. The measured reaction rate is close to its Vmax c. Its Vmax is higher than that of other enzymes in the pathway d. Its Km value is higher than that of other enzymes in the pathway e. Its Km value is lower than that of other enzymes in the pathway
Concentration of its substrate is higher than its Km value, The measured reaction rate is close to its Vmax
Which of the following statements is true when the rate-limiting step of a reaction pathway is inhibited? Select one: a. Concentration of the substrate at the inhibited enzyme drops b. Rate of the inhibited reaction is lower than that of the others in the pathway c. Concentration of the product at the inhibited enzyme drops d. Concentrations of the intermediers in the pathway do not change e. Steady-state flux of the pathway is unaltered
Concentration of the product at the inhibited enzyme drops
Which of the following statements is true for a reaction pathway under conditions of steady-state? Select one: a. Concentrations of intermediers are unaltered b. Vmax values of enzymes involved are equal c. Reaction rate at the rate-limiting step is the lowest d. Concentrations of intermediers are equal e. The system is in thermodynamic equilibrium
Concentrations of intermediers are unaltered
Which of the following amino acids have sulfur-containing side chains? Select one or more: a. Histidine b. Cysteine c. Metionine d. Proline e. Valine
Cysteine, Metionine
Select the correct statements! Select one: a. Leucine has two assimetrical centers. b. Only D-amino acids can be found in proteins. c. Natural amino acids are dextrorotatory. d. Glycine has no chiral center. e. Proline is not active optically.
D. Glycine has no chiral center.
In the binding of oxygen to myoglobin, the relationship between the concentration of oxygen and the fraction of binding sites occupied can best be described as: Select one: a. random. b. sigmoidal. c. linear with a positive slope. d. linear with a negative slope. e. hyperbolic.
E. Hyperbolic
The benefit of measuring the initial rate of a reaction, (V), is that at the beginning of a reaction: Select one: a. KM is the lowest at zero time, so the affinity to the substrate is maximal.. b. changes in [ES] will not influence the rate. c. the effects of allosteric modulators become negligible d. V=Vmax. e. changes in [S] are negligible, so [S] can be assumed as constant. f. varying [S] has no effect on V.
E. changes in [S] are negligible, so [S] can be assumed as constant.
Which conditions are necessary for two reactions to be enzymatically coupled? (Eact: activation energy) Select one or more: a. Both reactions include phosphoryl transfer. b. Eact of both reactions is high. c. At least one of the reactions is oxidoreduction. d. ΔG of the two reactions has different signs (one negative and one positive). e. Eact of both reactions is low.
Eact of both reactions is high. ΔG of the two reactions has different signs (one negative and one positive).
Which of the following statements is false? Select one: a. At the end of an enzyme-catalyzed reaction, the functional enzyme becomes available to catalyze the reaction again. b. For S P, a catalyst shifts the reaction equilibrium to the right. c. Substrate binds to an enzyme's active site. d. A reaction may not occur at a detectable rate even though it has a favorable equilibrium e. Lowering the temperature of a reaction will lower the reaction rate.
For S P, a catalyst shifts the reaction equilibrium to the right.
The three-dimensional conformation of a protein may be strongly influenced by amino acid residues that are very far apart in sequence. This relationship is in contrast to secondary structure, where the amino acid residues are: Select one: a. restricted to only about seven of the twenty standard amino acids found in proteins b. always side by side. c. generally on different polypeptide strands. d. generally near the polypeptide chain's amino terminus or carboxyl terminus. e. generally near each other in sequence.
Generally near each other in sequence.
Which of the following amino acids have five carbon atoms? Select one or more: a. Glutamate b. 2: Glutamine c. 3. Histidine d. 4. Proline e. 5.Glycine
Glutamate & 2: Glutamine & 4: Proline
Select the correct statements! Select one or more: a. Glutamate has a negative charge on its side chain at the isoelectric pH. b. Glutamate has a negative charge on its side chain at neutral pH. c. Arginine has a positive charge on its side chain at the isoelectric pH. d. Arginine has a positive charge on its side chain at neutral pH.
