Tricarboxylic Acid Cycle

What is the main purpose of cellular respiration?

To consume O₂ and produce CO₂ while generating ATP from the breakdown of carbohydrates, fats, and proteins.

What are the three stages of cellular respiration?

(1) Acetyl-CoA production, (2) Acetyl-CoA oxidation, (3) Electron transfer & oxidative phosphorylation.

Where is Acetyl-CoA produced in the cell?

In the mitochondrial matrix.

What enzyme complex converts pyruvate into Acetyl-CoA?

Pyruvate dehydrogenase complex.

What is the function of Coenzyme A (CoA)?

It has a reactive thiol group that forms a thioester bond with acetyl groups for entry into the TCA cycle.

What is the first step of the TCA cycle?

Condensation of Acetyl-CoA with Oxaloacetate to form Citrate.

What is the function of isocitrate dehydrogenase?

Catalyzes oxidative decarboxylation of isocitrate to α-ketoglutarate, producing NADH.

What is the key regulatory enzyme that converts α-ketoglutarate to succinyl-CoA?

α-Ketoglutarate dehydrogenase.

Which TCA enzyme is involved in substrate-level phosphorylation?

Succinyl-CoA synthetase (forms GTP from GDP).

What enzyme catalyzes the conversion of succinate to fumarate?

Succinate dehydrogenase.

What are the total products of one turn of the TCA cycle?

2 CO₂, 3 NADH, 1 FADH₂, 1 GTP (or ATP), and 1 CoA.

How much ATP is ultimately produced from 1 glucose via aerobic respiration?

Approximately 30–32 ATP.

What is the amphibolic role of the TCA cycle?

It serves both catabolic and anabolic functions; intermediates are used in biosynthetic pathways.

What are anaplerotic reactions?

Reactions that replenish TCA cycle intermediates.

Which TCA cycle steps are highly regulated?

Steps catalyzed by citrate synthase, isocitrate dehydrogenase, and α-ketoglutarate dehydrogenase.

What inhibits the TCA cycle?

High levels of ATP, NADH, and citrate.

What activates the TCA cycle?

Substrate availability (e.g., ADP, NAD⁺, Ca²⁺).