Problem
Skeletal muscle contraction is a complex process involving actin and myosin filaments, along with a number of assisting proteins and cellular structures.
i. In a relaxed state, why is there a large gap between the ends of myosin filaments and the z-disk (the z-disk is where actin filaments branch off at the ends of sarcomeres)? Where does this space go during muscle contraction?
ii. Why is it important for the sarcoplasmic reticulum & T-tubules to exist in a mesh that surrounds the myofibrils in muscle cells? If the sarcoplasmic reticulum existed in a conformation that resembled the nucleus - i.e. Calcium ions are stored in one condensed location in each muscle cell - how would that affect the speed of muscle contraction?
iii. Actin filaments are accompanied by tropomyosin and troponin protein complexes. What role do both of these protein complexes have in regulating muscle contraction in response to cellular signals?