Biology 105
Biology of Exercise
Spring 2003

2/14/03 - Post-class outline

Learning objectives:

• How are foods converted into useable energy?
• How is the level of glucose in the body regulated?

Diagrams.

• Overview of carbohydrate digestion, absorption, and metabolism
• Insulin and glucagon actions
• Anaerobic and aerobic metabolism during sustained exercise
• Glycemic index table (external, from Gatorade Sports Science Institute paper) (choose pdf to print)
• GI exercise

Insulin and glucagon are part of a hormonal control system that regulates blood glucose.

• The hormone insulin is released from the pancreas in response to increased blood glucose.
• It triggers increased uptake of glucose into cells, increased breakdown of glucose to form ATP and increased synthesis of glucose into the storage molecule glycogen.
• Glucagon is a hormone released by the pancreas when blood glucose is low. It triggers opposite effects to insulin.

Sources of ATP during exercise

• Phosphagen
  • Some ATP is present in the cell and can be used to power muscle contraction
  • Phosphocreatine (P-Cr) can be used to quickly synthesize more ATP.
    • P-Cr + ADP = Cr + ATP
  • The phosphagen system can provide ATP at a very rapid rate, but only for a few seconds (up to 15).
  • It is used at the start of exercise and during very short, intense exercise efforts.
• Anaerobic metabolism
  • glucose (6C) + 2ADP + 2Pi = 2ATP + 2 lactic acid (3C) + heat
  • Can occur in the absence of oxygen
  • Is inefficient in use of glucose (1 glucose yields 2 ATP).
  • Can produce ATP relatively rapidly.
  • Lactic acid is a by-product. Lactic acid has negative effects on cell function.
  • Anaerobic metabolism can produce relatively high power but with low endurance.
• Aerobic metabolism
  • glucose (6C) + oxygen + 36ADP + 36Pi = 36ATP + 6CO2 (1C) + heat + water
    • glycolysis is breakdown of glucose to pyruvate
    • the citric acid cycle (or Krebs cycle or TCA cycle) converts acetyl CoA to high energy intermediates (i.e. NADPH)
    • the electron transport chain converts NADPH into ATP.
  • Efficient in glucose use (36 ATP per glucose)
  • No production of metabolic wastes
  • Slower than anaerobic (more steps than anaerobic)
  • Can produce lower power, but has much higher endurance than anaerobic.