MCB 450 EXAM 3 2026 EXAM WITH
VERIFIED A+ ANSWERS
1. When comparing Glucose to a fatty acid, why does the fatty acid yield more
energy per carbon? - ANSWER Fatty acid carbons are saturated
2. Why is a thioester bond less stable than an ester bond? - ANSWER
Thioester bonds cannot resonate to contain a C=S double bond
3. NADH is a hydride carrier. Upon its oxidation, NADH will _ - ANSWER
Lose 2 electrons and 1 proton
4. The highest energy phosphate bond(s) in ATP is located between which of
the following groups? - ANSWER Two phosphate groups
5. How can the inhibition of phosphofructokinase (PFK1) by ATP lead to the
inhibition of hexokinase? - ANSWER Inhibition of PFK1 results in more
Fructose 6-phosphate, which isomerizes with Glucose 6-phosphate.
Hexokinase is inhibited by elevated Glucose 6-phosphate
6. What happens to phosphofructokinase (PFK1) activity in the presence of
Fructose 2,6 bisphosphate (F2,6BP)? - ANSWER F2,6BP decreases the
inhibitory effects of ATP on PFK1
7. Which of the following statements about integral membrane proteins is
false? - ANSWER They can be released from membranes by treatments that
break hydrogen bonds or interfere withelectorstatic interactions
8. The ultimate product of complete oxidation of methane is _ - ANSWER
CO2
9. A baby who is being weaned from breast milk presents with vomiting,
convulsions, irritability, and jaundice. A biopsy demonstrates that the baby's
liver is severely deficient in Aldolase B activity. Which of the following
substances must be excluded from this patient's diet? - ANSWER Fructose
1
,10.Which of the following statements about membrane transport is not true? -
ANSWER Solutes that cross a cell membrane by facilitated or passive
diffusion will move across the bilayer until the concentration gradient is
reversed.
11.Which of the following mechanisms best explains the effect of insulin
signaling pathway on glucose transport in this treatment? - ANSWER It
move more GLUT-4 transporter to the plasma membrane and increases
glucose uptake
12.The graph below shows the formation of product versus time in the presence
of an enzyme. Why does the amount of product level off as time increases? -
ANSWER The reaction has reached equilibrium; that is, the forward and
reverse reactions are occurring at a fixed rate.
13.The overall reactions for an enzyme-catalyzed conversion can be written as
E + S <-k(-1)--k(1)-> ES --k(2)-> E + P
14.Using this reaction scheme, the rate of breakdown of the enzyme-substrate
complex can be described by the expression: - ANSWER k(-1)[ES] +
k2[ES]
15.What role does fructose 6-phosphate play in the regulation of glucokinase in
the liver? - ANSWER It stimulates the binding of glucokinase to GKRP
16.In the pentose phosphate pathway, what normally inhibits Glucose 6-
phosphate dehydrogenase. - ANSWER Elevated NADPH
17.For a one-substrate, enzyme-catalyzed reaction, double-reciprocal plots were
determined for three different enzyme concentrations. Line one represents
the lowest enzyme concentration, whereas line three represents the highest
enzyme concentration. Which of the following three families of curve would
you expect to be obtained? - ANSWER coming from same starting point,
three line spread out in the order of 1,2,3 from left to right
18.The graph below shows the activity of an enzyme-catalyzed reaction as a
function of temperature. Which statement describes the figure best? -
ANSWER The enzyme becomes denatured and loses the three-dimensional
structure critical for activity.
2
,19.In a highly proliferating cell, ribose-5-phosphate is needed for the synthesis
of nucleic acids and the requirement of NADPH in the cell is diminished.
