Lecture Notes: Electron Transport Chain and ATP Synthesis

Introduction

• The lecture focuses on the electron transport chain, a critical part of cellular respiration in both bacteria and eukaryotes.
• The process involves NADH and FADH2, which have been generated through glycolysis, linking steps, and the citric acid cycle.

Electron Transport Chain (ETC)

• Location: Plasma membrane (in bacteria) or mitochondrial membrane (in eukaryotes).
• Key Complexes:
  • Complex I (NADH dehydrogenase): Accepts electrons from NADH, pumps protons to create a proton gradient.
  • Complex II (Flavin mononucleotide): Accepts electrons from FADH2.
  • Complex III (Coenzyme Q): Shuttles electrons to cytochrome complex.
  • Complex IV (Cytochrome): Transfers electrons to oxygen, reducing it to water.
• Proton Motive Force (PMF): Created by the transfer of electrons through complexes, pumping protons and establishing an electrochemical gradient.

Electron Flow

• NADH Pathway:
  • Electrons go from Complex I to III to IV.
  • Proton pumping occurs at Complex I, III, and IV.
• FADH2 Pathway:
  • Electrons start at Complex II, then to III, and IV.
  • Fewer protons are pumped as it skips Complex I.

Role of Oxygen

• Oxygen as Final Electron Acceptor:
  • Combines with protons and electrons to form water.
  • Allows the ETC to continue functioning.

ATP Synthesis

• ATP Synthase:
  • Located in the membrane, consisting of F0 (motor) and F1 (catalytic) portions.
  • Uses proton motive force to drive the synthesis of ATP from ADP and inorganic phosphate.
  • F0 Portion: Acts as a channel for protons, causing the entire complex to spin.
  • F1 Portion: Catalyzes the formation of ATP.
  • Full rotation of F0 results in the production of 3 ATP molecules.

Efficiency of ATP Production

• NADH Yields: 3 ATP per molecule.
• FADH2 Yields: 2 ATP per molecule.
• Total ATP from Electron Transport Chain:
  • 10 NADH x 3 ATP = 30 ATP
  • 2 FADH2 x 2 ATP = 4 ATP
  • Total: 34 ATP from oxidative phosphorylation.

Anabolism

• Purpose of ATP and Energy:
  • Cells use ATP for biosynthesis pathways like gluconeogenesis and the pentose phosphate pathway.
  • Energy is required to synthesize cell components like sugars, nucleotides, amino acids, and fatty acids.
  • These processes are essential for cell growth and division.

Summary

• The electron transport chain is crucial for establishing the proton motive force required for ATP synthesis.
• ATP synthase efficiently utilizes this force to produce ATP, crucial for various cellular anabolic processes.