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Cellular Respiration: Krebs Cycle Notes

Cellular Respiration: Krebs Cycle

Overview

  • Cellular respiration involves oxidizing glucose to produce ATP.
  • Key processes include glycolysis and the Krebs cycle, which generate reducing power (NADH and FADH2).
  • Chemiosmosis converts the reducing power of NADH and FADH2 into ATP.
  • These processes occur in the mitochondrion.
  • Distinction between aerobic and anaerobic respiration and fermentation.
  • ATP plays a central role in cellular metabolism.

Lesson 3: Krebs Cycle - Key Questions

  1. What is pyruvate oxidation?
  2. What are the reactants and products of the Krebs cycle?

Glycolysis Review

  • Location: Cytoplasm (cytosol)
  • Products:
    • 2 ATP
    • 2 NADH
    • 2 Pyruvate molecules
  • Fate in Absence of Oxygen: Fermentation

Aerobic Respiration

  • Four main steps to produce ATP:
    • Glycolysis (anaerobic and aerobic)
    • Pyruvate Oxidation (Pre-Krebs)
    • Krebs Cycle
    • Electron Transport Chain (ETC) and Chemiosmosis

Pre-Kreb’s Cycle (Pyruvate Oxidation)

  • Occurs if oxygen is present after glycolysis.
  • Location: Matrix of the mitochondria.
  • Purpose: To modify pyruvate to produce Acetyl CoA.

Process:

  • Pyruvate loses one carbon atom in the form of carbon dioxide (CO_2).
  • The remaining two carbon atoms bind to Coenzyme A (CoA) to form Acetyl CoA.
  • This reaction reduces NAD^+ to NADH.
  • Acetyl CoA initiates the Krebs Cycle.

Steps:

  • Pyruvate enters mitochondria.
  • Loses a carbon atom to form CO_2.
  • NAD^+ reduces to NADH.
  • Bonds with coenzyme A (CoA) to form acetyl CoA.

Pyruvate Oxidation: End Products (from 2 Pyruvates)

  • 2 NADH
  • 2 CO_2
  • 2 Acetyl CoA (2 Carbon atoms each)

Krebs Cycle (Citric Acid Cycle)

  • Main Purpose: To produce more high-energy compounds (NADH & FADH2).
  • NADH and FADH2 are used in the Electron Transport Chain (ETC) and chemiosmosis.

Process:

  • Acetyl CoA undergoes a series of reactions.
  • Products (per cycle):
    • 3 molecules of NADH from NAD^+
    • 1 molecule of ATP from ADP
    • 1 molecule of FADH2 from FAD
    • CO_2 is released as a by-product
  • Occurs in 8 steps

Krebs Cycle Summary

Molecules Produced During a Single Krebs Cycle:

  • 3 NADH
  • 1 FADH2
  • 2 CO_2
  • 1 ATP
  • Note: The Krebs cycle occurs twice per each molecule of glucose.

Kreb Cycle Overview

  • This cycle creates a small amount of ATP.
  • By the end of the Kreb’s Cycle, ALL 6 carbon atoms in the glucose have been oxidized and released in the form of CO_2.
  • From the breakdown of glucose, energy in the form of ATP and high energy molecules, NADH and FADH2, have been produced.
  • NADH and FADH2 will be used for the next step, which is the ETC and chemiosmosis.