EB

Control of Enzyme Activity & Energy Production

Control of Enzyme Activity

  • Enzyme activity is highly sensitive to several factors:
    • Temperature
    • pH
    • Concentration of substrate
    • Stimulatory effects
    • Inhibitory effects

Energy for Life: Metabolic Pathways

  • The primary goal is to trap energy for life.
  • Photosynthesis: Produces glucose.
  • Glucose Metabolism: Glucose is processed through glycolysis to yield pyruvate.
  • Aerobic Respiration (Cellular Respiration):
    • Involves complete oxidation of glucose.
    • Waste products are H2O and CO2.
    • Net energy trapped: 32 ATP.
  • Anaerobic Respiration (Fermentation):
    • Involves incomplete oxidation.
    • Can produce lactate or alcohol.
    • Waste products include organic compounds and CO_2.
    • Net energy trapped: 2 ATP.

Oxidation and Reduction in Metabolic Pathways

  • Oxidation and reduction are coupled processes, meaning they occur together.
    • A reduced compound has gained electrons.
    • An oxidized compound has lost electrons (is missing electrons).
  • NAD+ acts as an electron transporter; it is reduced to NADH when it gains electrons.

Glucose Metabolism Flow

  • Glucose is stored in the liver as glycogen.
  • Blood Plasma: Glucose is transported in the blood plasma.
  • Glycogen Breakdown: Glycogen from the liver is broken down into glucose.
  • Cellular Uptake: Glucose travels through the blood to the cytoplasm of cells.
  • Glycolysis: Glucose then undergoes glycolysis, breaking down into pyruvic acid.
  • Pathways from Pyruvic Acid:
    • Anaerobic: Pyruvic acid is converted into lactic acid.
    • Aerobic Respiration: Pyruvic acid enters the mitochondrion, proceeds through the citric acid cycle, and is then used in the electron transport chain.

The Cori Cycle (Skeletal Muscles and Liver)

  • This cycle describes the inter-organ cooperation in lactate metabolism during and after exercise.
    1. Exercise (Skeletal Muscles): During exercise, glucose-6-phosphate is metabolized, leading to the production of lactic acid.
    2. Lactic Acid Release: Lactic acid enters the bloodstream.
    3. Transport to Liver: The blood carries lactic acid to the liver.
    4. Conversion in Liver: In the liver, lactic acid is converted to pyruvic acid.
    5. Gluconeogenesis: Pyruvic acid in the liver is then converted into glucose-6-phosphate, which can be further converted to glucose.
    6. Glucose Release: Glucose is released from the liver into the blood.
    7. Uptake by Muscles: Glucose returns to resting skeletal muscles for storage or energy use.

Glycolysis

  • Definition: Glycolysis is the metabolic pathway that converts glucose into pyruvate.
  • Key Enzymes in Energy-Investing Reactions:
    • Hexokinase
    • Phosphofructokinase
    • Phosphohexose isomerase
    • Aldolase
  • Hexokinase Function: Hexokinase acts on glucose, converting it into glucose-6-phosphate (an initial step in glycolysis).

Citric Acid Cycle (Krebs Cycle)

  • The citric acid cycle is a central metabolic pathway that generates ATP, NADH, and FADH_2 as part of aerobic respiration.

Role of Macronutrients in Metabolism

  • Carbohydrates: Serve as a crucial source of glucose, vital for overall metabolism.
  • Proteins: Provide amino acids, which can be used for protein synthesis or energy production.
  • Fats: Provide free fatty acids and glycerol, important for energy and other metabolic processes.

Glucose and Lipid Metabolism Pathways

  • Gluconeogenesis: The process of synthesizing glucose from non-carbohydrate precursors, such as amino acids or free fatty acids.
  • Lipogenesis: The process by which excess glucose is converted into fat for storage.

Organ-Specific Energy Metabolism

  • Brain:
    • Primarily uses glucose for energy production.
    • Can also utilize ketone bodies as an alternative energy source during prolonged fasting or carbohydrate restriction.
  • Muscle:
    • Utilizes stored glycogen for energy.
    • Breaks down fatty acids for energy.
    • Can break down its own proteins into amino acids, especially during prolonged stress or fasting.
  • Liver:
    • Converts stored glycogen into glucose (glycogenolysis).
    • Converts glycogen into pyruvate.
    • Converts free fatty acids into ketone bodies, particularly during periods of low glucose availability, which can then be used by other tissues like the brain and muscles for energy.