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Energy Systems in Muscle Cells Higher Human Biology Unit 1 – Section 8 Learning Intentions By the end of this section you should be able to: I can explain how creatine phosphate can break down, releasing phosphate and allowing the production of ATP from ADP and phosphate during strenuous activity. I can describe the conversion of pyruvate to lactic acid during strenuous activity when insufficient oxygen is available, and the build-up of an oxygen debt, which must be repaid when the activity is over. I can identify the two types of muscle fibre, and the differences in their number of mitochondria, blood supply, storage fuel and rate of contraction and give examples of the type of activities which depend on them. Creatine Phosphate System • During intense muscular activity, muscle cells use ATP as a source of energy. • However, each muscle cell only contains enough ATP for a few contractions. • Most of the energy needed for repetitive muscular contraction comes from a chemical called creatine phosphate. During Strenuous Activity Creatine Phosphate ATP Phosphate Creatine ADP The breakdown of the creatine phosphate releases the phosphate which can then convert ADP into ATP by phosphorylation. This ATP can then be used for muscular contraction for About ten seconds Sufficient energy is generated for short bursts of exercise e.g. 100m sprint During Rest Period ADP Creatine Phosphate Creatine Phosphate ATP When the demand for energy is low during rest, little ATP is required. Therefore any ATP is broken down to release energy and phosphate to regenerate creatine phosphate (acts as a high energy reserve). This is an enzyme controlled pathway. Lactic Acid Metabolism • During strenuous activity, ATP only lasts seconds. ATP can be replenished by the breakdown of creatine phosphate until it is used up. • Cells will then start to respire anaerobically (by fermentation) as the cells will not be receiving an adequate supply of oxygen • Oxygen is needed for the citric cycle and the electron transport chain. Without the oxygen these stages do not occur Lactic Acid Metabolism • Only glycolysis produces ATP (2 instead of 38) • The pyruvate is converted into lactic acid (lactate) • Lactic acid can build up and cause fatigue and an oxygen debt builds up • This process is reversible when at rest and more oxygen becomes available. • The lactic acid is transported to the liver to be converted back to pyruvic acid. Skeletal Muscle Fibres • Physical activity requires parts of the body to move and is brought about by skeletal muscle fibres (either slow-twitch or fast-twitch). • Skeletal muscles contain a genetically determined mixture of slow-twitch and fasttwitch fibres. In most muscles the ratio is balanced. • However in other muscles one will dominate For example the back contains mainly slow-twitch muscles and the eyes mainly fast-twitch muscles Myoglobin • Muscles cells contain an oxygen storing protein called MYOGLOBIN. • It has a higher affinity for oxygen than haemoglobin so can extract oxygen from the blood to be used by the muscle cells(especially those in slow twitch Slow-twitch fibres rely on aerobic respiration Fast-twitch muscle fibres depend on to generate most of the ATP and are effective glycolysis to generate ATP for power during endurance exercise such as rowing and events such as sprinting cycling.