(1) Pyruvate processing

Overview of Cellular Respiration

  • Focus on the second phase: Pyruvate Processing (abbreviated as Pipi).

Location and Process

  • Occurs within the mitochondrial matrix.

  • Pyruvate Transport:

    • Pyruvate is produced from glycolysis and enters mitochondria.

    • Moves across the outer membrane and through pores into the matrix using a pyruvate carrier (membrane protein).

    • Active Process: Requires ATP to transport pyruvate, illustrating the principle of spending energy to generate energy.

Stages of Pyruvate Processing

  1. Formation of Acetyl CoA:

    • Pyruvate reacts with Coenzyme A (CoA).

    • Results in the formation of Acetyl Coenzyme A (acetyl CoA).

    • This involves transferring an acetyl group from pyruvate to coenzyme A.

  2. Oxidation of Pyruvate:

    • One carbon atom from pyruvate is oxidized.

    • This process results in the reduction of NAD+ to NADH (loss of electrons).

  3. Formation of Citrate:

    • Acetyl CoA reacts with oxaloacetate to form citrate.

    • Citrate is the first component of the Krebs cycle, to be discussed in the next lecture.

Regulation of Pyruvate Processing

  • Pyruvate processing is regulated like glycolysis.

  • It is inhibited when ATP levels are high:

    • ATP Binding: Causes a change in shape of the pyruvate dehydrogenase enzyme, leading to phosphorylation and stopping the process.

  • Increased concentrations of acetyl CoA and NADH also promote the rate of phosphorylation, indicating a shift towards ATP production when ATP is low.

Summary of Products from Pyruvate Processing

  • Inputs: 2 pyruvates, 2 NAD+, and 2 CoA.

  • Outputs: 2 carbon dioxide molecules, 2 NADH, and 2 acetyl CoA.

  • Key point: Unlike glycolysis, pyruvate processing takes place in the mitochondrial matrix.