TCA Cycle Quiz: Test Your Knowledge

What is the end product of the oxidation of acetyl CoA in the TCA cycle?

What is the site of the TCA cycle?

What is the immediate product of the reaction between acetyl CoA and oxaloacetate?

What is the significance of the TCA cycle in the synthesis of biomolecules?

What is the fate of cis-aconitate in the TCA cycle?

What is the net gain of ATP during the complete oxidation of glucose?

What is the product of the spontaneous decarboxylation of oxalosuccinate?

What is the role of malic enzyme in anaplerotic reactions?

What is the effect of arsenite on the TCA cycle?

What is the purpose of anaplerotic reactions in the TCA cycle?

What is the effect of ATP on citrate synthase?

TCA Cycle Overview

Also known as Kreb's cycle or Citric acid cycle
Final common oxidative pathway for carbohydrates, fats, and amino acids
Supplies energy and many intermediates for amino acid, glucose, and heme synthesis
Located in the mitochondrial matrix
Involves the oxidation of acetyl CoA to CO2 and H2O in a cyclic manner, generating ATP

Reactions of TCA Cycle

Acetyl CoA + Oxaloacetate → Citrate
Isocitrate → Oxalosuccinate → α-Ketoglutarate
α-Ketoglutarate → CO2 and NADH
Oxidation of acetyl CoA → CO2 and H2O

Energetics of TCA Cycle

Steps 4, 6, 10: 3 NADH = 9 ATP
Step 8: 1 FADH2 = 2 ATP
Step 7: 1 GTP = 1 ATP
Total ATP yield per acetyl CoA: 12 ATP
Total ATP yield per glucose: 38 ATP

Amphibolic Nature of TCA Cycle

Both catabolic and anabolic
Intermediates are used for amino acid, glucose, and heme synthesis
Examples of amphibolic reactions:
- Aspartate and purine synthesis from oxaloacetate
- Fatty acid and steroid synthesis from acetyl CoA
- α-Ketoglutarate and glutamate synthesis from transamination

Anaplerotic Reactions

Replenish TCA cycle intermediates
Examples:
- Pyruvate + CO2 + ATP → Oxaloacetate + ADP + Pi
- Pyruvate + CO2 + NADPH + H+ → Malate

Inhibitors of TCA Cycle Enzymes

Aconitase inhibited by fluoroacetate
α-Ketoglutarate dehydrogenase inhibited by arsenite
Succinate dehydrogenase inhibited by malonate

Regulation of TCA Cycle

Citrate synthase inhibited by ATP, NADH, acyl CoA, and succinyl CoA

Test your understanding of the tricarboxylic acid cycle (TCA cycle), also known as Kreb's cycle or citric acid cycle, and its role in energy production and synthesis of amino acids, glucose, and heme. Calculate the energy yield per turn of the cycle and describe the further processing of acetyl-CoA.