Metabolism and Energy Production Process Notes

  • Overview of Metabolism Stages

    • Stage 1 (Intestines): Breakdown of polysaccharides into smaller units.
    • Stage 2 (Cell): Glycolysis, where glucose is converted into pyruvate.
    • Stage 3 (Mitochondria): Citric Acid Cycle and Electron Transport Chain, where further energy production occurs.

  • Energy Production

    • Each ATP molecule produced releases approximately 7.3 kilocalories.
    • ATP Forms:
    • AMP (Adenosine Monophosphate)
    • ADP (Adenosine Diphosphate)
    • ATP (Adenosine Triphosphate)
    • ATP is considered a high energy molecule, while ADP is lower in energy.

  • Oxygen and Cellular Metabolism

    • Oxidation: Releases energy, involves loss of electrons and hydrogen atoms.
    • Reduction: Requires energy, involves gain of electrons and hydrogen.
    • Key Coenzymes:
    • NAD+/NADH (Nicotinamide Adenine Dinucleotide): Goes from low energy form (NAD+) to high energy (NADH).
    • FAD/FADH₂ (Flavin Adenine Dinucleotide): Low energy (FAD) to high energy (FADH₂).

  • Key Enzymes and Vitamins

    • Coenzyme A: Important in fatty acid metabolism; derived from Pantothenic Acid (Vitamin B5).
    • NAD+: Derived from Niacin (Vitamin B3).
    • FAD: Associated with Vitamin B2 (Riboflavin).

  • Glycolysis

    • Phases:
    • Energy Investment Phase (Steps 1-5): Consumes ATP.
    • Energy Generation Phase (Steps 6-10): Produces ATP and NADH.
    • Key Outcomes:
    • From 1 glucose, glycolysis yields 2 pyruvate, 2 ATP, and 2 NADH.
    • Total ATP generated can differ based on context (7 or 5 ATP via NADH).
    • Reaction Summary:
    • Substrates: 1 Glucose + 2 NAD^+ + 2 ADP + 2 P_i
    • Products: 2 Pyruvate + 2 NADH + 2 ATP + some H⁺ and H₂O.

  • Citric Acid Cycle (Krebs Cycle)

    • Occurs in the mitochondria under aerobic conditions.
    • Function: Converts acetyl-CoA into energy carriers: NADH, FADH₂, and GTP.
    • Key Outputs: Each cycle produces:
    • 2 CO₂
    • 3 NADH
    • 1 FADH₂
    • 1 GTP
    • Main Steps:
    • Forming citrate from acetyl-CoA and oxaloacetate, followed by a series of decarboxylation reactions.

  • Electron Transport Chain

    • Located in mitochondrial inner membrane with five complexes (I - V).
    • Function: Transferring electrons from NADH and FADH₂ to oxygen, creating a proton gradient for ATP synthesis.
    • ATP Synthesis Mechanism: Protons flow back through ATP synthase (Complex V) to drive ATP production.
    • End Products: Up to 28 ATP from one molecule of glucose after all processes.

  • Regulation of Metabolism

    • Key regulatory points located at glycolysis stages (hexokinase, phosphofructokinase, and pyruvate kinase).
    • Hormonal control by Insulin (promotes glycolysis and glycogenesis) and Glucagon (promotes glycogenolysis).

  • Anaerobic Conditions

    • In absence of oxygen, pyruvate is converted to lactate (in muscles) or ethanol (in yeast).
    • Cori Cycle: Lactate produced by muscles is transported to the liver, converted back to glucose via gluconeogenesis, and sent back for muscle use.

  • Glycogen Metabolism

    • Glycogenesis: Glucose molecules are stored as glycogen in liver and muscle tissues.
    • Glycogenolysis: Breakdown of glycogen to release glucose into the bloodstream, triggered by glucagon.

  • Gluconeogenesis

    • The formation of glucose from non-carbohydrate sources (like pyruvate) when the body needs glucose and there are low carbohydrate resources available.
    • Requires more energy input than glycolysis produces.

  • Key Takeaway

    • Understanding the interconnected pathways of energy metabolism helps in translating physiological energy needs and responses to varying dietary conditions and physical activities.