Which of the following describes the status of the pentose phosphate
pathway (PPP) at that time in the cell? - ANSWER Glycolytic intermediates
such as glceraldehydes-3-phophate and fructose-6-phosphate could flow into
the non-oxidative (reversible) phase of the pentose phosphate pathway for
the production of ribose-5-phosphate
20.Which statement best describes the direction a chemical reaction will
follow? - ANSWER A reaction with positive free energy will proceed in a
forward direction if the substrate concentration is raised high enough
21.The scheme below represents a hypothetical metabolic pathway for the
synthesis of compound X starting with compound S, with enzymes E1-E5
carrying out the successive biochemical steps in the pathway, The pathway
is regulated by feedback inhibition. Which enzyme is most likely to be
inhibited and which compound is the likely inhibitor?
22.S --E1-> T --E2-> U --E3-> V --E4-> W--E5-> X - ANSWER E1 by X
23.The enzyme triosephosphate is isomerase catalyzes the conversion of
glyceraldenhyde-3-phosphte (G3P) to dihydroxyacetone phosphate (DHAP),
and the enzyme's Km for G3P is 1.8E-5. When the concentration of G3P is
24 micromolar, the rate of the reaction, V0, is 72.0 micromoles sec-1. Which
of values A-E is closest to triosephosphate isomerase's Vmax with G3P? -
ANSWER 126 micromoles sec-1
24.Alpha-mannosidase follows Michaelis-Menten kinetics. A 3 micromolar
solution of alpha-mannosidase catalyzes the formation of 0.96 mmoles
paranitrophenol s-1 when incubated with the substrate 4-nitrophenyl alpha-
D-mannoside at a concentration 130 times greater than the Km for that
substrate. What is alpha-mannosidase's kcat? - ANSWER 320 s-1
25.The enzyme beta-fructofuranosidase follows Michaelis-Menten kinetics. A 6
micromolar solution of beta0fructofuranosidase has a kcat of 2167 s-1 when
hydrolyzing sucrose to fructose and glucose. What is beta-
fructofuranosidase's Vmax with sucrose? - ANSWER 13 mmoles s-1
26.Different types of reversible inhibitors of an enzyme that follows Michaelis-
Menten kinetics to give rise to double reciprocal plots A, B, C, and D.
3
, Which double reciprocal plot shows competitive inhibition? - ANSWER
Plot D
27.During the dehydration of 2-phosphoglycerate the enolase reaction in
glycolysis results in: - ANSWER Formation of a C=C double bond after
dehydration to form phosphoenolpyruvate
28.Methanol (CH3OH) is converted by alcohol dehydrogenases to
formaldehyde (CH2O), a compound that is highly toxic to humans. Patients
who have ingested toxic levels of methanol are sometimes treated with
ethanol (CH3CH2OH) to inhibit methanol oxidation by alcohol
dehydrogenase (ADH). Which of the following statements provides the best
rationale for this statement? - ANSWER Ethanol is a structural analog of
methanol that can be expected to compete with methanol for its binding site
on the enzyme.
29.An allosteric enzyme has the following kinetic properties: a Vmax of 25
U/mg enzyme, and a Km,app of 1.0 mM. These kinetic parameters were
then measured in the presence of an allosteric activator. Which one of the
following would best describe the findings of the experiment? - ANSWER A
Vmax of 25 U/mg enzyme, and a Km,app of 0.2 mM.
30.Which is the incorrect statement about the regulation of glycogen synthesis
and degredation? - ANSWER Protein phosphate 1 can activate glycogen
phosphorylase by removing phosphate groups
31.Glucose-6-phosphate dehydrogenase (G6PD) deficiency in mature
erythrocytes can lead to hemolytic anemia. The reason for cellular lysis of
erythrocytes in this situation is due to the - ANSWER decreased levels of
NADPH leading to low levels of reduced glutathione as an antioxidant to
protect red cells from oxidative damage.
