Midterm I

Question 1

A part of the carbon skeleton of which amino acids may enter the citric acid cycle in the form of succinyl-CoA?

Select one or more:
A. Isoleucine
B. Leucine
C. Tyrosine
D. Proline
E. Valine

Answer 1

A. Isoleucine
E. Valine

Question 2

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

Answer 2

b. Serine
c. Threonine

Question 3

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

Answer 3

a. Arginine
b. Lysine

Question 4

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

Answer 4

d. Aspartate
e. Glutamate

Question 5

Which of the following amino acids have sulfur-containing side chains?

Select one or more:

a. Histidine
b. Cysteine
c. Methionine
d. Proline
e. Valine

Answer 5

b. Cysteine
c. Methionine

Question 6

Which of the following amino acids have four carbon atoms?

a. Aspartate
b. Threonine
c. Asparagine
d. Proline

Answer 6

a. Aspartate
b. Threonine
c. Asparagine

Question 7

Which of the following amino acids have five carbon atoms?

Select one or more:

a. Glutamate
b. Glutamine
c. Histidine
d. Proline
e. Glycine

Answer 7

a. Glutamate
b. Glutamine
d. Proline

Question 8

Which of the following amino acids have six carbon atoms?

Select one or more:

a. Leucine
b. Isoleucine
c. Histidine
d. Proline
e. Glycine

Answer 8

a. Leucine
b. Isoleucine
c. Histidine

Question 9

Which of the following amino acid side chains are nonpolar?

Select one or more:

a. Valine
b. Leucine
c. Asparagine
d. Lysine

Answer 9

a. Valine
b. Leucine

Question 10

Which of the following amino acid side chains are polar?

a. Glutamine
b. Leucine
c. Asparagine
d. Threonine

Answer 10

a. Glutamine
c. Asparagine
d. Threonine

Question 11

Pair the amino acids with their character!

1. Proline
2. Arginine
3. Glutamate
   a. neutral
   b. acidic
   c. basic

• *Select one:**
  a. 1-a, 2-c, 3-b
  b. 1-a, 2-b, 3-c
  c. 1-b, 2-c, 3-a

d. 1-b, 2-a, 3-c
e. 1-c, 2-a, 3-b

Answer 11

a. 1-a, 2-c, 3-b

Question 12

Pair the amino acids with their character! 1. Glutamine 2. Lysine 3. Aspartate
a. neutral b. acidic c. basic

Select one:
a. 1-a, 2-b, 3-c

b. 1-a, 2-c, 3-b
c. 1-b, 2-c, 3-a
d. 1-b, 2-a, 3-c
e. 1-c, 2-a, 3-b

Answer 12

b. 1-a, 2-c, 3-b

Question 13

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 an acidic amino acid.

Answer 13

a. Acidic amino acids have a net negative charge at neutral pH.
b. The isoelectric point of acidic amino acids is at acidic pH.

Question 14

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.

Answer 14

All answers are correct

Question 15

Select the correct statements!

a. Leucine has two asymmetrical 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.

Answer 15

Glycine has no chiral center.

Question 16

What is the dominant form of Arginine at pH 6.0? (pKa values of Arginine are 2.2, 9.0 and 12.5).

Select one:
a. Two positive and one negative charges

b. One positive and two negative charges
c. One negative and one positive charges
d. One negative charge

Answer 16

Two positive and one negative charges

Question 17

What is the dominant form of Glutamate at pH 7.0? (pKa values of Glutamate are 2.2, 5.6 and 9.2)

Select one:
a. One negative charge

b. One negative and one positive charges
c. One positive and two negative charges
d. One positive charge

Answer 17

a. One negative charge

Question 18

What is the dominant form of Histidine at pH 8.0? (pKa values of Histidine are 1.8, 6.0 and 9.2)

a. One positive and one negative charges
b. Two negative and one positive charges
c. One negative charge
d. One positive charge

Answer 18

One positive and one negative charges

Question 19

What is the dominant form of Glycine at low pH (pH=1)?

a. NH2–CH2–COO-
b. NH3+–CH2–COOH
c. NH3+–CH2–COO-
d. NH2–CH2–COOH
e. NH2–CH3+–COO-

Answer 19

b. NH3+–CH2–COOH

Question 20

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.

