ATP Production- Lecture

Cellular Respiration and ATP Synthesis

Overview of Mitochondrial Function

  • Proton gradient creation in mitochondrial membranes.

  • Stator: Stationary components consisting of:

    • Long rod extending into the matrix.

    • Catalytic knob (stationary) supported by an arm.

  • Rotor: Moves as protons bind and induce rotation.

Proton Channels and ATP Formation

  • Proton Channels: Allow protons to move through the membrane.

    • Protons bind to rotor, facilitating its movement.

    • Complete rotation needed for protons to enter the mitochondrial matrix.

  • Protons pumped back into the intermembrane space after ATP synthesis.

ATP Generation Mechanism

  • Drives the internal rotor and rod, inducing phosphorylation reactions at catalytic knobs.

  • Phosphorylation Process:

    • Inorganic phosphate is covalently attached to ADP to form ATP.

    • Key Point: 4 protons equate to the synthesis of 1 ATP molecule.

Steps in Cellular Respiration

  1. Glycolysis: Occurs in cytosol with a net gain of 2 ATP via substrate-level phosphorylation.

  2. Pyruvate Dehydrogenase Complex: Converts pyruvate into acetyl-CoA.

  3. TCA Cycle: Also known as Krebs cycle.

Yield of ATP from Glycolysis

  • ATP Production:

    • Investment Phase: Consumes 2 ATP.

    • Payoff Phase: Produces 4 ATP.

    • Result: Net gain = 2 ATP via substrate-level phosphorylation.

  • Reducing Equivalents: Production of NADH and FADH2.

    • Mobile electron carriers transport electrons to the ETC.

Mobile Electron Carriers**

  • NADH / FADH2: Collect and transfer electrons from glycolysis to the electron transport chain (ETC).

  • Oxidized Form: NAD+ (empty, can accept electrons).

  • Reduced Form: NADH (filled, has electrons).

ATP Produced from NADH and FADH2

  • Each NADH generates approximately 2.5 ATP:

    • 10 protons pumped per NADH.

    • 4 protons = 1 ATP.

    • 10 protons lead to about 2.5 ATP.

  • Total from two NADH: 2 × 2.5 = 5 ATP.

Shuttle Mechanisms for Electrons

  • Malate-Aspartate Shuttle: Transfers NADH from cytosol to mitochondrial matrix, converting it back to NADH in the matrix.

  • 3-Phosphoglycerol Shuttle: Transfers electrons as FADH2 instead; drops them at complex two.

    • Result: Different ATP yields depending on transport shuttle used.

  • Understanding these shuttles is critical for accurate ATP calculations throughout cellular respiration.