1. Glycolysis (Cytoplasm):
* Glucose (6 carbons) enters the cytoplasm.
* Through a series of enzyme-catalyzed reactions, glucose is broken down into two molecules of pyruvate (3 carbons each).
* This process generates a net gain of 2 ATP and 2 NADH (electron carriers).
2. Pyruvate Oxidation (Mitochondrial Matrix):
* Pyruvate enters the mitochondria, where it is converted into acetyl-CoA (2 carbons) by losing a carbon dioxide molecule.
* This process generates 1 NADH per pyruvate, so 2 NADH in total.
3. Citric Acid Cycle (Krebs Cycle) (Mitochondrial Matrix):
* Acetyl-CoA enters the citric acid cycle, a series of reactions that produce high-energy electron carriers and carbon dioxide.
* Each acetyl-CoA molecule produces:
* 3 NADH
* 1 FADH2 (another electron carrier)
* 1 ATP
* 2 CO2
* Since two acetyl-CoA molecules are formed from one glucose, the total yield is:
* 6 NADH
* 2 FADH2
* 2 ATP
* 4 CO2
4. Oxidative Phosphorylation (Electron Transport Chain and Chemiosmosis) (Inner Mitochondrial Membrane):
* The electron carriers (NADH and FADH2) deliver their electrons to the electron transport chain.
* As electrons move through the chain, energy is released and used to pump protons (H+) across the inner mitochondrial membrane, creating a proton gradient.
* This gradient drives ATP synthesis by ATP synthase, which uses the energy from the proton flow to add a phosphate group to ADP, producing ATP.
* This is the major ATP-producing stage of respiration.
Final ATP Yield:
* Glycolysis: 2 ATP
* Citric Acid Cycle: 2 ATP
* Oxidative Phosphorylation: ~32 ATP (theoretically 38, but some protons are "leaked")
Total ATP Yield: 36 ATP
Note: This is a simplified overview. The actual number of ATP produced can vary slightly depending on the specific conditions and cell type.
Summary:
Aerobic respiration is a complex process that efficiently extracts energy from glucose to produce ATP, the primary energy currency of cells. It involves a series of carefully coordinated steps in different parts of the cell, utilizing electron carriers and proton gradients to achieve high energy yield.
