Question 1

Describe the fate of pyruvate, formed by glycolysis in animal skeletal muscle, under two conditions: (a) at rest, and (b) during an all-out sprint. Show enough detail in your answer to explain why pyruvate metabolism is different in these two cases.

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Question 2

The yeast used in brewing the alcoholic beverage beer can break down glucose either aerobically or anaerobically using alcoholic fermentation. Explain why beer is brewed under anaerobic conditions.

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Question 3

Explain why the phosphorolysis of glycogen is more efficient than the hydrolysis of glycogen in mobilizing glucose for the glycolytic pathway.

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Question 4

At which point in glycolysis do C-3 and C-4 of glucose become chemically equivalent?

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Question 5

Explain the biochemical basis of the human metabolic disorder called lactose intolerance.

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Question 6

In the conversion of glucose to pyruvate via glycolysis, all of the following enzymes participate. Indicate the order in which they function by numbering them.
___ hexokinase
___ triose phosphate isomerase
___ phosphohexose isomerase
___ enolase
___ glyceraldehyde 3-phosphate dehydrogenase
___ pyruvate kinase
___ phosphofructokinase-1
Which of the enzymes represents a major regulation point in glycolysis?
Which catalyzes a reaction in which ATP is produced?
Which catalyzes a reaction in which NADH is produced?

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Question 7

What are the two reactions in glycolysis in which aldose to ketose isomerization is catalyzed by an enzyme? For both reactions the $\Delta$ G'° is positive. Briefly explain how the reactions are able to proceed without the input of additional energy.

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Question 8

Describe the process of glycogen breakdown in muscle. Include a description of the structure of glycogen, the nature of the breakdown reaction and the breakdown product, and the required enzyme(s).

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Question 9

All of the intermediated in the glycolytic pathway are phosphorylated. Give two plausible reasons why this might be advantageous to the cell.

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Question 10

Yeast can metabolize D-mannose to ethanol and CO₂. In addition to the glycolytic enzymes, the only other enzyme needed is phosphomannose isomerase, which converts mannose 6-phosphate to fructose 6-phosphate. If mannose is converted to ethanol and CO₂ by the most direct pathway, which of the compounds and cofactors in this list are involved? A. Lactate B. Acetaldehyde C. Acetyl-CoA D. FAD E. Glucose 6-phosphate F. Fructose 1-phosphate G. Pyruvate H. Lipoic acid I. Thiamine pyrophosphate J. Dihydroxyacetone phosphate

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Question 11

When glucose is oxidized via glycolysis, the carbon atom that bears the phosphate in the 3-phosphoglycerate formed may have originally been either C-1 or C-6 of the original glucose. Describe this pathway in just enough detail to explain this fact.

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Question 12

The conversion of glyceraldehyde 3-phosphate to dihydroxyacetone phosphate is catalyzed by triose phosphate isomerase. The standard free-energy change ($\Delta$ G'°) for this reaction is -7.5 kJ/mol. Define the equilibrium constant for the reaction and calculate it using only the data given here. (R = 8.315 J/mol · K; T = 298 K)

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Question 13

Describe the glycolytic pathway from glucose to glyceraldehyde 3-phosphate. Show structures of intermediates, enzyme names, and indicate where any cofactors participate.

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Question 14

What would be the products of the reaction, if aldolase used glucose-6-phosphate instead of fructose-1,6-bisphosphate? Based on your answer, can you suggest a possible rationale for why nature chose to include two extra steps prior to the aldolase step?

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Question 15

If brewer's yeast is mixed with pure sugar (glucose) in the absence of phosphate (P_i), no ethanol is produced. With the addition of a little P_i, ethanol production soon begins. Explain this observation in 25 words or less.

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Question 16

The conversion of glucose into glucose 6-phosphate, which must occur in the breakdown of glucose, is thermodynamically unfavorable (endergonic). How do cells overcome this problem?

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Question 17

Describe the glycolytic pathway from glyceraldehyde 3-phosphate to pyruvate, showing structures of intermediates and names of enzymes. Indicate where any cofactors participate.

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Question 18

Two reactions in glycolysis produce ATP. For each of these, show the name and structure of reactant and product, indicate which cofactors participate and where, and name the enzymes.

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Question 19

Explain why P_i (inorganic phosphate) is absolutely required for glycolysis to proceed.

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Question 20

Explain with words, diagrams, or structures why lactate accumulates in the blood during bursts of very vigorous exercise (such as a 100-meter dash).

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Quiz 14: Glycolysis, Gluconeogenesis, and the Pentose Phosphate Pathway