Answer 20

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.

Question 21

Lysine at its isoelectric point has….

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.

Answer 21

a. a deprotonated a-carboxyl group, a deprotonated–a-amino group and a protonated e-amino group.

Question 22

Lysine at low pH (pH=1) have….

a. no charge at the a-carboxyl group, and two positive charges at the a-and e-amino groups.
b. a negative charge on the a-carboxyl group, a positive charge on the a- amino group and no charge on the e-amino group.
c. a negative charge on the a-carboxyl group, and two positive charges at the a-and e-amino groups.
d. no charge at the a-carboxyl group, a positive charge on the a-amino group and no charge on the e-amino group.
e. no charge at the a-carboxyl group, no charge on the a-amino group and a positive charge on the e-amino group.

Answer 22

a. no charge at the a-carboxyl group, and two positive charges at the a-and e-amino groups.

Question 23

Which of the following statements are true for the isoelectric form of amino acids?

Select one or more:
a. All the naturally occurring amino acids have one positive and one negative charges.

b. The a-amino group of all the naturally occurring amino acids has a positive charge.
c. The a-carboxyl group of all the naturally occurring amino acids has a negative charge.

Answer 23

All answers are correct

Question 24

At neutral pH a tetrapeptide of glycylalanylarginylglutamate has…

a. two positive and three negative 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

Answer 24

e. two positive and two negative charges

Question 25

The arginyllysylaspartate tripeptide has

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.

Answer 25

All answers are correct

Question 26

The chirality of an amino acid results from the fact that its a—carbon…

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.

Answer 26

a. is bonded to four different chemical groups.

Question 27

Of the 20 standard amino acids, only ___________ is not optically active. The reason is that its side chain ___________.

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.

Answer 27

b. glycine; is a hydrogen atom.

Question 28

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.

Answer 28

b. Two –CH2–SH groups are oxidized to form a –CH2–S–S–CH2– disulfide bridge between two cysteines

Question 29

In a highly basic solution, pH = 13, the dominant form of glycine is:

a. NH2–CH2–COO-.
b. NH2–CH2–COOH.
c. NH3+–CH2–COOH.
d. NH3+–CH2–COO-.
e. NH2–CH3+–COO-.

Answer 29

a. NH2–CH2–COO-.

Question 30

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.

Question 31

An octapeptide composed of four repeating glycylalanyl units has:

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.

Answer 31

c. a single free amino group on a glycyl residue and a single free carboxyl group on an alanyl residue

Question 32

At the isoelectric pH of a tetrapeptide:

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.

Answer 32

d. the total net charge is zero.

Question 33

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

Answer 33

c. tertiary structure

Question 34

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.

Answer 34

b. separate proteins exclusively on the basis of molecular weight.

Question 35

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.

Answer 35

b. is the enzyme activity (enzyme as ``units’’) in a milligram of protein.

Question 36

The backbone of two amino acid residues in a protein can be described as (where Ca is C-alpha):

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

Answer 36

a. Ca–C–N–Ca–C–N

Question 37

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

Answer 37

c. Ca–C and N–Ca

Question 38

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.

Answer 38

d. occur mainly between electronegative atoms of the backbone.

Question 39

In a 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.

Answer 39

c. are located outside of the helix spiral.

Question 40

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.

Answer 40

e. a Proline residue.

Question 41

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.

Answer 41

e. of steric hindrance between the bulky Thr and/or Leu side chains.

(Amino acids whose R-groups are too large (tryptophan, tyrosine) or too small (glycine)destabilize α-helices. Proline also destabilizes α-helices because of its irregular geometry; its R-group bonds back to the nitrogen of the amide group, which causes steric hindrance.)

Question 42

What is steric hindrance?

Answer 42

Steric hindrance is the slowing of chemical reactions due to steric bulk

Question 43

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.

Answer 43

b. Ala and Gly.

Question 44

A sequence of amino acids in a certain protein is found to be -Ser-Gly-Pro- Gly-. The sequence is most probably part of:

Select one:

a. b turn.
b. parallel b sheet.
c. a helix.
d. a–sheet.
e. antiparallel b sheet.

