Carbohydrate Metabolism: Electron Transport Chain and Oxidative Phosphorylation

Introduction

• Presenter: Iman
• Focus: Cellular respiration, specifically electron transport chain and oxidative phosphorylation
• Context: Harvesting energy from glucose to produce ATP

Review of Previous Steps

• Glycolysis: Produces 2 net ATP
• Citric Acid Cycle: Produces 2 net ATP
• NADH and FADH2: Account for most energy extracted from glucose so far

Electron Transport Chain (ETC)

• Location: Inner mitochondrial membrane
• Function: Series of redox reactions to transfer electrons and generate ATP
• Components: Multi-protein complexes (I, II, III, IV)

Complex I (NADH Dehydrogenase)

• Role: Accepts electrons from NADH
• Mechanism: Uses iron-sulfur clusters to transfer electrons to Coenzyme Q (CoQ)
• Proton Pumping: Pumps H+ across the membrane

Complex II (Succinate Dehydrogenase)

• Role: Accepts electrons from succinate
• Mechanism: Transfers electrons from succinate to CoQ, first to FAD, then to CoQ
• No Proton Pumping

Complex III (Cytochrome bc1 Complex)

• Role: Receives electrons from CoQ
• Mechanism: Transfers electrons to Cytochrome C
• Proton Pumping: Pumps H+ across the membrane

Complex IV (Cytochrome C Oxidase)

• Role: Transfers electrons to molecular oxygen
• Mechanism: Reduces O2 to form water
• Proton Pumping: Pumps H+ across the membrane

Proton Gradient and Electrochemical Gradient

• Formation: H+ pumping creates gradient
• Effects:
  • pH drops in intermembrane space
  • Electrochemical gradient known as proton motive force

ATP Synthase and Chemo Osmosis

• Location: Inner mitochondrial membrane
• Function: Uses proton motive force to synthesize ATP
• Mechanism: H+ ions drive the synthesis of ATP from ADP and inorganic phosphate
• Steps:
  1. H+ enters stator
  2. Moves to rotor, causes changes in subunits
  3. Completes a turn, exits rotor, passes through internal rod
  4. Activates catalytic sites, pairs ADP with phosphate to form ATP

NADH Shuttle Mechanisms

• Issue: NADH cannot cross inner mitochondrial membrane
• Shuttles:
  • Glycerol 3-Phosphate Shuttle: Transfers electrons from NADH to DHAP to G3P, then to mitochondrial FAD
  • Malate Aspartate Shuttle: Transfers electrons from NADH to oxaloacetate to form malate, which transfers electrons to mitochondrial NAD+

Summary of Steps in Cellular Respiration

1. Glycolysis (Cytoplasm)

• Input: Glucose, 2 ATP, 2 NAD+
  • Output: 2 pyruvate, 4 ATP, 2 NADH
  • Net: 2 ATP, 2 NADH

2. Citric Acid Cycle (Mitochondrial Matrix)

• Input: 2 Acetyl-CoA
  • Output per cycle: 2 CO2, 3 NADH, 1 FADH2, 1 ATP
  • Net per Glucose: 4 CO2, 6 NADH, 2 FADH2, 2 ATP

3. Electron Transport Chain and Oxidative Phosphorylation (Inner Mitochondrial Membrane)

• Input: NADH, FADH2
  • Output: Water, 32-34 ATP

Overall ATP Yield

• Glycolysis + Citric Acid Cycle + ETC: 36-38 ATP per glucose molecule

Conclusion

• The final yield of ATP in cellular respiration is approximately 36-38 ATP molecules.
• Importance of understanding glucose metabolism and ATP production

Closing

• Encouragement for questions and further study
• Wish for success and a good day