MCAT Biology : Glycolysis

Study concepts, example questions & explanations for MCAT Biology

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Example Questions

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Example Question #11 : Glycolysis

Which of the following does not occur in the mitochondrion?

Possible Answers:

Krebs Cycle

Citric acid cycle

Glycolysis

Pyruvate dehydrogenase complex

Oxidative phosphorylation

Correct answer:

Glycolysis

Explanation:

Glycolysis is the only metabolic process of the choices listed that does not occur in the mitochondrion; it occurs in the cytoplasm. Citric acid cycle and Krebs cycle refer to the same process, which occurs in the mitochondrion.

Example Question #11 : Biochemistry And Metabolism

For eukaryotes, the total yield of ATP from NADH is not always maximized when the NADH is manufactured by which of the following?

Possible Answers:

Citric acid cycle

Pyruvate dehydrogenase complex

Electron transport and oxidative phosphorylation

Fermentation

Glycolysis

Correct answer:

Glycolysis

Explanation:

For the NADH produced during glycolysis to be used in the electron transport chain (ETC), the electrons have to be sent into the inner membrane of the mitochondria from the cytoplasm, since glycolysis takes place in the cytoplasm. When the NADH is sent inside, sometimes it skips over NADH dehydrogenase and goes directly to coenzyme Q. The NADH does not always skip over NADH dehydrogenase, but it depends on the shuttle it takes into the mitochondrial matrix. The two shuttles are malate-aspartate, which maximizes NADH's ATP production, and glycerol-3-phosphate, which oxidizes one molecule of NADH, resulting in a decrease in the number of protons pumped. The type of shuttle depends on the cell type. This results in fewer protons being pumped out of the mitochondrial matrix, and thus fewer ATP being formed.

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