Glutamate has a negative charge on its side chain at neutral pH. Arginine has a positive charge on its side chain at the isoelectric pH. Arginine has a positive charge on its side chain at neutral pH.
Which of the following amino acid side chains are polar? Select one or more: a. Glutamine b. Leucine c. Asparagine d. Threonine
Glutamine & Asparagine & Threonine
Of the 20 standard amino acids, only ___________ is not optically active. The reason is that its side chain ___________. Select one: a. alanine; is a simple methyl group b. glycine; is a hydrogen atom. c. glycine; is unbranched. d. lysine; contains only nitrogen. e. proline; forms a covalent bond with the amino group.
Glycine; is a hydrogen atom.
Which statement is true regarding the group transfer potential (gtp)? Select one or more: a. Gtp is the absolute value of the ΔG of hydrolysis (when the group is released). b. Functional groups have a natural tendency to move from the lower toward the higher gtp. c. Functional groups have a natural tendency to move from the higher toward the lower gtp. d. ΔG of a group transfer equals the gtp of the group acceptor plus the gtp of the group donor. e. ΔG of a group transfer equals the gtp of the group acceptor minus the gtp of the group donor.
Gtp is the absolute value of the ΔG of hydrolysis (when the group is released). Functional groups have a natural tendency to move from the higher toward the lower gtp. ΔG of a group transfer equals the gtp of the group acceptor minus the gtp of the group donor.
For amino acids with neutral side chain, at any pH below the pI of the amino acid, the population of amino acids in solution will: Select one: a. have a net positive charge. b. have no charged groups. c. have no net charge. d. have positive and negative charges in equal concentration. e. have a net negative charge.
Have a net positive charge
Which of the following statements about allosteric control of enzymatic activity is false? Select one: a. Allosteric proteins are generally composed of several subunits. b. Heterotropic allosteric effectors compete with substrate for binding sites. c. Binding of the effector changes the conformation of the enzyme molecule. d. An effector may either inhibit or activate an enzyme. e. Homotropic allosteric effectors do not have a separate binding site.
Heterotropic allosteric effectors compete with substrate for binding sites.
Which of the following statements about proteins is true? Select one: a. Proteins that contain a-helical regions never contain b--sheets b. Proteins are generally very loosely structured. c. In water-soluble proteins, hydrophobic (nonpolar) amino acid residues are generally buried and not exposed to water. d. Detergents (such as sodium dodecyl sulfate, SDS) will not affect the structure of a protein that contains disulfide (--S--S--) bonds. e. Hydrogen bonds are not important in the structure of proteins.
In water-soluble proteins, hydrophobic (nonpolar) amino acid residues are generally buried and not exposed to water.
To calculate the turnover number of an enzyme you need to know the: Select one or more: a. initial velocity of the catalyzed reaction at low [S]. b. initial velocity of the catalyzed reaction at [S] >> KM. c. KM for the substrate. d. enzyme concentration.
Initial velocity of the catalyzed reaction at [S] >> KM. Enzyme concentration.
Specific enzyme activity: Select one: a. is the enzyme activity (expressed as ``units'') of a specific protein. b. is the enzyme activity (enzyme as ``units'') in a milligram of protein. c. is the enzyme activity (expressed as ``units'') in a mol of protein. d. refers to proteins other than enzymes. e. refers only to purified proteins.
Is the enzyme activity (enzyme as ``units'') in a milligram of protein.
Vmax for an enzyme-catalyzed reaction: Select one: a. is unchanged in the presence of a uncompetitive inhibitor. b. increases in the presence of a competitive inhibitor. c. is twice the rate observed when the concentration of substrate is equal to the KM d. generally increases when pH increases. e. is limited only by the amount of substrate supplied.
