Chapter 13 Application

A researcher blocks the isomerase that converts glucose-6-phosphate to fructose-6-phosphate. Which later glycolysis reactions are affected?

Formation of fructose-1,6-bisphosphate and subsequent downstream glycolysis are reduced because the pathway cannot proceed normally past glucose-6-phosphate.

A drug inhibits glyceraldehyde-3-phosphate dehydrogenase. What happens to NADH formation and downstream ATP production through glycolysis?

NADH production at step 6 decreases, and downstream ATP production declines because the pathway is blocked at an essential oxidation step.

A cell can make pyruvate through glycolysis but cannot convert pyruvate into acetyl-CoA. Which pathway loses a major source of carbon?

The citric acid cycle loses acetyl-CoA derived from glucose, reducing cycle activity and downstream electron-carrier production.

A mutation blocks succinyl-CoA conversion to succinate. Which type of ATP-generating reaction is directly affected?

Substrate-level phosphorylation in the citric acid cycle, which normally produces GTP or ATP during this reaction.

A cell's electron-transport chain stops working, but glycolysis remains functional. Explain why ATP production falls and why lactate may increase.

Oxidative phosphorylation decreases because proton pumping is impaired. Lactate production may increase to regenerate NAD+, allowing glycolysis to continue producing a small amount of ATP.

A cell has high ATP and low ADP. How might this affect the activity of ATP-producing metabolic pathways?

High energy availability can reduce the activity of key regulated enzymes and decrease the flux through ATP-producing pathways.

A cell needs glucose synthesis. Why must it regulate glycolysis and gluconeogenesis so that they do not operate fully in opposite directions at the same time?

Simultaneous operation would waste energy by cycling between glucose breakdown and glucose synthesis without useful net production.

A researcher measures two molecules of pyruvate, two net ATP, and two NADH from one glucose molecule. Which pathway produced these products?

Glycolysis.

A fatty-acid molecule undergoes one cycle of beta-oxidation. What happens to its carbon chain, and what energy-related products are formed?

The fatty-acid chain is shortened by two carbons, producing acetyl-CoA, NADH, and FADH2.

A cell has an adequate supply of NAD+ but very little ATP. Can glycolysis still proceed, and why?

Yes, provided the required substrates and enzymes are available. Glycolysis uses ATP initially but generates a net two ATP per glucose.

A cell cannot regenerate NAD+ and begins accumulating NADH. Why is this a problem for glycolysis?

NAD+ is required for the oxidation of glyceraldehyde-3-phosphate. Without enough NAD+, glycolysis cannot continue at its normal rate.

A mutation reduces the activity of fructose-1,6-bisphosphatase. Which pathway is directly impaired, and why?

Gluconeogenesis is impaired because the enzyme is needed to convert fructose-1,6-bisphosphate to fructose-6-phosphate.

A cell has normal glycolysis but reduced citric acid cycle activity. Predict the effect on NADH and FADH2 production and explain the downstream consequence.

Production of NADH and FADH2 through the cycle decreases, potentially reducing electron delivery to the respiratory chain and ATP synthesis.