32.Which of these is an effect of epinephrine secretion in response to low blood
glucose levels? - ANSWER increased glycogen breakdown in muscle
33.A healthy adult is taking a glucose tolerance test. After ingestion of 75 gm of
glucose, the serum glucose concentration increases to 20 mg/dL in 30
minutes. It decreases to 100 mg/dL in two hours. Which of the following
enzymes is responsible for the rapid capture of glucose by the liver under
4
VERIFIED A+ ANSWERS
1. When comparing Glucose to a fatty acid, why does the fatty acid yield more
energy per carbon? - ANSWER Fatty acid carbons are saturated
2. Why is a thioester bond less stable than an ester bond? - ANSWER
Thioester bonds cannot resonate to contain a C=S double bond
3. NADH is a hydride carrier. Upon its oxidation, NADH will _ - ANSWER
Lose 2 electrons and 1 proton
4. The highest energy phosphate bond(s) in ATP is located between which of
the following groups? - ANSWER Two phosphate groups
5. How can the inhibition of phosphofructokinase (PFK1) by ATP lead to the
inhibition of hexokinase? - ANSWER Inhibition of PFK1 results in more
Fructose 6-phosphate, which isomerizes with Glucose 6-phosphate.
Hexokinase is inhibited by elevated Glucose 6-phosphate
6. What happens to phosphofructokinase (PFK1) activity in the presence of
Fructose 2,6 bisphosphate (F2,6BP)? - ANSWER F2,6BP decreases the
inhibitory effects of ATP on PFK1
7. Which of the following statements about integral membrane proteins is
false? - ANSWER They can be released from membranes by treatments that
break hydrogen bonds or interfere withelectorstatic interactions
8. The ultimate product of complete oxidation of methane is _ - ANSWER
CO2
9. A baby who is being weaned from breast milk presents with vomiting,
convulsions, irritability, and jaundice. A biopsy demonstrates that the baby's
liver is severely deficient in Aldolase B activity. Which of the following
substances must be excluded from this patient's diet? - ANSWER Fructose
1
,10.Which of the following statements about membrane transport is not true? -
ANSWER Solutes that cross a cell membrane by facilitated or passive
diffusion will move across the bilayer until the concentration gradient is
reversed.
11.Which of the following mechanisms best explains the effect of insulin
signaling pathway on glucose transport in this treatment? - ANSWER It
move more GLUT-4 transporter to the plasma membrane and increases
glucose uptake
12.The graph below shows the formation of product versus time in the presence
of an enzyme. Why does the amount of product level off as time increases? -
ANSWER The reaction has reached equilibrium; that is, the forward and
reverse reactions are occurring at a fixed rate.
13.The overall reactions for an enzyme-catalyzed conversion can be written as
E + S <-k(-1)--k(1)-> ES --k(2)-> E + P
14.Using this reaction scheme, the rate of breakdown of the enzyme-substrate
complex can be described by the expression: - ANSWER k(-1)[ES] +
k2[ES]
15.What role does fructose 6-phosphate play in the regulation of glucokinase in
the liver? - ANSWER It stimulates the binding of glucokinase to GKRP
16.In the pentose phosphate pathway, what normally inhibits Glucose 6-
phosphate dehydrogenase. - ANSWER Elevated NADPH
17.For a one-substrate, enzyme-catalyzed reaction, double-reciprocal plots were
determined for three different enzyme concentrations. Line one represents
the lowest enzyme concentration, whereas line three represents the highest
enzyme concentration. Which of the following three families of curve would
you expect to be obtained? - ANSWER coming from same starting point,
three line spread out in the order of 1,2,3 from left to right
18.The graph below shows the activity of an enzyme-catalyzed reaction as a
function of temperature. Which statement describes the figure best? -
ANSWER The enzyme becomes denatured and loses the three-dimensional
structure critical for activity.
2
,19.In a highly proliferating cell, ribose-5-phosphate is needed for the synthesis
of nucleic acids and the requirement of NADPH in the cell is diminished.