Is twice the rate observed when the concentration of substrate is equal to the KM
Which of the following is not correct concerning 2,3-bisphosphoglycerate (BPG)? Select one: a. It is normally found associated with the hemoglobin molecules that are extracted from red blood cells. b. It decreases the affinity of hemoglobin for oxygen. c. It binds to the heme groups of hemoglobin. d. It is an allosteric modulator. e. It binds with lower affinity to fetal hemoglobin than to adult hemoglobin.
It binds to the heme groups of hemoglobin.
Which statement is true regarding the oxidative decarboxylation of pyruvate in human cells? Select one or more: a. It cannot occur in anaerobic conditions. b. It is catalyzed by an enzyme complex in the cytosol. c. It is an irreversible reaction and it cannot be undone (i.e. pyruvate cannot be regenerated from the products). d. It yields FADH2, which can deliver electrons to complex II of the respiratory chain. e. It converts a glucoplastic to a ketoplastic molecule.
It cannot occur in anaerobic conditions. It is an irreversible reaction and it cannot be undone (i.e. pyruvate cannot be regenerated from the products). It converts a glucoplastic to a ketoplastic molecule.
Which statement is false regarding oxidative decarboxylation of pyruvate in human cells? Select one or more: a. It is an irreversible reaction but it can be undone (i.e. pyruvate can be regenerated from the products) by other enzymes. b. It is catalyzed by a large enzyme complex (E1, E2 and E3) in the cytosol. c. The process can occur in anaerobic conditions because the complex does not use O2. d. It belongs to substrate level phosphorylation because an ATP is produced. e. The prosthetic group of E1 is biotin, which is reoxidized by E3 in each catalytic cycle.
It is an irreversible reaction but it can be undone (i.e. pyruvate can be regenerated from the products) by other enzymes. It is catalyzed by a large enzyme complex (E1, E2 and E3) in the cytosol. The process can occur in anaerobic conditions because the complex does not use O2. It belongs to substrate level phosphorylation because an ATP is produced. The prosthetic group of E1 is biotin, which is reoxidized by E3 in each catalytic cycle.
Which statement is false regarding oxidative decarboxylation of pyruvate in human cells? Select one or more: a. It is catalyzed by homodimers of pyruvate decarboxylase in the mitochondrial matrix. b. The acetaldehyde intermediate is covalently bound to the enzyme as a hydroxyethyl group. c. The product, acetate is bound to CoA in a macroergic thioester bond. d. It is coupled to the mitochondrial electron transfer chain by NAD+ and NADH. e. It is the last step of anaerobic glycolysis and it produces lactate.
It is catalyzed by homodimers of pyruvate decarboxylase in the mitochondrial matrix. It is the last step of anaerobic glycolysis and it produces lactate.
Which statement is false regarding glycolysis? Select one or more: a. Its committed step is catalyzed by hexokinase or glucokinase. b. The whole pathway takes place in the cytosol. c. The whole pathway is reversible. d. It only evolved in higher eukaryotes (including humans). e. Its second phase yields 4 ATP and 2 NADH per glucose molecules.
Its committed step is catalyzed by hexokinase or glucokinase. The whole pathway is reversible. It only evolved in higher eukaryotes (including humans).
Which of the following amino acids have six carbon atoms? Select one or more: a. Leucine b. Isoleucine c. Histidine d. Proline e. Glycine
Leucine & Isoleucine & Histidine
The double-reciprocal transformation of the Michaelis-Menten equation, also called the Lineweaver-Burk plot, is given by 1/V = KM /(Vmax[S]) + 1/Vmax. To determine KM from a double-reciprocal plot, you would: Select one: a. multiply the reciprocal of the x-axis intercept by -1. b. take the reciprocal of the x-axis intercept. c. take the x-axis intercept where V=Vmax/2 d. multiply the reciprocal of the y-axis intercept by -1. e. take the reciprocal of the y-axis intercept. f. multiply the reciprocal of the y-axis intercept by -1
Multiply the reciprocal of the x-axis intercept by -1.
