N3

Anatomy & Physiology II: Carbohydrate Metabolism

Metabolism: Fundamental Concepts

  • Metabolism: All chemical processes within the body.
    • Catabolism: Process of breaking down complex structures into simpler ones.
    • Involves Hydrolysis: The addition of water to break bonds.
    • Anabolism: Building complex structures from simpler ones.
    • Involves Dehydration Synthesis: Removal of water to make bonds.

Use of Nutrients for Energy

  • Cells utilize carbohydrates, lipids, and proteins to produce energy.
  • Nutrients are broken down, absorbed, and metabolized in mitochondria to produce ATP (Adenosine Triphosphate).

Adenosine Triphosphate (ATP)

  • Structure of ATP:
    • Composed of Adenosine (adenine and ribose) and a triphosphate chain (three phosphate groups).
    • High-energy bonds exist between phosphate groups: the bond between the second (beta) and third (gamma) phosphate stores the most energy.
  • Energy Release:
    • Removing the gamma phosphate releases significant energy, converting ATP to ADP (Adenosine Diphosphate).
    • Further removal of the second phosphate (beta) yields AMP (Adenosine Monophosphate).
    • ATP can be regenerated through reattachment of phosphate groups to ADP or AMP, which requires energy.

Energy Dynamics

  • Energy: The capacity to do work, measurable in calories.
  • The energy in food is found within the chemical bonds of molecules.
  • Energy is released when these bonds break during metabolism.

Coenzymes in Metabolism

  • Coenzymes facilitate redox reactions (oxidation-reduction) and are derived from B vitamins:
    • Nicotinamide adenine dinucleotide (NAD⁺): Accepts electrons, becoming NADH.
    • Chemical reaction: (NAD^+ + 2H + 2e^-
      ightarrow NADH + H^+).
    • Flavin adenine dinucleotide (FAD): Accepts lower-energy electrons than NAD⁺, reduced to FADH₂.
    • Chemical reaction: (FAD + 2H + 2e^-
      ightarrow FADH_2).

Phosphorylation

  • Phosphorylation: The addition of a phosphate group to a molecule, requiring energy to form the bond.
  • Dephosphorylation: The removal of a phosphate group, releasing energy when the bond breaks.
    • Phosphorylated molecules are activated for cellular functions.

Phosphorylation Processes

  • Substrate-Level Phosphorylation:
    • Direct transfer of high-energy phosphate groups from phosphorylated substances to ADP to produce ATP.
    • Occurs anaerobically, specifically: 2 times during glycolysis (in the cytosol) and 1 time in the citric acid cycle.
  • Oxidative Phosphorylation:
    • Produces more ATP than substrate-level phosphorylation, only occurring in aerobic conditions.
    • Energy from nutrient oxidation pumps H⁺ across the inner mitochondrial membrane, with backflow through ATP synthase producing ATP from ADP and phosphate.

Overview of Carbohydrate Metabolism

  • Acetyl-CoA: Functions as a coenzyme in biological reactions, formed from the oxidation of carbohydrates, fats, and proteins.
    • Serves as a precursor to the Krebs cycle by combining with oxaloacetate to form citric acid.

Cellular (Aerobic) Respiration: Steps

  • Process Summary:
    • Breaks down glucose into ATP through:
    1. Glycolysis
    2. Transitional Step (Conversion)
    3. Krebs Cycle
    4. Electron Transport Chain (ETC)
  • Overall Reaction: (C6H{12}O6 + 6O2
    ightarrow 6CO2 + 6H2O + Energy).

Glycolysis Details

  • Definition: Breakdown of glucose into 2 pyruvate molecules in the cytosol, yielding 2 ATP and 2 NADH without requiring oxygen.
    • Process: 10 chemical steps, producing two 3-carbon pyruvate from one 6-carbon glucose.

Transitional Phase Details

  • Each pyruvate enters the mitochondrial matrix, forming Acetyl-CoA through decarboxylation (removal of CO₂).
    • Results in 2 NADH production from both pyruvates, with no ATP generated.

Citric Acid Cycle Details

  • Occurs in the mitochondrial matrix, generates 2 ATP, and large amounts of NADH and FADH₂, necessary for the next stage of metabolism.
    • Each cycle contributes NADH, FADH₂, and CO₂ as byproducts while maintaining aerobic conditions.

Electron Transport Chain and Oxidative Phosphorylation

  • Mechanism: ETC located on inner mitochondrial membrane, involves a series of electron carriers transferring electrons and establishing a hydrogen ion (H⁺) gradient.
    • ATP Production:
    • Each NADH yields approximately 3 ATP; each FADH₂ yields approximately 2 ATP, leading to a net production of 32 ATP.

ATP Production Table

  • Summary of ATP Production:
    • Glycolysis: 2 ATP
    • Acetyl-CoA Production: 0 ATP
    • Krebs Cycle: 2 ATP
    • Electron Transport Chain: 28 ATP
    • Total from one Glucose Molecule: 32 ATP

Other Carbohydrate Metabolism Processes

  • Glycogenesis: Formation of glycogen from glucose stimulated by insulin when glucose levels are high.
  • Glycogenolysis: Breakdown of glycogen to glucose when glucose levels are low, stimulated by glucagon.
  • Gluconeogenesis: Formation of glucose from non-carbohydrate sources during fasting or starvation, primarily in the liver.

Summary of Carbohydrate Reactions

  • Glycolysis: Glucose to pyruvate (anaerobic, produces ATP).
  • Glycogenesis: Storage of glucose as glycogen.
  • Glycogenolysis: Release of glucose from glycogen for ATP production.
  • Gluconeogenesis: Generation of glucose from non-carbohydrate sources to stabilize blood sugar levels.

Edits and Acknowledgments

  • Edition date: 7/15/25 - Updates for 4-credit course with checks for accuracy.
  • Contributors include Stephen Taylor, Julie Underwood, Laura Bianco, John Kaminski, and BIO 121 cross college team.