Energy sources - types
• The amount of ATP stored in a skeletal muscle cell can only provide muscular activity for two to three seconds. • Muscle cells must be able to generate additional molecules of ATP to continue contracting. • Muscle cells can generate ATP from several processes: • Phosphogen system • Anaerobic cellular respiration • Aerobic cellular respiration • The duration of muscular activity determines which energy process is used. Energy sources - creatine phosphate • Through a direct phosphorylation reaction unique to muscle cells, ATP molecules are rapidly generated from creatine phosphate and ADP. • One creatine phosphate molecule generates one ATP molecule. • The phosphogen system can sustain maximum muscle contraction for about 15 seconds. • When the muscle is inactive, creatine is restored to creatine phosphate. Energy sources - anaerobic cellular respiration • Muscle cells use glucose as an source during longer periods of activity. • Glucose can be supplied to muscle cells by the breakdown of glycogen. • Glycolysis: Glucose is broken down into pyruvic acid. • One glucose molecule can yield a net gain of two ATP molecules. • The pyruvic acid is commonly oxidized to generate large amounts Of ATP in the mitochondria during aerobic respiration. • When there is a lack of oxygen in the muscle, pyruvic acid is converted to lactic acid. Energy sources - anaerobic cellular respiration • Anaerobic cellular respiration Can produce enough ATP to sustain maximum muscle activity for 30-40 seconds. Energy sources - aerobic cellular respiration • Extended muscle activity requires a continuous supply of ATP. • A series of reactions known as aerobic cellular respiration utilizes oxygen and available nutrients to produce large amounts of ATP. • Nutrient sources include: • Carbohydrates (pyruvic acid) • Proteins (amino acids) • Lipids (fatty acids) • One glucose molecule can generate a net yield of thirty-six ATP molecules. • Aerobic cellular respiration is able to produce enough ATP to sustain maximum muscular activity for minutes and hours.
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