In a highly basic solution, pH = 13, the dominant form of glycine is: Select one: a. NH2--CH2--COO-. b. NH2--CH2--COOH. c. NH3+--CH2--COOH. d. NH3+--CH2--COO-. e. NH2--CH3+--COO-.
NH2--CH2--COO-.
What is the dominant form of Glycin at low pH (pH=1)? Select one: a. NH2--CH2--COO- b. NH3+--CH2--COOH c. NH3+--CH2--COO- d. NH2--CH2--COOH e. NH2--CH3+--COO-
NH3+--CH2--COOH
Which of the following statements about proteins is false? Select one: a. Nonpolar amino acid side chains are mostly located on the surface of the water soluble proteins. b. Most of the globular proteins are compact. c. Proteins are sometimes conjugated with carbohydrates or fats. d. Many proteins have more then one polypeptides . e. proteins consist of amino acids linked by peptide bonds.
Nonpolar amino acid side chains are mostly located on the surface of the water soluble proteins.
Which conditions rule out the enzymatic coupling of two reactions? (Eact: activation energy) Select one or more: a. One of the reactions has low Eact. b. Eact of both reactions is high. c. ΔG of both reactions is negative. d. ΔG of the two reactions has different signs (one negative and one positive). e. One of the reactions is oxidoreduction.
One of the reactions has low Eact. ΔG of both reactions is negative.
What is the dominant form of glutamate at pH 7.0? (pKa values of glutamate are 2.2, 3.6 and 9.2).
One positive and two negative charges
Which statement is true? Select one or more: a. Oxidative phosphorylation is activated by ATP in starvation. b. Oxidative catabolic processes in the mitochondrial matrix are coupled to respiration. c. Citrate cycle is inhibited by high NADH/NAD+ ratio. d. Pyruvate dehydrogenase is activated by low ATP/ADP ratio. e. Malate/aspartate shuttle transports electrons from fatty acid oxidation to respiration.
Oxidative catabolic processes in the mitochondrial matrix are coupled to respiration. Citrate cycle is inhibited by high NADH/NAD+ ratio. Pyruvate dehydrogenase is activated by low ATP/ADP ratio.
Which statement is true? Select one or more: a. Oxidative catabolism is driven by the low redox potential of molecular O2. b. Oxidative catabolism is driven by the high redox potential of molecular O2. c. Nutrient catabolism provides electrons for reductive biosynthesis. d. Fuel molecules can be oxidized by the addition of H atoms. e. Fuel molecules can be oxidized by the removal of H atoms.
Oxidative catabolism is driven by the high redox potential of molecular O2. Nutrient catabolism provides electrons for reductive biosynthesis. Fuel molecules can be oxidized by the removal of H atoms.
Amino acid residues commonly found at the end of b turn are: Select one: a. Pro and Gly. b. Ala and Gly. c. two Cys. d. hydrophobic. e. those with ionized R groups.
Pro and Gly.
How is trypsinogen converted to trypsin? Select one: a. Proteolysis of trypsinogen forms trypsin. b. Two inactive trypsinogen dimers pair to form an active trypsin tetramer. c. An increase in Ca2+ concentration promotes the conversion. d. Trypsinogen dimers bind an allosteric modulator, cAMP, causing dissociation into active trypsin monomers. e. A protein kinase-catalyzed phosphorylation converts trypsinogen to trypsin.
Proteolysis of trypsinogen forms trypsin.
A transition-state analog: Select one: a. resembles the active site of general acid-base enzymes. b. typically reacts more rapidly with an enzyme than the normal substrate. c. is less stable when binding to an enzyme than the normal substrate. d. stabilizes the transition state for the normal enzyme-substrate complex. e. resembles the transition-state structure of the normal enzyme-substrate complex
Resembles the transition-state structure of the normal enzyme-substrate complex
By adding SDS (sodium dodecyl sulfate) during the electrophoresis of proteins, it is possible to: Select one: a. preserve a protein's native structure and biological activity b. separate proteins exclusively on the basis of molecular weight. c. determine a protein's isoelectric point. d. determine the amino acid composition of the protein. e. determine an enzyme's specific activity.
