BCH3025 Exam 3 UPDATED Exam
Questions and CORRECT Answers
If the G'° of the reaction A -> B is -40 kJ/mol, under standard conditions the reaction:
A) is at equilibrium.
B) will never reach equilibrium.
C) will not occur spontaneously.
D) will proceed at a rapid rate.
E) will proceed spontaneously from left to right. - CORRECT ANSWER - E) will proceed
spontaneously from left to right.
For the reaction A - B,G'° = -60 kJ/mol. The reaction is started with 10 mmol of A; no B is
initially present. After 24 hours, analysis reveals the presence of 2 mmol of B, 8 mmol of A.
Which is the most likely explanation?
A) A and B have reached equilibrium concentrations.
B) An enzyme has shifted the equilibrium toward A.
C) B formation is kinetically slow; equilibrium has not been reached by 24 hours.
D) Formation of B is thermodynamically unfavorable.
E) The result described is impossible, given the fact thatG'° is -60 kJ/mol. - CORRECT
ANSWER - C) B formation is kinetically slow; equilibrium has not been reached by 24
hours.
When a mixture of 3-phosphoglycerate and 2-phosphoglycerate is incubated at 25°C with
phosphoglycerate mutase until equilibrium is reached, the final mixture contains six times as
much 2-phosphoglycerate as 3-phosphoglycerate. Which one of the following statements is most
nearly correct, when applied to the reaction as written? (R = 8.315 J/mol·K; T = 298 K)
3-Phosphoglycerate 2-phosphoglycerate
A) delta G'° is -4.44 kJ/mol.
,B) G'° is zero.
C) G'° is +12.7 kJ/mol.
D) G'° is incalculably large and positive.
E) G'° cannot be calculated from the information given. - CORRECT ANSWER - A) delta
G'° is -4.44 kJ/mol.
When a mixture of glucose 6-phosphate and fructose 6-phosphate is incubated with the enzyme
phosphohexose isomerase (which catalyzes the interconversion of these two compounds) until
equilibrium is reached, the final mixture contains twice as much glucose 6-phosphate as fructose
6-phosphate. Which one of the following statements is best applied to this reaction outlined
below?
(R = 8.315 J/mol·K; T = 298 K)
Glucose 6-phosphate fructose 6-phosphate
A) G'° is incalculably large and negative.
B) G'° is -1.7 kJ/mol.
C) G'° is zero.
D) deltaG'° is +1.7 kJ/mol.
E) G'° is incalculably large and positive. - CORRECT ANSWER - D) deltaG'° is +1.7
kJ/mol.
Hydrolysis of 1 M glucose 6-phosphate catalyzed by glucose 6-phosphatase is 99% complete at
equilibrium (in other words, only 1% of the substrate remains). Which of the following
statements is most nearly correct? (R = 8.315 J/mol·K; T = 298 K)
A) deltaG'° = -11 kJ/mol.
B) G'° = -5 kJ/mol.
C) G'° = 0 kJ/mol.
D) G'° = +11 kJ/mol.
E) G'° cannot be determined from the information given. - CORRECT ANSWER - A)
deltaG'° = -11 kJ/mol.
,The reaction A + B C has aG'° of -20 kJ/mol at 25°C. Starting under standard conditions, one can
predict that:
A) at equilibrium, the concentration of B will exceed the concentration of A.
B) at equilibrium, the concentration of C will be less than the concentration of A.
C) at equilibrium, the concentration of C will be much greater than the concentration of A or B.
D) C will rapidly break down to A + B.
E) when A and B are mixed, the reaction will proceed rapidly toward formation of C. -
CORRECT ANSWER - C) at equilibrium, the concentration of C will be much greater
than the concentration of A or B.
Which of the following compounds has the largest negative value for the standard free-energy
change (deltaG'°) upon hydrolysis?
A) Acetic anhydride
B) Glucose 6-phosphate
C) Glutamine
D) Glycerol 3-phosphate
E) Lactose - CORRECT ANSWER - A) Acetic anhydride
For the following reaction, deltaG'° = +29.7 kJ/mol.
L-Malate + NAD+ oxaloacetate + NADH + H+
The reaction as written:
A) can never occur in a cell.
B) can occur in a cell only if it is coupled to another reaction for whichG'° is positive.
C) can occur only in a cell in which NADH is converted to NAD+ by electron transport.
D) may occur in cells at certain concentrations of substrate and product.
, E) would always proceed at a very slow rate - CORRECT ANSWER - D) may occur in
cells at certain concentrations of substrate and product.
For the reaction A -> B, the Keq' is 10^4. If a reaction mixture originally contains 1 mmol of A
and no B, which one of the following must be true?
A) At equilibrium, there will be far more B than A.
B) The rate of the reaction is very slow.
C) The reaction requires coupling to an exergonic reaction in order to proceed.
D) The reaction will proceed toward B at a very high rate.
E) G'° for the reaction will be large and positive. - CORRECT ANSWER - A) At
equilibrium, there will be far more B than A.
During glycolysis, glucose 1-phosphate is converted to fructose 6-phosphate in two successive
reactions:
Glucose 1-phosphate-> glucose 6-phosphate
delta G'° = -7.1 kJ/mol
Glucose 6-phosphate-> fructose 6-phosphate
delta G'° = +1.7 kJ/mol
delta G'° for the overall reaction is:
A) -8.8 kJ/mol.
B) -7.1 kJ/mol.
C) -5.4 kJ/mol.
D) +5.4 kJ/mol.
E) +8.8 kJ/mol. - CORRECT ANSWER - C) -5.4 kJ/mol.
