Glucose Metabolism and Citric Acid Cycle

Glucose Metabolism

Glycolysis

• Converts glucose (6-carbon sugar) into pyruvate (3-carbon molecule)
• Occurs in cytosol of cells
• Generates 2 ATP and 2 NADH molecules
• Can occur in absence of oxygen (anaerobic) or presence of oxygen (aerobic)

Pyruvate Oxidation

• Converts pyruvate into acetyl-CoA
• Occurs in mitochondria
• Generates 2 NADH molecules
• Acetyl-CoA enters citric acid cycle

Glycogen Synthesis and Breakdown

• Glycogen is a stored form of glucose in liver and muscles
• Glycogen synthesis: glucose is converted into glycogen
• Glycogen breakdown: glycogen is converted into glucose
• Regulated by hormones (insulin and glucagon)

Citric Acid Cycle (Krebs Cycle or Tricarboxylic Acid Cycle)

Overview

• Also known as Krebs cycle or tricarboxylic acid (TCA) cycle
• Occurs in mitochondria
• Generates ATP, NADH, and FADH2 molecules

Steps

1. Acetyl-CoA is converted into citrate
2. Citrate is converted into isocitrate
3. Isocitrate is converted into α-ketoglutarate
4. α-Ketoglutarate is converted into succinyl-CoA
5. Succinyl-CoA is converted into succinate
6. Succinate is converted into fumarate
7. Fumarate is converted into malate
8. Malate is converted into oxaloacetate
9. Oxaloacetate is converted into citrate, repeating the cycle

Products

• ATP: 2 molecules generated directly
• NADH: 6 molecules generated
• FADH2: 2 molecules generated
• Coenzyme A (CoA): regenerated for reuse