Recording-2025-02-19T20:00:20

Overview of Metabolism Phases

• Phase 1: Glycolysis

  • 10 reactions converting glucose (6 carbon) into two pyruvate (3 carbon) molecules.

  • Minimal energy is released; no CO2 or water are produced.

  • Potential energy remains in the food molecules.

• Phase 2: Pyruvate Oxidation and Krebs Cycle (Citric Acid Cycle)

  • Pyruvate is oxidized and CO2 is produced.

  • Energy extraction continues as carbons are fully respired out (breathing out).

  • Key reactions occur in the mitochondria.

• Phase 3: Electron Transport Chain and Chemiosmosis

  • Oxygen serves as the terminal electron acceptor, combining with protons and electrons, producing water.

  • ATP synthesis primarily occurs through oxidative phosphorylation.

  • Electron transport chains are crucial for creating proton gradients, not directly for ATP production.

Energy Capture Mechanisms

• Substrate Level Phosphorylation

  • Accounts for some ATP production during glycolysis and Krebs cycle but less efficient

• Oxidative Phosphorylation

  • Major ATP production method derived from the electrochemical gradient created by the electron transport chain.

  • ATP synthase (machine) synthesizes ATP from ADP and inorganic phosphate through chemiosmosis.

Understanding ATP Production

• Functional Importance of Enzymes

  • Enzymes are regulated based on the availability of substrates and the need for product.

  • Allosteric regulation allows enzymes to either ramp up or decrease their activity based on the cellular conditions.

• Fermentation Process

  • Occurs when oxygen (terminal electron acceptor) is limited, primarily after glycolysis.

  • No ATP is produced during fermentation; its purpose is to regenerate NAD+ from NADH to keep glycolysis operational.

  • Fermentation can increase glycolysis rates significantly—10 to 20 times faster.

Types of Fermentation

• Alcoholic Fermentation

  • Performed by yeast (e.g., brewer's yeast) producing ethanol and CO2.

  • Exploited in brewing and baking industries.

• Lactic Acid Fermentation

  • Occurs in human muscle cells when oxygen is scarce, producing lactic acid.

  • Responsible for muscle fatigue during strenuous activity; lactic acid is eventually transported to the liver for processing.

Metabolic Flexibility

• Humans can utilize carbohydrates, fats, and proteins for energy.

• Amino acids from proteins can enter metabolic pathways after deamination, connecting to glycolysis or Krebs cycle.

• Fatty acids are converted into acetyl CoA, feeding directly into the Krebs cycle, showcasing metabolic efficiency without needing separate extensive pathways for each type.

Cellular Impact of Low Oxygen

• Without oxygen, aerobic organisms can only rely on glycolysis, reducing ATP yield significantly (36 to 2 ATP per glucose).

• Rapid glycolysis may deplete food and result in cell death if oxygen is not restored.

Enzyme Regulation Mechanisms

• Allosteric Regulation

  • Regulatory molecules bind to allosteric sites, changing conformational shape, either activating or inhibiting enzyme functionalities.

  • Feedback inhibition occurs when the end product of a metabolic pathway inhibits an upstream process to maintain balance.

Key Enzymatic Example in Glycolysis

• Fructose-1,6-bisphosphate formation represents regulatory point:

  • High ATP levels signal to slow down glycolysis, while high ADP levels stimulate activity, illustrating the balance of energy needs in cell metabolism.