ap bio 7.3: After pyruvate is oxidized, the citric acid cycle completes the energy-yielding oxidation of organic molecules

What is the primary role of the citric acid cycle?

To complete the breakdown of glucose by oxidizing Acetyl CoA into CO2 and producing energy-carrying molecules like NADH, FADH2, and ATP.

What must happen before the citric acid cycle can begin?

Pyruvate from glycolysis must be converted into Acetyl CoA in the mitochondria.

What molecule enters the citric acid cycle?

Acetyl CoA combines with oxaloacetate to form citrate.

How many steps are in the citric acid cycle?

Eight steps, each catalyzed by a specific enzyme.

What happens in the first step of the citric acid cycle?

Acetyl CoA combines with oxaloacetate to form citrate, catalyzed by citrate synthase.

What happens to citrate in the second step?

Citrate is converted into isocitrate through a rearrangement involving the loss and gain of a water molecule, catalyzed by aconitase.

What happens to isocitrate in the third step?

Isocitrate is oxidized by NAD+ and loses CO2 to form alpha-ketoglutarate, catalyzed by isocitrate dehydrogenase.

What happens to a-ketoglutarate in the fourth step?

a-ketoglutarate is further oxidized by NAD+, loses CO2, and joins with CoA to form succinyl CoA, catalyzed by ketoglutarate dehydrogenase.

What happens to succinyl CoA in the fifth step?

CoA is replaced by a phosphate group, which forms GTP (later converted to ATP), yielding succinate, catalyzed by succinyl CoA synthetase.

What happens to succinate in the sixth step?

Succinate is oxidized by FAD to form fumarate and FADH2, catalyzed by succinate dehydrogenase.

What happens to fumarate in the seventh step?

Fumarate is converted to malate by adding a water molecule, catalyzed by fumarase.

What happens to malate in the eighth step?

Malate is oxidized by NAD+ to regenerate oxaloacetate, catalyzed by malate dehydrogenase.

Why does the citric acid cycle regenerate oxaloacetate?

Oxaloacetate is needed to combine with the next Acetyl CoA molecule, allowing the cycle to continue.

What are the energy-yielding products of one cycle turn?

3 NADH, 1 FADH2, and 1 ATP (or GTP).

How many NADH, FADH2, and ATP are produced from one glucose molecule?

6 NADH, 2 FADH2, and 2 ATP because one glucose produces two Acetyl CoA molecules.

Where do the NADH and FADH2 go after the citric acid cycle?

They carry electrons to the electron transport chain for ATP production.

What is the significance of the citric acid cycle in cellular respiration?

It generates high-energy electron carriers (NADH and FADH2) and ATP, crucial for producing energy in the next step, the electron transport chain.