When the muscle cell (fiber) level. First, not only examining a myofibril, one of the first obser- do muscles vary in size, they can also vary vations that can be made is that the cylindri- in the number of cells. For example, the cal organelle is made up of repeating units. muscle that is responsible for adjusting the These repeating units are known as sarco- tension of the eardrum (tensor tympani) meres. Contained in each sarcomere are all has only a few hundred muscle cells, while the structural elements needed to perform the the medial gastrocnemius (used in humans physical act of contraction at the molecular for walking) has over a million muscle cells level. Current proteomic analysis estimates (Feinstein et al. 1955). Not only does the that over 65 proteins make up the structure number of cells influence muscle function of the sarcomere (Fraterman et al. 2007).
4 vesicle formation ; 5 movement of vesicles ; 6 exocytosis / vesicles fuse with membrane ; 2+ 7 ref. active transport (of ACh / Ca ) ; 8 AVP ; e.g. ref to microtubules / endocytosis 4 max muscular contraction 9 ATP attaches to myosin head / ATPase ; 10 hydrolysis of ATP / ATP → ADP + P ; 11 myosin head tilts / shortening of sarcomere ; 12 ATP / energy, required for detachment of myosin head ; 13 from actin ; 14 calcium pumps in sarcoplasmic reticulum ; 15 synthesis of protein (for repair, growth) ; 16 AVP ; 5 max 8 max QWC – clear, well-organised using specialist terms ; 1 award the QWC mark if four of the following are used in correct context
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