Answer 44

a. b turn.

Question 45

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.

Answer 45

e. generally near each other in sequence.

Question 46

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

Answer 46

c. Collagen is a protein in which the polypeptides are mainly in the a-helix conformation

(collagen is an elegant structural motif in which three parallel polypeptide strands in a left-handed, polyproline II-type (PPII) helical conformation coil about each other with a one-residue stagger to form a right-handed triple helix => NOT ALPHA-HELIX)

Question 47

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 disulfide bridges to Cysteine. 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

Answer 47

d. shape remodeling and then chemical oxidation

Question 48

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 fibres.

e. Many have regulatory roles.

Answer 48

b. All subunits must be identical.

Question 49

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 than one polypeptide.
e. proteins consist of amino acids linked by peptide bonds.

Answer 49

a. Nonpolar amino acid side chains are mostly located on the surface of the water-soluble proteins.

Question 50

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.

Answer 50

c. In water-soluble proteins, hydrophobic
(nonpolar) amino acid residues are generally buried and not exposed to water.

Question 51

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.

Answer 51

e. one O atom and one amino acid atom.

Question 52

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.

Answer 52

e. hyperbolic.

Question 53

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.

Answer 53

e. very similar tertiary structures, but different primary structures.

Question 54

In haemoglobin, 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.

Answer 54

b. oxygen binding.

Question 55

Which of the following is not correct concerning 2,3-bisphosphoglycerate (BPG)?

Select one:

a. It is normally found associated with the haemoglobin molecules that are extracted from red blood cells.
b. It decreases the affinity of haemoglobin for oxygen.
c. It binds to the heme groups of haemoglobin.
d. It is an allosteric modulator.
e. It binds with lower affinity to foetal haemoglobin than to adult haemoglobin.

Answer 55

c. It binds to the heme groups of haemoglobin.

Question 56

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

Answer 56

a. hydrophobic

Question 57

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.

Answer 57

e. the binding of a molecule to its binding site affects the binding properties of another site on the same protein.

Question 58

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.

Answer 58

c. They lower the activation energy for the conversion of substrate to product.

Question 59

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 favourable equilibrium
e. Lowering the temperature of a reaction will lower the reaction rate.

Answer 59

b. For S P, a catalyst shifts the reaction equilibrium to the right.

Question 60

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.

Answer 60

a. usually display specificity toward a single reactant.

Question 61

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.

Answer 61

c. substrate binding may induce a conformational change in the enzyme, which then brings catalytic groups into proper orientation.

Question 62

The benefit of measuring the initial rate (V) of a reaction, is that at the beginning of a reaction:

Select one:

a. V=Vmax
b. changes in [S] are negligible, so [S] can be assumed as constant.
c. the effects of allosteric modulators become negligible
d. KM is the lowest at zero time, so the affinity to the substrate is maximal.

e. changes in [ES] will not influence the rate.
f. varying [S] has no effect on V.

Answer 62

b. changes in [S] are negligible, so [S] can be assumed as constant.

Question 63

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=1/2 Vmax.
f. At high substrate concentrations the reaction is of zero order

Answer 63

c. At very high [S], the velocity curve becomes a horizontal line that intersects the y-axis at KM.

Question 64

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.

Answer 64

b. solve, graphically, for the rate of an enzymatic reaction at infinite substrate concentration.

Question 65

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:

Choose correct statments

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
d. 1/2 Vmax.
e. take the reciprocal of the y-axis intercept.
f. multiply the reciprocal of the y-axis intercept by -1

Answer 65

a. multiply the reciprocal of the x-axis intercept by -1.
d. 1/2 Vmax.

Question 66

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.

Answer 66

c. the dissociation constant(Kd) for the ES complex.
e. Vmax

Question 67

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.

Answer 67

b. initial velocity of the catalyzed reaction at [S] >> KM.
d. enzyme concentration

Question 68

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.

Answer 68

d. intercept on the l/[S] axis.

Question 69

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.

Answer 69

c. binds reversibly at the active site.

Question 70

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

Answer 70

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.
d. 1/2 Vmax.