Separate proteins exclusively on the basis of molecular weight.
Which of the amino acids below have a small polar side chain containing a hydroxyl group? Select one or more: a. Glycine b. Serine c. Threonine d. Lysine e. Leucine
Serine & Threonine
To alter the shape of the a-keratin chains--as in hair waving-- the a-keratin chains have undergone one chemical step resulting the conversion of disulfid bridges to Cysteins. What subsequent steps are required? Select one: a. chemical reduction and then chemical oxidation b. chemical oxidation and then shape remodeling c. shape remodeling and then chemical reduction d. shape remodeling and then chemical oxidation e. chemical reduction and then shape remodeling
Shape remodeling and then chemical oxidation
The Lineweaver-Burk plot is used to: Select one: a. illustrate the effect of temperature on an enzymatic reaction. b. solve, graphically, for the rate of an enzymatic reaction at infinite substrate concentration. c. determine the equilibrium constant for an enzymatic reaction. d. solve, graphically, for the ratio of products to reactants for any starting substrate concentration. e. extrapolate for the value of reaction rate at infinite enzyme concentration.
Solve, graphically, for the rate of an enzymatic reaction at infinite substrate concentration.
Which of the following describes the overall three-dimensional folding of a polypeptide? Select one: a. primary structure b. secondary structure c. tertiary structure d. quaternary structure e. none of the above
Tertiary structure
Which of these statements about enzyme-catalyzed reactions is false? Select one: a. 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. b. At saturating levels of substrate, the rate of an enzyme-catalyzed reaction is proportional to the enzyme concentration. c. The Michaelis-Menten constant (Km) equals the [S] at which V d. 1/2 Vmax. e. If enough substrate is added, the normal Vmax of a reaction can be attained even in the presence of a competitive inhibitor. f. The rate of a reaction decreases steadily with time as substrate is depleted.
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. 1/2 Vmax.
An allosteric interaction between a ligand and a protein is one in which: Select one: a. two different ligands can bind to the same binding site. b. the binding of the ligand to the protein is covalent. c. multiple molecules of the same ligand can bind to the same binding site. d. the binding of a molecule to a binding site affects the binding of an additional molecule to the same site. e. the binding of a molecule to its binding site affects the binding properties of another site on the same protein.
The binding of a molecule to its binding site affects the binding properties of another site on the same protein.
Which statement is true? Select one or more: a. The carbon atoms of glucose and fatty acids are oxidized to CO2 in the body. b. The electrons of fuel molecules are transferred to O2 by electron carriers. c. Nutrient catabolism provides electrons for reductive biosynthesis. d. Oxidative catabolism is driven by the high redox potential of molecular O2. e. Fuel molecules can be oxidized by the removal of H atoms.
The carbon atoms of glucose and fatty acids are oxidized to CO2 in the body. The electrons of fuel molecules are transferred to O2 by electron carriers., Nutrient catabolism provides electrons for reductive biosynthesis. Oxidative catabolism is driven by the high redox potential of molecular O2. Fuel molecules can be oxidized by the removal of H atoms.
What is the dominant form of Histidine at pH 8.0? (pKa values of Histidine are 1.8, 6.0 and 9.2).B:Two positive and one negative charges Select one: a. One positive and one negative charges b. Two negative and one positive charges c. One negative charge d. One positive charge
The correct answer is: One positive and one negative charges
For enzymes in which the slowest (rate-limiting) step is the reaction k2 ES ® PKM becomes equivalent to: Select one: a. kcat. b. the turnover number. c. the dissociation constant(Kd) for the ES complex. d. the [S] where V e. Vmax. f. the maximal velocity.
The dissociation constant(Kd) for the ES complex. Vmax.
