Overview of ATP Synthesis

• The energy currency of the cell is ATP.

Summary of Part Three: ATP Synthesis

• Focuses on the conversion of glucose to ATP through various biochemical processes.
• Key products: ATP, NADH, FADH2.
• Key stages: Glycolysis, Krebs Cycle (Citric Acid Cycle), Electron Transport Chain.

Glycolysis

• Location: Cytoplasm
• Overview: Breakdown of glucose into two pyruvic acids.
• Phases:
    - Investment Phase:
      - Energy investment required to initiate glycolysis.
      - ATP is consumed to convert glucose into glucose-6-phosphate.
    - Cleavage Phase:
      - Fructose-1,6-bisphosphate is cleaved into two three-carbon molecules (Glyceraldehyde-3-phosphate).
    - Energy Harvest Phase:
      - Produces ATP and NADH.
      - Net gain: 2 ATP produced from the investment of 2 ATP (4 total produced - 2 invested).
• Final Products of Glycolysis:
    - 2 Pyruvic acids,
    - 2 NADH,
    - 2 ATP.

Anaerobic Respiration

• Occurs in the absence of oxygen.
• Pyruvic acids converted to lactic acid.
• ATP yield: 2 ATP per glucose.

Aerobic Respiration

• Presence of oxygen allows for complete oxidation of glucose.
• Through aerobic respiration, up to 38 ATP can be produced per glucose molecule.

Aerobic Respiration Process

• Stage 1: Conversion of glucose to pyruvic acids (identical to glycolysis).
• Stage 2: Conversion of pyruvic acid to acetyl coenzyme A:
    - Produces 2 NADH and releases CO2.
• Stage 3: Krebs Cycle (Citric Acid Cycle).

Krebs Cycle (Citric Acid Cycle)

• Location: Mitochondrial matrix.
• Process: Acetyl coenzyme A enters Krebs Cycle.
• Key Reactions:
    - Isomerization: Changes shape without altering atomic composition (e.g. citric acid to isocitric acid).
    - Oxidative Decarboxylation: Removal of CO2 while producing NADH (e.g. isocitric acid to alpha-ketoglutaric acid).
    - Substrate Level Phosphorylation: Direct ATP production from succinyl coenzyme A to succinic acid.
    - Dehydrogenation: Release of hydrogen atoms (e.g. FADH2 production).
    - Hydration: Addition of water to the molecule.
    - Final Dehydrogenation: Further removal of hydrogens, producing additional NADH.

Mnemonic for Krebs Cycle Compounds

• Sequence: Citric acid, Isocitric acid, Alpha-ketoglutaric acid, Succinyl CoA, Succinic acid, Fumaric acid, Malic acid, Oxaloacetic acid.
• Mnemonic Example: "Can I Keep Selling Sex For Money Officer?"

Products of the Krebs Cycle

• Reactants include: Acetyl CoA, NAD+, FAD, ADP.
• Products include: NADH, FADH2, ATP, CO2.

Electron Transport Chain (ETC)

• Location: Inner mitochondrial membrane.
• Process:
    - Uses NADH and FADH2 produced from earlier stages to transport electrons.
    - ATP Synthase: Key enzyme facilitating ATP production as protons (H+) flow back into the mitochondrial matrix.
• Key Outcomes:
    - Conversion of electron energy into a proton gradient.
    - ATP generation (32-34 ATP from one glucose molecule).
    - Water is produced when O2 combines with electrons and protons (hydrogens).

Importance of Oxygen

• Oxygen serves as the final electron acceptor.
• Why we breathe: Oxygen's role in electron transport chain is crucial for ATP production;
• Absence of oxygen (no ETC) drastically reduces ATP synthesis.

Summary of Phases in Order

1. Glycolysis (Glucose to Pyruvic Acid)
2. Acetyl CoA Formation (from Pyruvic Acid)
3. Krebs Cycle (Citric Acid Cycle)
4. Electron Transport Chain