Bioenergetics Chapter 2

Bioenergetics (Chapter 2)

• Metabolism is the total sum of all chemical reactions in the body, including energy involved in digestion and micro reactions.
• Two main types:
  • Anabolic: synthesis or building of molecules. Examples include insulin's role in building adipose tissue (fat).
  • Catabolic: breakdown of molecules. Example includes bioenergetics, the process converting food (fats, carbohydrates, protein) into usable energy forms at rest or during exercise.
• ATP (adenosine triphosphate)
  • Not a long-term energy store. (~90 g total at rest)
  • Resting intramuscular concentration is 5 mmol/kg.
  • Muscle contraction can increase cellular ATP demand 500-1000x.
• Macronutrients:
  • Proteins: 4 Calories/gram
  • Carbohydrates: 4 Calories/gram
  • Fats: 9 Calories/gram
  • Carbohydrates and fats are the primary energy sources during exercise.
  • Carbohydrates are more important for elite athletes.

ATP Production

• Enzymes are protein molecules that speed up reactions without being consumed.
• Enzymes lower the activation energy required for a reaction.
• The active site is where the enzyme's magic occurs.
• Enzymes can function both anabolically and catabolically.
• Two factors regulating the speed of enzyme activity:
  • pH: Each enzyme has an optimal pH where it functions best.
  • Temperature: High temperatures can denature enzymes.
• Energy systems:
  • Phosphagen (ATP-PCR, Phosphocreatine): The first and shortest system, used during the initial seconds of activity (less than 3 seconds). Free-floating ATP is used.
  • Glycolytic-Lactate: A second system using two types of pathways:
    • Fast Glycolysis (anaerobic): utilized during short, high-intensity activities like plyometrics, weightlifting, or sprinting.
    • Slow Glycolysis (aerobic): used in activities like walking, swimming, or cycling.
  • Oxidative Phosphorylation (Mitochondrial Respiration): The third and most efficient system; used for longer duration exercise.

Anaerobic System

• Phosphagen system: uses phosphocreatine (PCR) to generate ATP, a one-step process involving creatine kinase.
• Anaerobic glycolysis: a two-step process with creatine kinase involved and negative feedback system when ATP levels increase, creatine kinase activity decreases.
• Creatine supplementation increases intramuscular stores of PCR, allowing for quicker energy release.

CHO Metabolism

• Four stages of CHO metabolism:
  • Stage 1: Glycolysis (anaerobic) - breaking down glucose or glycogen into pyruvate to produce ATP. This stage has two phases: energy investment and energy payoff.
  • Stage 2: Conversion of pyruvate to Acetyl-CoA (aerobic) - pyruvate is converted into acetyl-CoA to prepare for the Krebs cycle.
  • Stage 3: Krebs Cycle( Aerobic) - Series of reactions where energy is harvested from Acetyl-CoA. Electron carriers NADH and FADH2 are produced.
  • Stage 4: Electron Transport Chain (ETC) (Aerobic) - Electron carriers (NADH and FADH2) generate ATP via oxidative phosphorylation.

Aerobic Glycolysis

• Conversion of pyruvate to Acetyl CoA in the mitochondrial matrix.
• Pyruvate Dehydrogenase is the enzyme responsible for this reaction.
• The Acetyl-CoA is then used in the Krebs Cycle.

Other Important Points

• Lactate is a byproduct of anaerobic glycolysis.
• Lactate threshold is the point where lactate accumulation increases markedly, indicating a transition from primarily aerobic to anaerobic metabolism.
• Aerobic glycolysis and the Krebs cycle produce ATP through oxidative phosphorylation.
• Respiration quotient (RQ) relates how the body is burning energy.