Human Cells Energy systems in muscle cells Higher Human Biology Human Cells Energy systems in muscle cells

What do you know? What do muscle cells do? What do they need to do this? Do all activities put the same demand on muscle cells? What happens if muscle cells cannot be provided with enough oxygen?

What you will be learning About the creatine phosphate system fro providing energy with ATP More on lactic acid metabolism About slow and fast twitch muscle fibres and how they work

Creatine phosphate system ATP is the source of immediate energy for cells. In intense activity ATP is quickly broken down to ADP and Pi releasing energy ( a few contractions). As strenuous activity continues creatine phosphate in muscle cells breaks down releasing phosphate and energy. This energy converts the ADP and Pi back to ATP. The ATP is used to sustain maximum muscular contractions for approximately 10 seconds The creatine phosphate quickly runs out. This system supports activities like a fast sprint and lifting and lowering a heavy weight.

Creatine phosphate system At rest when little ATP is being used creatine phosphate can be regenerated. Enzymes breakdown ATP to release phosphate and energy. These can be used to produce creatine phosphate by a process of phosphorylation. The creatine phosphate ia a high energy reserve for muscles during intense strenuous activity.

Lactic Acid Metabolism During glycolysis 2ATP, 2NADH and pyruvate are produced. If oxygen is present pyruvate will continue into the citric acid cycle and the process will be completed in the hydrogen transport system. This is aerobic respiration When oxygen is scare then neither the citric acid cycle or hydrogen transport system will operate. Instead the cells rely on the 2ATP for energy from glycolysis.

Lactic Acid Metabolism The hydrogen from NADH is used to convert pyruvate to lactic acid (lactate). The NAD is used again in glycolysis to transport further H+ ions. This is fermentation. Lactic acid builds up in muscle cells causing fatigue and an oxygen debt develops. The oxygen debt is repaid when exercise stops. The lactic acid is transported to the liver and is changed back to pyruvate and glucose.

Types of skeletal muscle fibres Skeletal muscle fibres bring about movement, this requires energy. 2 types of skeletal muscle fibre exist based on their twitch rate: Type 1 - Slow twitch muscle fibres Type 2 – Fast twitch muscle fibres

Slow and Fast twitch muscle fibres Slow twitch fibres depend on aerobic respiration to supply their ATP and are put to use in endurance activities like long distance running, cycling and rowing. Fast twitch fibres depend on glycolysis to supply their ATP and are put to use in power activities like weight lifting and sprinting Myoglobin in muscle cells helps extract oxygen from blood with its high affinity for oxygen. Most skeletal muscles have a mix of slow and fast twitch fibres. Athletes will often show different % of fibre types depending on their sporting activities.

Slow and Fast twitch compared Feature Type of skeletal muscle fibre 1 (slow – twitch) 2 (fast – twitch) Speed of contraction slow fast Contraction length long short Speed of fatigue Usual source of ATP Glycolysis and aerobic Glycolysis only Mitochondria number large small Blood capillary density high low Myoglobin concentration Major fuel stores used fats Glycogen and creatine phosphate

What have you learned? What happens to creatine phosphate in muscle cells? Why does this happen? Approximately how much strenuous activity is supported by ATP and creatine phosphate? Why is lactic acid produced in muscle cells? Which part of the respiration cycle produces lactic acid? What happens in lactic acid metabolism? Where is the lactic acid processed? What are the 2 types of skeletal muscle fibres? What are the differences between the 2 types of muscle fibre?

NAR preparation 3 Summary sheets for all 8 chapters Textbook pages 118 to 123 Questions 1, 3, 4, 5, 6, 7, 8, 9 NAR Tuesday 1st November