Electron Transport Chain Lecture

Overview

The electron transport chain (ETC) is a series of complexes located in the inner mitochondrial membrane, crucial for cellular respiration. It facilitates the final stage of energy production, where ATP is synthesized using electrons derived from NADH and FADH2.(NADH IS 2e and hydrogen proton)

Mitochondrial Structure

• Outer Mitochondrial Membrane: Separates the mitochondrion from the cytosol.
• Inner Mitochondrial Membrane: Contains folds called cristae, where the ETC occurs.
• Intermembrane Space: Between outer and inner membranes.
• Mitochondrial Matrix: Inside the inner membrane; site of the Krebs cycle and other metabolic processes.

Key Processes

Glycolysis

• Glucose (6-carbon) is split into two pyruvate molecules (3-carbons each), generating 2 NADH and a net gain of 2 ATP. 2 NADH BY GLYCOLYSIS AND 2 FROM TRANSITION STEP

Pyruvate Conversion

• In the presence of oxygen, pyruvate enters the mitochondrial matrix and is converted to Acetyl-CoA by pyruvate dehydrogenase, producing an additional NADH.

Krebs Cycle

• Converts Acetyl-CoA to CO2, generating 6 NADH and 2 FADH2 per glucose molecule.
• NADH and FADH2 carry electrons to the ETC.

Electron Transport Chain Components

1. Complex I (NADH Dehydrogenase)

   • NADH is oxidized to NAD+, transferring electrons to fe sulphur clusters. They transfer to flavin mononucleotide (FMN), which reduces to FMNH2.
   • Electrons are passed to Coenzyme Q (COQ10)(ubiquinone), reducing it to CoQH2.(ubiquinol) these are mobile and protein less.
   • Proton pumping occurs from the matrix to the intermembrane space.

2. Complex II (Succinate Dehydrogenase)

   • FADH2 is oxidized to FAD, electrons are picked by FMN and converted to FMNH2 then transferring electrons directly to CoQ. And it is converted to QH2
   • No proton pumping occurs at this complex.

3. **Complex III (Cytochrome bc1 Complex)**or Coq-cyt reductase

   • CoQH2 transfers electrons to cytochrome b, then to cytochrome c.(also fe+3is converted into fe+2
   • Facilitates additional proton pumping into the intermembrane space.

4. Complex IV (Cytochrome Oxidase or a a3)

   • Cytochrome c transfers electrons and hydrogen from ims to oxygen, the final electron acceptor, forming water.(has fe or cu fe+3 to fe+2. CuA which transfers e from cyt c to a and CuB to bind oxygen and catalyse it to water (a3)
   • Additional protons are pumped into the intermembrane space.

Electron Transfer and Energy

• Electrons move from high to low energy states, facilitating the pumping of protons across the membrane, creating a proton gradient.
• The gradient is used to synthesize ATP in the next part of cellular respiration, which will be discussed in subsequent lectures.

Proton Gradient

• Established by:
  • Proton pumping at Complex I, III, and IV.
  • No protons are pumped at Complex II.
• Concentration Difference:
  • Intermembrane space: Higher proton concentration (10^-7 M).
  • Mitochondrial matrix: Lower proton concentration (10^-9 M).

Next Steps

• The next lecture will focus on how NADH from glycolysis enters the mitochondria for electron donation to the ETC.