A metabolic pathway proceeds according to the scheme, R ®--S ® T ® U ® V ® W.A regulatory enzyme, X, catalyzes the first reaction in the pathway. Which of the following is most likely correct for this pathway? Select one: a. The first product S, is probably the primary negative modulator of X, leading to feedback inhibition b. The last reaction will be catalyzed by a second regulatory enzyme. c. Either metabolite U or V is likely to be a positive modulator, increasing the activity of X. d. The last product, W, is likely to be a negative modulator of X, leading to feedback inhibition. e. The last product, W, is likely to be a positive modulator, increasing the activity of X.
The last product, W, is likely to be a negative modulator of X, leading to feedback inhibition.
Which statement is false regarding the group transfer potential (gtp)? Select one or more: a. The molecule of the lowest gtp is suitable as a group carrier. b. Functional groups have a natural tendency to move from the lower toward the higher gtp. c. ΔG of a group transfer equals the gtp of the group donor minus the gtp of the group acceptor. d. Low gtp means that the group is attached to the molecule with a weak bond. e. High gtp indicates a great tendency of the molecule to accept the group.
The molecule of the lowest gtp is suitable as a group carrier. Functional groups have a natural tendency to move from the lower toward the higher gtp. ΔG of a group transfer equals the gtp of the group donor minus the gtp of the group acceptor. Low gtp means that the group is attached to the molecule with a weak bond. High gtp indicates a great tendency of the molecule to accept the group.
Which input path of a branched metabolic pathway is more relevant physiologically? Select one: a. The one that has the highest metabolic flux in vivo b. The one that has the enzyme with the highest Vmax c. The one that has the enzyme with the lowest Km d. The one that has lower number of enzymatic steps involved e. The one that has the highest in vivo substrate concentration at the first enzymatic reaction
The one that has the highest metabolic flux in vivo
Kendrew's studies of myoglobin structure demonstrated that: Select one: a. "corners" between a-helical regions invariably contained a glycine residue, which, because of its unique properties, cannot fit into the helix b. the a--helix predicted by Pauling and Corey was not found in myoglobin; b-pleated sheet structure was found. c. the structure was very compact, with virtually no internal space available for water molecules. d. highly polar or charged amino acid residues tended to be located at the interior of the protein. e. the structure of myoglobin proved to be completely different from that of hemoglobin, as expected from their very different biological roles.
The structure was very compact, with virtually no internal space available for water molecules.
At the isoelectric pH of a tetrapeptide: Select one: a. there are four ionic charges b. the amino and carboxyl termini are not charged. c. two internal amino acids of the tetrapeptide cannot have ionizable R groups. d. the total net charge is zero. e. only the amino and carboxyl termini contribute charge.
The total net charge is zero.
Which statement is true regarding glycolysis? Select one or more: a. It only evolved in higher eukaryotes (including humans). b. The whole pathway takes place in the cytosol. c. Its enzymes are present in all human cells. d. Its first phase consumes 2 ATP per glucose molecules. e. Its second phase yields 4 ATP and 4 NADH per glucose molecules.
The whole pathway takes place in the cytosol. Its enzymes are present in all human cells. Its first phase consumes 2 ATP per glucose molecules.
Which statement is true regarding glycolysis? Select one or more: a. The whole pathway takes place in the cytosol. b. The whole pathway is reversible. c. Its second phase includes 2 kinase and 1 dehydrogenase enzymes. d. Its first phase consumes 2 ATP per glucose molecules. e. Its committed step is catalyzed by hexokinase or glucokinase.
The whole pathway takes place in the cytosol. Its second phase includes 2 kinase and 1 dehydrogenase enzymes. Its first phase consumes 2 ATP per glucose molecules.
Which statement is true regarding the oxidative decarboxylation of pyruvate? Select one or more: a. It belongs to substrate level phosphorylation because an ATP is produced. b. The whole process is catalyzed by an enzyme complex in the mitochondrial matrix. c. Its enzymes are present in all human cells. d. Human pyruvate decarboxylase contains biotin prosthetic group. e. It yields NADH, which can deliver electrons to complex I of the respiratory chain
The whole process is catalyzed by an enzyme complex in the mitochondrial matrix. It yields NADH, which can deliver electrons to complex I of the respiratory chain.
