Question 1

Where does the TCA cycle occur?

Accepted Answer

The TCA cycle occurs in the mitochondrial matrix in eukaryotic cells. Succinate dehydrogenase is the exception among its eight enzymes because it is embedded in the inner mitochondrial membrane.

Question 2

How many carbon dioxide molecules are released per acetyl-CoA?

Accepted Answer

Two molecules of carbon dioxide are released per turn of the TCA cycle. The two decarboxylation steps are isocitrate to alpha-ketoglutarate and alpha-ketoglutarate to succinyl-CoA.

Question 3

What is the energy yield of one TCA turn?

Accepted Answer

One turn per acetyl-CoA yields 3 NADH, 1 FADH2, 1 GTP and 2 carbon dioxide. The single GTP is treated as one ATP equivalent.

Question 4

Why is the TCA cycle called an amphibolic pathway?

Accepted Answer

It is called amphibolic because it participates in both breakdown and biosynthesis. Intermediates such as citrate, alpha-ketoglutarate, succinyl-CoA and oxaloacetate can leave the cycle and support synthesis of fatty acids, amino acids, haem and glucose-related compounds.

Question 5

What is the TCA-cycle yield from one glucose molecule?

Accepted Answer

Two acetyl-CoA molecules produce two turns of the TCA cycle. The cycle therefore yields 6 NADH, 2 FADH2, 2 GTP and 4 carbon dioxide per glucose, excluding glycolysis and the electron transport chain.

TCA Cycle & Amphibolic Pathways — 3D Mitochondrial Furnace

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