Unit 5: Energy, Exercise and Coordination
Topics 7 and 8
TOPIC 7: RUN FOR YOUR LIFE
5.7.1 - Recall the way in which muscles, tendons, the skeleton and ligaments interact to enable movement including antagonistic muscle pairs, extensors and flexors. Cartilage: a tissue made from collagen, which protects bone ends A muscle: an organ that produces movement by contraction A joint: the junction between two bones A tendon: joins muscle to bone A ligament: joins bone to bone to stabilise a joint
Muscles work in pairs. One muscle produces the opposite movement from the other muscle, therefore, the pairs are called antagonistic pairs. Muscles which cause a joint to extend are called extensors, muscles which cause a limb to retract are called flexors.
A Synovial Joint
5.7.2 - Explain the contraction of skeletal muscle in terms of the sliding filament theory (including the role of actin, myosin, troponin, tropomyosin, Ca2+, ATP). Muscles are made from muscle fibres arranged into bundles. Each fibre is made from bundles of myofibrils, which are extremely long, cylindrical muscle cells.
A RRANGEMENT OF MYOFIBRILS INTO A MUSCLE FIBRE
M USCLE CELLS (M YOFIBRILS )
M USCLE F IBRE
The functional unit of contraction is the sarcomere. Muscle cells contain many sarcomeres arranged in parallel. The muscle cell takes on a characteristic banded appearance because of the regular arrangement of the sarcomeres. This is called striation.
A sacromere. Note the appearance of the muscle
The sarcomere contains overlapping actin and myosin. The myosin is often called the thick filament because the myosin heads make it appear thick. The actin is, therefore, the thin filament The process by which the thin filaments are pulled in towards each other by the myosin is called cross-bridge cycling. It is how muscles contract. 3
1. A nerve impulse arrives at the neuromuscular junction. 2. The muscle cell is depolarised. 3. Ca2+ is released from the sarcoplasmic reticulum inside muscle cells. 4. Ca2+ bids to Troponin protein in the thin filament. 5. Troponin protein and Tropomyosin protein move position in the thin filament. 6. Myosin binding sites are exposed on the thin filament. 7. Myosin heads of the thick filament stick to actin. 8. ATP (already bound to the myosin head) is hydrolysed causing the myosin head to pivot forwards in the powerstroke. 9. As the head pivots the thick filament moves across the thin filament – muscle contraction occurs. 10. ADP diffuses away from the myosin head leaving the ATP-binding site empty. 11. New ATP binds & the myosin head & causes the myosin head to detach from the actin. 12. The myosin head re-cocks.
Key Point: ATP is required to release myosin from actin. If ATP levels drop (assuming Ca2+ is present) the myosin stays attached to the actin and the muscle stays permanently contracted. This is what causes rigor mortis 4
13. The head rebinds further up the myosin. 14. Repeat stages 7 to 13 until the [Ca2+] falls too low, when contraction stops.
5.7.3 - Explain how phosphorylation of ATP requires energy and how dephosphorylation of ATP provides an immediate supply of energy for biological processes Adenosine TriPhosphate (ATP) is made from three components; Ribose (the same sugar that forms the basis of DNA). A base (a group consisting of linked rings of carbon and nitrogen atoms); in this case the base is adenine. Up to 3 phosphate groups. These phosphates are the key to the activity of ATP
The energy used in all cellular reactions comes from ATP. By breaking the 3 rd phosphate from the ATP molecule energy is released, which can be used to power intracellular reactions. The ATP is then regenerated by recombining the phosphate and ADP in respiration (or another process e.g. photosynthesis). The recycling of ATP is crucial for life. For example a runner uses ~84kg of ATP in a marathon (more than their total...