Which of the following statements is true of enzyme catalysts? Select one: a. They increase the equilibrium constant for a reaction, thus favoring product formation. b. To be effective they must be present at the same concentration as their substrates. c. They lower the activation energy for the conversion of substrate to product. d. They increase the stability of the product of a desired reaction by allowing ionizations, resonance, and isomerizations not normally available to substrates. e. They bind to substrates, but are never covalently attached to substrate or product.
They lower the activation energy for the conversion of substrate to product.
Which of the following statements about formation of cystine is correct? Select one: a. There is a peptide linkage between two cysteines. b. Two --CH2--SH groups are oxidized to form a --CH2--S--S--CH2-- disulfide bridge between two cysteines c. Two cystines are released when a --CH2--S--S--CH2-- disulfide bridge is reduced to --CH2--SH. d. Cystine is an example of a nonstandard amino acid, derived by linking two different standard amino acids. e. Cystine is formed by the oxidation of the carboxylic acid group on cysteine.
Two --CH2--SH groups are oxidized to form a --CH2--S--S--CH2-- disulfide bridge between two cysteines
What is the dominant form of Arginine at pH 6.0? (pKa values of Arginine are 2.2, 9.0 and 12.5).
Two positive and one negative charges
Which statement is false? Select one or more: a. Substrate level phosphorylation occurs both in glycolysis and in citrate cycle. b. Uncouplers of oxidative phosphorylation cause inhibition of oxidative catabolism. c. Pyruvate dehydrogenase and citrate cycle cannot function in anaerobic conditions. d. ADP activates oxidative phosphorylation as a substrate of FoF1 ATPase. e. FoF1 ATPase is an active transporter, which can pump protons into the matrix.
Uncouplers of oxidative phosphorylation cause inhibition of oxidative catabolism. FoF1 ATPase is an active transporter, which can pump protons into the matrix.
Which of the following amino acid side chains are nonpolar? Select one or more: a. Valine b. Leucine c. Asparagine d. Lysine
Valine & Leucine
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: Select one: a. the enzyme is found in gastric secretions b. a Lysine residue on the enzyme is involved in the reaction. c. a Glutamate residue on the enzyme is involved in the reaction. d. a Histidine residue on the enzyme is involved in the reaction. e. the enzyme has a metallic cofactor.
a Histidine residue on the enzyme is involved in the reaction.
A D-amino acid would interrupt an a helix made of L-amino acids. Another naturally occurring constraint on the formation of an a helix is the presence of: Select one: a. a negatively charged Arginine residue. b. a positively charged Lysine residue. c. two Glycine residues side by side. d. a nonpolar residue near the carboxyl terminus. e. a Proline residue.
a Proline residue.
Lysine at its isoelectric point has.... Select one: a. a deprotonated a-carboxyl group, a deprotonated--a-amino group and a protonated e-amino group. b. a deprotonated a-carboxyl group, a protonated a-amino group and a deprotonated e-amino group. c. a protonated a-carboxyl group, a protonated a-amino group and a deprotonated e-amino group. d. a protonated a-carboxyl group, a deprotonated a-amino group and a protonated--e-amino group. e. a deprotonated a-carboxyl group, a deprotonated a-amino group and a deprotonated e-amino group.
a deprotonated a-carboxyl group, a deprotonated--a-amino group and a protonated e-amino group.
A small molecule that decreases the activity of an enzyme by binding to a site other than the catalytic site is termed a: Select one: a. stereospecific agent. b. alternative inhibitor. c. allosteric inhibitor. d. competitive inhibitor. e. transition-state analog.
allosteric inhibitor
A good transition-state analog: Select one: a. binds to the enzyme more tightly than the substrate. b. binds covalently to the enzyme. c. is too unstable to isolate. d. binds very weakly to the enzyme. e. does not react with the native enzyme
binds to the enzyme more tightly than the substrate.
