Carbohydrate Metabolism Summary

Carbohydrate Metabolism Overview

• All carbohydrates are converted to glucose.
• Overall glucose oxidation reaction: $C<em>{6}H</em>{12}O<em>{6} + 6O</em>{2} \rightarrow 6H<em>{2}O + 6CO</em>{2} + 32 ATP + heat$
• Glucose catabolism occurs via three main pathways:
  • Glycolysis
  • Anaerobic fermentation
  • Aerobic respiration (Krebs cycle, Electron Transport Chain)
• Key coenzymes: Nicotinamide adenine dinucleotide (NAD+), Flavin adenine dinucleotide (FAD).

Glycolysis

• Location: Cytoplasm.
• Condition: Anaerobic or aerobic.
• Process: Glucose (6C) is split into two pyruvate molecules (3C).
• Products per glucose: 2 pyruvate, 2 NADH, 2 net ATP.
• Phases: Sugar activation, sugar cleavage, sugar oxidation and ATP formation.

Anaerobic Fermentation

• Occurs in the absence of oxygen.
• Reduces pyruvate to lactate.

Aerobic Respiration

• Occurs in the presence of oxygen.
• Oxidizes pyruvate to $CO<em>{2}$ and $H</em>{2}O$.

Krebs Cycle (Citric Acid Cycle)

• Location: Mitochondrial matrix.
• Condition: Aerobic only.
• Input: Acetyl-CoA (from pyruvate).
• Products per glucose (for two Acetyl-CoA): $6CO_{2}$, 8 NADH, 2 FADH2, 2 ATP.
• Reversibility: Irreversible.

Electron Transport Chain (ETC) and Oxidative Phosphorylation

• Location: Inner mitochondrial membrane (Cristae).
• Condition: Aerobic only.
• Mechanism: NADH and FADH2 deliver electrons. Energy from electron transfer pumps $H^{+}$ into the intermembrane space. $H^{+}$ flows back into the matrix through ATP synthase, generating ATP (chemiosmosis).
• Final electron acceptor: Oxygen ($O<em>{2}$), forming water ($H</em>{2}O$).
• ATP Yield: 28 ATP per glucose.
  • 1 NADH produces $2.5 ATP$.
  • 1 FADH2 produces $1.5 ATP$.

Total ATP Production Per Glucose

• Glycolysis: 2 ATP
• Citric Acid Cycle: 2 ATP
• Electron Transport Chain: 28 ATP
• Total: 32 ATP

Glucose Regulation Processes

• Glycogenesis: Glucose molecules combine to form glycogen (storage).
• Glycogenolysis: Glycogen molecules are broken down to form glucose.
• Gluconeogenesis: Forming new glucose from non-carbohydrate molecules (occurs in liver).