bch 3025 exam 3 with complete solutions 2024_2025.

bch 3025 exam 3 with complete solutions
2024/2025




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. - 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. - 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. -
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 -1.72 kJ/mol.
C) G'° is zero.
D) deltaG'° is +1.72 kJ/mol.
E) G'° is incalculably large and positive. - ANSWER✓✓-D) deltaG'° is
+1.72 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. -
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. - 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 - 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) cannot occur because of its large activation energy.
E) may occur in cells at some concentrations of substrate and
product - ANSWER✓✓-E) may occur in cells at some 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. - 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. - ANSWER✓✓-C) -5.4 kJ/mol.

The standard free-energy changes for the reactions below are given.
Phosphocreatine -> creatine + Pi
delta G'° = -43.0 kJ/mol
ATP -> ADP + Pi
delta G'° = -30.5 kJ/mol
What is the overallG'° for the following reaction?
Phosphocreatine + ADP -> creatine + ATP

A) -73.5 kJ/mol
B) -12.5 kJ/mol
C) +12.5 kJ/mol
D) +73.5 kJ/mol
E) G'° cannot be calculated without Keq'. - ANSWER✓✓-B) -12.5
kJ/mol

TheG'° values for the two reactions shown below are given.

Oxaloacetate + acetyl-CoA + H2O -> citrate + CoASH delta G'° = -32.2 kJ/mol
citrate
synthase

Oxaloacetate + acetate -> citrate
delta G'° = -1.9 kJ/mol
citrate lyase