Metabolic Reactions That Produce ATP in Muscle Fibers

Creatine Phosphate System (Phosphagen System)

muscle fibers store creatine phosphate (CP), a high-energy molecule

How does the Creatine Phosphate System work

• when contraction begins, CP transfers its phosphate to ADP → makes ATP

• enzyme involved: creatine kinase

Characteristics of Creatine Phosphate System

• fastest way to make ATP

• anaerobic (no oxygen needed)

• provides enough energy for about 15 seconds of activity

  • ex: sprinting, weightlifting

Anaerobic glycolysis (Glycolysis → lactic acid)

glucose from blood or glycogen is broken down into pyruvic acid, generating 2 ATP per glucose

When oxygen is low

pyruvic acid is converted into lactic acid, which diffuses into blood

Characteristics of anaerobic glycolysis

• no oxygen required

• produces ATP quickly

• supplies energy for 30-40 seconds of muscle activity

• useful for 400-m sprint, intense exercise

Aerobic Cellular Respiration

a long series of oxygen-requiring reactions in the mitochondria

Fuel sources for Aerobic Cellular Respiration

• pyruvic acid (from glycolysis)

• Fatty acids

• Amino acids

• Oxygen from blood hemoglobin and myoglobin in muscle

Characteristics of Aerobic Cellular Respiration

• Requires oxygen

• Slowest but most efficient ATP production

• Supports prolonged activity (minutes to hours)

  • example: jogging, distance swimming