Question 71

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.

Answer 71

c. is twice the rate observed when the concentration of substrate is equal to the KM

Question 72

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.

Answer 72

d. a Histidine residue on the enzyme is involved in the reaction.

Question 73

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

Answer 73

a. binds to the enzyme more tightly than the substrate.

Question 74

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

Answer 74

e. resembles the transition- state structure of the normal enzyme-substrate complex

Question 75

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.

Answer 75

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.

Question 76

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.

Answer 76

b. Heterotropic allosteric effectors compete with substrate for binding sites.

Question 77

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.

Answer 77

c. allosteric inhibitor.

Question 78

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

Answer 78

a. Proteolysis of trypsinogen forms trypsin.

Question 79

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.

Answer 79

a. Basic amino acids have a net positive charge at neutral pH.
b. The isoelectric point of basic amino acids is at basic pH.
d. Arginine is a basic amino acid.

Question 80

Which of the following statements are true for the enzyme at the rate-limiting step of a metabolic pathway?

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

Answer 80

a. Concentration of its substrate is higher than its Km value
b. The measured reaction rate is close to its Vmax

Question 81

Which input path of a branched metabolic pathway is more relevant physiologically?

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

Answer 81

The one that has the highest metabolic flux in vivo

Question 82

Which of the following statements is true when the rate-limiting step of a reaction pathway is inhibited?

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

Answer 82

Concentration of the product at the inhibited enzyme drops

Question 83

Which of the following statements is true for a reaction pathway under conditions of steady-state?

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

Answer 83

Concentrations of intermediers are unaltered

Question 84

Which conditions are necessary for two reactions to be enzymatically coupled? (Eact: activation energy)

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.

Answer 84

b. Eact of both reactions is high.
d. ΔG of the two reactions has different signs (one negative and one positive).

Question 85

Which conditions rule out the enzymatic coupling of two reactions? (Eact: activation energy)

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.

Answer 85

a. One of the reactions has low Eact.
d. ΔG of the two reactions has different signs (one negative and one positive).

Question 86

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.

Answer 86

a. Gtp is the absolute value of the ΔG of hydrolysis (when the group is released).
c. Functional groups have a natural tendency to move from the higher toward the lower gtp.
e. ΔG of a group transfer equals the gtp of the group acceptor minus the gtp of the group donor.

Question 87

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.

Answer 87

all correct

Question 88

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).

Answer 88

a. ΔG of a group transfer equals the gtp of the group acceptor plus the gtp of the group donor.
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.

Question 89

Which statement is true?

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.

Answer 89

All correct

Question 90

Which statement is true?
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.

Answer 90

b. Oxidative catabolism is driven by the high redox potential of molecular O2.
c. Nutrient catabolism provides electrons for reductive biosynthesis.
e. Fuel molecules can be oxidized by the removal of H atoms.

Question 91

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.

Answer 91

b. The whole process is catalyzed by an enzyme complex in the mitochondrial matrix.
e. It yields NADH, which can deliver electrons to complex I of the respiratory chain.

Question 92

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.

Answer 92

a. It cannot occur in anaerobic conditions.
c. It is an irreversible reaction and it cannot be undone (i.e. pyruvate cannot be regenerated from the products).
e. It converts a glucoplastic to a ketoplastic molecule.

Question 93

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.

Answer 93

All correct

Question 94

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

Answer 94

a. It is catalyzed by homodimers of pyruvate decarboxylase in the mitochondrial matrix.
e. It is the last step of anaerobic glycolysis and it produces lactate

Question 95

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.

Answer 95

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.

Question 96

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.

Answer 96

a. Citrate cycle cannot function in anaerobic conditions.
c. Substrate level phosphorylation occurs both in glycolysis and in citrate cycle.
e. ADP activates oxidative phosphorylation as a substrate of Fo F1 ATPase.

Question 97

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.

Answer 97

b. Uncouplers of oxidative phosphorylation cause inhibition of oxidative catabolism.
e. FoF1 ATPase is an active transporter, which can pump protons into the matrix.

Question 98

Which statement is false?

