Question 1

Which enzyme catalyzes the conversion of glucose-6-phosphate to fructose-6-phosphate in glycolysis?

Accepted Answer

Phosphoglucose isomerase

Question 2

Given the reaction: $$	ext{Glucose} + 	ext{ATP} ightarrow 	ext{Glucose-6-phosphate} + 	ext{ADP} + 	ext{H}^+$$, which of the following best describes the role of ATP?

Accepted Answer

ATP provides the phosphate group and energy for phosphorylation

Question 3

The standard free energy change ($$\Delta G^\circ') $$for the reaction catalyzed by phosphofructokinase is $$-14.2 kJ/$$mol. What does this indicate about the reaction under standard conditions?

Accepted Answer

The reaction is exergonic and will proceed spontaneously

Question 4

Which of the following best explains why phosphofructokinase is inhibited by high concentrations of ATP?

Accepted Answer

High ATP signals that the cell has sufficient energy, so glycolysis is slowed to prevent excess ATP production

Question 5

If the equilibrium constant ($$K_{eq}) $$for the reaction $$	ext{Glucose-6-phosphate} ightleftharpoons 	ext{Fructose-6-phosphate} at 298 K is 0.5$$, what is the value of $$\Delta G^\circ'$$ for this reaction? (Use $$\Delta G^\circ' = -RT \ln K_{eq}$$, $$R = 8.314 J/$$mol·K)

Accepted Answer

$$\Delta G^\circ' = 1.72 kJ/$$mol

Question 6

A patient’s erythrocytes are found to have a steady-state concentration of ATP at 2.5 mM and glucose-6-phosphate at 0.1 mM. If the standard free energy change for ATP hydrolysis is $$-30.5 kJ/$$mol, what is the actual free energy change ($$\Delta G) $$for ATP hydrolysis in these cells? (Use $$\Delta G = \Delta G^\circ' + RT \ln \frac{[ADP][P_i]}{[ATP]}$$ and assume $$[ADP][P_i] = 0.01 mM)$$

Accepted Answer

$$\Delta G is $$more negative than $$\Delta G^\circ'$$

Question 7

Which of the following reactions in glycolysis is most likely to be irreversible under cellular conditions?

Accepted Answer

Fructose-6-phosphate $$\rightarrow$$ Fructose-1,6-bisphosphate

Question 8

During the aldolase reaction, fructose-1,6-bisphosphate is cleaved into two three-carbon molecules. Which of the following best describes the products?

Accepted Answer

Dihydroxyacetone phosphate and glyceraldehyde-3-phosphate

Question 9

If 100 molecules of glucose undergo glycolysis through the first 7 reactions (up to phosphoglycerate kinase), and no branching occurs, how many molecules of 1,3-bisphosphoglycerate are produced at equilibrium?

Accepted Answer

200 molecules

Question 10

Which enzyme catalyzes the interconversion between dihydroxyacetone phosphate and glyceraldehyde-3-phosphate?

Accepted Answer

Triose phosphate isomerase

Question 11

In glycolysis, which step is coupled to ATP hydrolysis to drive an otherwise unfavorable reaction?

Accepted Answer

Glucose $$\rightarrow$$ Glucose-6-phosphate

Question 12

Which of the following best describes the oxidation state change of the carbon atom in glyceraldehyde-3-phosphate during its conversion to 1,3-bisphosphoglycerate?

Accepted Answer

The carbon is oxidized

Question 13

If the steady-state concentration of fructose-1,6-bisphosphate in erythrocytes is $$0.001 mM $$and that of dihydroxyacetone phosphate is $$0.06 mM$$, what does this suggest about the equilibrium of the aldolase reaction?

Accepted Answer

The reaction favors the formation of dihydroxyacetone phosphate and glyceraldehyde-3-phosphate

Question 14

Which of the following is the correct formula to calculate the equilibrium constant ($$K_{eq}) $$from the standard free energy change ($$\Delta G^\circ'$$)?

Accepted Answer

$$K_{eq} = e$$^{-\frac{\Delta G^\circ'}$${RT}}$$

Question 15

Which glycolytic intermediate is the substrate for the enzyme phosphoglycerate kinase?

Accepted Answer

1,3-bisphosphoglycerate

Question 16

A mutation in phosphoglucose isomerase prevents the conversion of glucose-6-phosphate to fructose-6-phosphate. What is the most likely consequence for glycolysis?

Accepted Answer

Glycolysis will be blocked after the first step

Question 17

Which of the following best explains why the conversion of phosphoenolpyruvate to pyruvate is highly exergonic?

Accepted Answer

The tautomerization of enolpyruvate to keto pyruvate releases energy

Question 18

If the enzyme concentration is increased for the reaction $$	ext{Glucose-6-phosphate} ightleftharpoons 	ext{Fructose-6-phosphate}$$, what effect does this have on the equilibrium concentrations of reactants and products?

Accepted Answer

Equilibrium concentrations remain unchanged; only the rate increases

Glycolysis: Thermodynamics, Enzyme Mechanisms, and Regulation

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