In a plot of l/V against 1/[S] for an enzyme-catalyzed reaction, the presence of a competitive inhibitor will alter the: Select one: a. curvature of the plot. b. intercept on the l/V axis. c. Vmax. d. intercept on the l/[S] axis. e. pK of the plot.
intercept on the l/[S] axis.
The chirality of an amino acid results from the fact that its a--carbon: Select one: a. is bonded to four different chemical groups. b. is a carboxylic acid. c. is symmetric. d. is in the L absolute configuration in naturally occurring proteins. e. has no net charge.
is bonded to four different chemical groups.
The arginyllysylaspartate tripeptide has Select one or more: a. its isoelectric point at basic pH. b. three positive and two negative charges at neutral pH. c. two positive and two negative charges at its isoelectric point.
its isoelectric point at basic pH. three positive and two negative charges at neutral pH. two positive and two negative charges at its isoelectric point.
In the a helix the hydrogen bonds: Select one: a. occur only between some of the amino acids of the helix. b. occur mainly between electronegative atoms of the R groups. c. are perpendicular to the axis of the helix. d. occur mainly between electronegative atoms of the backbone. e. occur only near the amino and carboxyl termini of the helix.
occur mainly between electronegative atoms of the backbone.
Thr and/or Leu residues tend to disrupt an a helix when they occur next to each other in a protein because: Select one: a. of the possible covalent interactions between the Thr and/or Leu side chains. b. both amino acids are highly hydrophobic. c. the R group of neither amino acid can form a hydrogen bond. d. of electrostatic repulsion between the Thr and/or Leu side chains. e. of steric hindrance between the bulky Thr and/or Leu side chains.
of steric hindrance between the bulky Thr and/or Leu side chains.
When oxygen binds to a heme-containing protein, the two open coordination bonds of Fe2+ are occupied by: Select one: a. two O2 molecules. b. two O atoms. c. one O2 molecule and one heme atom. d. one O2 molecule and one amino acid atom. e. one O atom and one amino acid atom.
one O2 molecule and one amino acid atom.
Both water and glucose share an --OH that can serve as a substrate for a reaction with the terminal phosphate of ATP catalyzed by hexokinase. Glucose, however, is about a million times more reactive as a substrate than water. The best explanation is that: Select one: a. the larger glucose binds better to the enzyme; it induces a conformational change in hexokinase that brings active-site amino acids into position for catalysis. b. glucose has more --OH groups per molecule than does water. c. water normally will not reach the active site because it is hydrophobic. d. water and ATP compete for the active site resulting in a competitive inhibition of the enzyme. e. the --OH group of water is attached to an inhibitory H atom while the glucose --OH group is attached to C.
the larger glucose binds better to the enzyme; it induces a conformational change in hexokinase that brings active-site amino acids into position for catalysis.
At neutral pH a tetrapeptide of glycylalanylarginylglutamate has... Select one: a. two positive and three negtive charges b. two positive and one negative charges c. one positive and one negative charges d. one positive and two negative charges e. two positive and two negative charges
two positive and two negative charges
Myoglobin and the subunits of hemoglobin have: Select one: a. no obvious structural relationship. b. very similar primary structures, but different tertiary structures. c. very similar primary and tertiary structures. d. very different primary and tertiary structures. e. very similar tertiary structures, but different primary structures.
very similar tertiary structures, but different primary structures.
Which statement is false regarding the group transfer potential (gtp)? Select one or more: a. ΔG of a group transfer equals the gtp of the group acceptor plus the gtp of the group donor. b. Functional groups have a natural tendency to move from the higher toward the lower gtp. c. Low gtp means that the group is attached to the molecule with a weak bond. d. High gtp indicates a great tendency of the molecule to accept the group. e. Gtp is the absolute value of the ΔG of hydrolysis (when the group is released).
ΔG of a group transfer equals the gtp of the group acceptor plus the gtp of the group donor. Low gtp means that the group is attached to the molecule with a weak bond. High gtp indicates a great tendency of the molecule to accept the group.