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.