Select one or more:
a. Citrate cycle does not use O2, therefore it can function in anaerobic conditions.

b. Uncouplers of oxidative phosphorylation cause activation of oxidative catabolism.
c. Oxidative phosphorylation is uncoupled when the inner mitochondrial membrane is permeable for ions.
d. Respiration can be inhibited by KCN when oxidative phosphorylation is uncoupled.
e. Respiration can be inhibited by oligomycin when oxidative phosphorylation is uncoupled.

Answer 98

a. Citrate cycle does not use O2, therefore it can function in anaerobic conditions.
e. Respiration can be inhibited by oligomycin when oxidative phosphorylation is uncoupled.

Question 99

Which is prosthetic group in pyruvate-dehydrogenase complex?

Select one or more:

a. flavine mononucleotide (FMN),
b. CoA,
c. thiamine pyrophosphate (TPP),
d. heme,
e. flavine adenine dinucleotide (FAD).

Answer 99

c. thiamine pyrophosphate (TPP),
e. flavine adenine dinucleotide (FAD).

Question 100

Which cofactor is involved in the oxidative decarboxylation of pyruvate?

Select one or more:

a. CoA,
b. flavine mononucleotide (FMN), c. CoQ,
d. NAD+,
e. biotine.

Answer 100

a. CoA,
d. NAD+,

Question 101

Which enzyme contains FAD prosthetic group?

Select one or more:

a. α-ketoglutarate dehydrogenase complex,
b. E3 of PDH complex,
c. mitochondrial glycerol 3-phosphate dehydrogenase,

d. succinate dehydrogenase,
e. malate dehydrogenase.

Answer 101

a. α-ketoglutarate dehydrogenase complex,

b. E3 of PDH complex,
c. mitochondrial glycerol 3-phosphate dehydrogenase,

d. succinate dehydrogenase,

Question 102

Which enzyme contains FAD prosthetic group? Select one or more:

a. Complex I of the respiratory chain,
b. α -ketoglutarate dehydrogenase,

c. malate dehydrogenase,
d. pyruvate dehydrogenase complex,

e. isocitrate dehydrogenase.

Answer 102

b. α -ketoglutarate dehydrogenase,
d. pyruvate dehydrogenase complex,

Question 103

Which enzyme uses NAD+/NADH?

Select one or more:

a. Complex I of the respiratory chain,
b. succinate dehydrogenase,
c. malate dehydrogenase,
d. acyl-CoA dehydrogenase,
e. glyceraldehyde 3-phosphate dehydrogenase

Answer 103

a. Complex I of the respiratory chain,
c. malate dehydrogenase,
e. glyceraldehyde 3-phosphate dehydrogenase.

Question 104

Which activates pyruvate dehydrogenase complex?

Select one or more: a. acetyl-CoA,

b. ATP,
c. ADP,

d. pyruvate dehydrogenase kinase,
e. Ca2+.

Answer 104

c. ADP,
e. Ca2+.

Question 105

Which inhibits pyruvate dehydrogenase complex?

Select one or more:

a. CoA,
b. insulin,
c. ADP,

d. pyruvate dehydrogenase kinase,
e. NADH.

Answer 105

pyruvate dehydrogenase kinase,

NADH.

Question 106

What is the right order of intermediates in citrate cycle?

Select one or more:

a. succinyl-CoA,
b. fumarate,
c. succinate,

d. aalpha-ketoglutarate
e. malate.

Answer 106

d. á-ketoglutarate

a. succinyl-CoA,
c. succinate,

b. fumarate,
e. malate.

Question 107

What is the right order of electron carriers in the respiratory chain?

Select one or more:

a. cytochrome c,
b. succinate,
c. CuB,

d. ubiquinone,
e. FAD.

Answer 107

All correct

Question 108

Put these molecules in the decreasing order of phosphoryl group transfer potential.

Select one or more:

a. ATP,
b. 1-3-bisphosphoglycerate (phosphate on carbon

c. glucose 6-phosphate,
d. phosphoenolpyruvate,
e. phosphocreatine.

