Citric Acid Cycle

Introduction

• The citric acid cycle, also known as the Krebs cycle or TCA cycle (Tricarboxylic Acid Cycle), is a crucial part of cellular respiration.
• It takes place in the mitochondria's matrix, specifically after glycolysis, but only under aerobic conditions (in the presence of oxygen).

Key Steps in the Citric Acid Cycle

1. Formation of Acetyl Coenzyme A

• Pyruvate, produced in glycolysis, enters the mitochondria's matrix.
• During this process, carbon dioxide is removed from pyruvate, resulting in the formation of an acetyl group.
• The acetyl group combines with coenzyme A (CoA) to form acetyl coenzyme A (acetyl-CoA).

2. Citrate Formation

• Acetyl-CoA combines with oxaloacetate to form citrate, which gives the cycle its name.

3. Intermediate Molecules

• During the cycle, enzymes remove carbon (in the form of carbon dioxide) and hydrogen/electrons from intermediate molecules.
• These reactions lead to the gradual conversion of citrate back into oxaloacetate.

4. Release of Carbon Dioxide

• Carbon dioxide is released as a by-product during the cycle.

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Citric Acid Cycle

5. ATP Production

• The citric acid cycle results in the production of ATP, the cell's primary energy currency.

6. NADH Formation

• Dehydrogenase enzymes remove hydrogen ions and electrons from intermediate molecules.
• These electrons are passed to coenzymes NAD (forming NADH), carrying high-energy electrons.

7. Electron Transport Chain

• The high-energy electrons carried by NADH are transferred to the electron transport chain, located on the inner mitochondrial membrane.