The standard free-energy changes for the reactions below are given.
Questions and CORRECT Answers
If the G'° of the reaction A -> B is -40 kJ/mol, under standard conditions the reaction:
A) is at equilibrium.
B) will never reach equilibrium.
C) will not occur spontaneously.
D) will proceed at a rapid rate.
E) will proceed spontaneously from left to right. - CORRECT ANSWER - E) will proceed
spontaneously from left to right.
For the reaction A - B,G'° = -60 kJ/mol. The reaction is started with 10 mmol of A; no B is
initially present. After 24 hours, analysis reveals the presence of 2 mmol of B, 8 mmol of A.
Which is the most likely explanation?
A) A and B have reached equilibrium concentrations.
B) An enzyme has shifted the equilibrium toward A.
C) B formation is kinetically slow; equilibrium has not been reached by 24 hours.
D) Formation of B is thermodynamically unfavorable.
E) The result described is impossible, given the fact thatG'° is -60 kJ/mol. - CORRECT
ANSWER - C) B formation is kinetically slow; equilibrium has not been reached by 24
hours.
When a mixture of 3-phosphoglycerate and 2-phosphoglycerate is incubated at 25°C with
phosphoglycerate mutase until equilibrium is reached, the final mixture contains six times as
much 2-phosphoglycerate as 3-phosphoglycerate. Which one of the following statements is most
nearly correct, when applied to the reaction as written? (R = 8.315 J/mol·K; T = 298 K)
3-Phosphoglycerate 2-phosphoglycerate
A) delta G'° is -4.44 kJ/mol.
,B) G'° is zero.
C) G'° is +12.7 kJ/mol.
D) G'° is incalculably large and positive.
E) G'° cannot be calculated from the information given. - CORRECT ANSWER - A) delta
G'° is -4.44 kJ/mol.
When a mixture of glucose 6-phosphate and fructose 6-phosphate is incubated with the enzyme
phosphohexose isomerase (which catalyzes the interconversion of these two compounds) until
equilibrium is reached, the final mixture contains twice as much glucose 6-phosphate as fructose
6-phosphate. Which one of the following statements is best applied to this reaction outlined
below?
(R = 8.315 J/mol·K; T = 298 K)
Glucose 6-phosphate fructose 6-phosphate
A) G'° is incalculably large and negative.
B) G'° is -1.7 kJ/mol.
C) G'° is zero.
D) deltaG'° is +1.7 kJ/mol.
E) G'° is incalculably large and positive. - CORRECT ANSWER - D) deltaG'° is +1.7
kJ/mol.
Hydrolysis of 1 M glucose 6-phosphate catalyzed by glucose 6-phosphatase is 99% complete at
equilibrium (in other words, only 1% of the substrate remains). Which of the following
statements is most nearly correct? (R = 8.315 J/mol·K; T = 298 K)
A) deltaG'° = -11 kJ/mol.
B) G'° = -5 kJ/mol.
C) G'° = 0 kJ/mol.
D) G'° = +11 kJ/mol.
E) G'° cannot be determined from the information given. - CORRECT ANSWER - A)
deltaG'° = -11 kJ/mol.
,The reaction A + B C has aG'° of -20 kJ/mol at 25°C. Starting under standard conditions, one can
predict that:
A) at equilibrium, the concentration of B will exceed the concentration of A.
B) at equilibrium, the concentration of C will be less than the concentration of A.
C) at equilibrium, the concentration of C will be much greater than the concentration of A or B.
D) C will rapidly break down to A + B.
E) when A and B are mixed, the reaction will proceed rapidly toward formation of C. -
CORRECT ANSWER - C) at equilibrium, the concentration of C will be much greater
than the concentration of A or B.
Which of the following compounds has the largest negative value for the standard free-energy
change (deltaG'°) upon hydrolysis?
A) Acetic anhydride
B) Glucose 6-phosphate
C) Glutamine
D) Glycerol 3-phosphate
E) Lactose - CORRECT ANSWER - A) Acetic anhydride
For the following reaction, deltaG'° = +29.7 kJ/mol.
L-Malate + NAD+ oxaloacetate + NADH + H+
The reaction as written:
A) can never occur in a cell.
B) can occur in a cell only if it is coupled to another reaction for whichG'° is positive.
C) can occur only in a cell in which NADH is converted to NAD+ by electron transport.
D) may occur in cells at certain concentrations of substrate and product.
, E) would always proceed at a very slow rate - CORRECT ANSWER - D) may occur in
cells at certain concentrations of substrate and product.
For the reaction A -> B, the Keq' is 10^4. If a reaction mixture originally contains 1 mmol of A
and no B, which one of the following must be true?
A) At equilibrium, there will be far more B than A.
B) The rate of the reaction is very slow.
C) The reaction requires coupling to an exergonic reaction in order to proceed.
D) The reaction will proceed toward B at a very high rate.
E) G'° for the reaction will be large and positive. - CORRECT ANSWER - A) At
equilibrium, there will be far more B than A.
During glycolysis, glucose 1-phosphate is converted to fructose 6-phosphate in two successive
reactions:
Glucose 1-phosphate-> glucose 6-phosphate
delta G'° = -7.1 kJ/mol
Glucose 6-phosphate-> fructose 6-phosphate
delta G'° = +1.7 kJ/mol
delta G'° for the overall reaction is:
A) -8.8 kJ/mol.
B) -7.1 kJ/mol.
C) -5.4 kJ/mol.
D) +5.4 kJ/mol.
E) +8.8 kJ/mol. - CORRECT ANSWER - C) -5.4 kJ/mol.
The standard free-energy changes for the reactions below are given.