Question 109

Which reactions can be enzymatically coupled to each other? (Eact: activation energy)

Select one:

a. one having high Eact and negative ΔG and one having high Eact and positive ΔG.
b. one having low Eact and negative ΔG and one having low Eact and positive ΔG.
c. one having high Eact and negative ΔG and one having low Eact and positive ΔG.
d. two reactions having low Eact and negative ΔG.
e. two reactions having high Eact and positive ΔG

Answer 109

one having high Eact and negative ΔG and one having high Eact and positive ΔG.

Question 110

Which is not involved in oxidative decarboxylation of pyruvate by PDH complex?

Select one:

a. lipoamide,

b. biotin,
c. FAD,
d. CoA,
e. NAD+

Answer 110

b. biotin,

Question 111

Which is not involved in oxidative decarboxylation of pyruvate by PDH complex?

Select one:
a. thiamine pyrophosphate,

b. FAD,
c. NAD+,
d. ubiquinone,
e. CoA.

Answer 111

d. ubiquinone,

Question 112

Chose the correct/right sentence (PDH: pyruvate dehydrogenase complex).
Select one:
a. Pyruvate activates PDH kinase and hence inhibits PDH.

b. Insulin activates PDH kinase and hence activates PDH.
c. ADP inhibits PDH kinase and hence activates PDH.
d. Ca2+ activates PDH phosphatase and hence inhibits PDH.
e. NADH activates PDH phosphatase and hence activates PDH.

Answer 112

c. ADP inhibits PDH kinase and hence activates PDH.

Question 113

Chose the wrong/false sentence:

Select one:
a. Ca2+ activates PDH phosphatase and hence activates PDH.

b. NADH activates PDH phosphatase and hence activates PDH.

c. ADP inhibits PDH kinase and hence activates PDH.
d. Pyruvate inhibits PDH kinase and hence activates PDH.
e. Insulin activates PDH phosphatase and hence activates PDH.

Answer 113

b. NADH activates PDH phosphatase and hence activates PDH.

Question 114

Which enzyme contains FMN prosthetic group?

Select one:
a. E3 enzyme of PDH complex

b. Succinate dehydrogenase
c. Cytochrome c
d. Hexokinase
e. Complex I of respiratory chain

Answer 114

e. Complex I of respiratory chain

Question 115

Which compound can deliver electrons to the respiratory chain directly?

Select one:
a. Fatty acyl-CoA

b. Fumarate
c. Succinyl-CoA

d. Pyruvate
e. Oxaloacetate

Answer 115

a. Fatty acyl-CoA

Question 116

Which compound cannot deliver electrons to the respiratory chain directly?

Select one:
a. Glycerol 3-phosphate

b. NADH
c. Acetyl-CoA
d. Fatty acyl-CoA
e. Succinate

Answer 116

c. Acetyl-CoA

Question 117

Which component of the oxidative phosphorylation is localized in the inter-membrane space?

Select one:

a. Cytochrome a3
b. Ubiquinone (CoQ)
c. Fo subunit of ATP synthase

d. Cytochrome c
e. F1 subunit of ATP synthase

Answer 117

Cytochrome c

Question 118

Identify the nucleotide built from the below ‘X’ isoalloxazine ring.

Answer 118

FAD

Question 119

Identify the missing ‘X’ factor.

Answer 119

H+ + e-

Question 120

Identify molecule ‘X’.

Answer 120

Semiquinone

Question 121

Identify the nucleotide built from the below ‘X’ isoalloxazine ring.

Answer 121

FAD

Question 122

Identify the nucleotide built from the below ‘X’ isoalloxazine.

Answer 122

FADH2

Question 123

Identify Enzyme A

Answer 123

Citrate synthase

Question 124

Identify Enzyme B

Answer 124

Aconitase

Question 125

Identify Enzyme C

Answer 125

Aconitase

Question 126

Identify Enzyme D

Answer 126

Aconitase

Question 127

Identify Enzyme E

Answer 127

Aconitase

Question 128

Identify Enzyme G

Answer 128

Aconitase

Question 129

Identify Enzyme H

Answer 129

Aconitase

Question 130

Identify Enzyme I

Answer 130

Aconitase

Question 131

Identify Enzyme J

Answer 131

Aconitase

Question 132

Identify Cofactor C

Answer 132

NAD+/NADH+H+