Which of the following describes the status of the pentose phosphate
pathway (PPP) at that time in the cell? - ANSWER Glycolytic intermediates
such as glceraldehydes-3-phophate and fructose-6-phosphate could flow into
the non-oxidative (reversible) phase of the pentose phosphate pathway for
the production of ribose-5-phosphate
20.Which statement best describes the direction a chemical reaction will
follow? - ANSWER A reaction with positive free energy will proceed in a
forward direction if the substrate concentration is raised high enough
21.The scheme below represents a hypothetical metabolic pathway for the
synthesis of compound X starting with compound S, with enzymes E1-E5
carrying out the successive biochemical steps in the pathway, The pathway
is regulated by feedback inhibition. Which enzyme is most likely to be
inhibited and which compound is the likely inhibitor?
22.S --E1-> T --E2-> U --E3-> V --E4-> W--E5-> X - ANSWER E1 by X
23.The enzyme triosephosphate is isomerase catalyzes the conversion of
glyceraldenhyde-3-phosphte (G3P) to dihydroxyacetone phosphate (DHAP),
and the enzyme's Km for G3P is 1.8E-5. When the concentration of G3P is
24 micromolar, the rate of the reaction, V0, is 72.0 micromoles sec-1. Which
of values A-E is closest to triosephosphate isomerase's Vmax with G3P? -
ANSWER 126 micromoles sec-1
24.Alpha-mannosidase follows Michaelis-Menten kinetics. A 3 micromolar
solution of alpha-mannosidase catalyzes the formation of 0.96 mmoles
paranitrophenol s-1 when incubated with the substrate 4-nitrophenyl alpha-
D-mannoside at a concentration 130 times greater than the Km for that
substrate. What is alpha-mannosidase's kcat? - ANSWER 320 s-1
25.The enzyme beta-fructofuranosidase follows Michaelis-Menten kinetics. A 6
micromolar solution of beta0fructofuranosidase has a kcat of 2167 s-1 when
hydrolyzing sucrose to fructose and glucose. What is beta-
fructofuranosidase's Vmax with sucrose? - ANSWER 13 mmoles s-1
26.Different types of reversible inhibitors of an enzyme that follows Michaelis-
Menten kinetics to give rise to double reciprocal plots A, B, C, and D.
3
, Which double reciprocal plot shows competitive inhibition? - ANSWER
Plot D
27.During the dehydration of 2-phosphoglycerate the enolase reaction in
glycolysis results in: - ANSWER Formation of a C=C double bond after
dehydration to form phosphoenolpyruvate
28.Methanol (CH3OH) is converted by alcohol dehydrogenases to
formaldehyde (CH2O), a compound that is highly toxic to humans. Patients
who have ingested toxic levels of methanol are sometimes treated with
ethanol (CH3CH2OH) to inhibit methanol oxidation by alcohol
dehydrogenase (ADH). Which of the following statements provides the best
rationale for this statement? - ANSWER Ethanol is a structural analog of
methanol that can be expected to compete with methanol for its binding site
on the enzyme.
29.An allosteric enzyme has the following kinetic properties: a Vmax of 25
U/mg enzyme, and a Km,app of 1.0 mM. These kinetic parameters were
then measured in the presence of an allosteric activator. Which one of the
following would best describe the findings of the experiment? - ANSWER A
Vmax of 25 U/mg enzyme, and a Km,app of 0.2 mM.
30.Which is the incorrect statement about the regulation of glycogen synthesis
and degredation? - ANSWER Protein phosphate 1 can activate glycogen
phosphorylase by removing phosphate groups
31.Glucose-6-phosphate dehydrogenase (G6PD) deficiency in mature
erythrocytes can lead to hemolytic anemia. The reason for cellular lysis of
erythrocytes in this situation is due to the - ANSWER decreased levels of
NADPH leading to low levels of reduced glutathione as an antioxidant to
protect red cells from oxidative damage.
32.Which of these is an effect of epinephrine secretion in response to low blood
glucose levels? - ANSWER increased glycogen breakdown in muscle
33.A healthy adult is taking a glucose tolerance test. After ingestion of 75 gm of
glucose, the serum glucose concentration increases to 20 mg/dL in 30
minutes. It decreases to 100 mg/dL in two hours. Which of the following
enzymes is responsible for the rapid capture of glucose by the liver under
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