The process of muscle contraction requires several steps.
The most famous theory on how the contraction and relaxation of muscles take place is the sliding filament theory.
However, this theory has been refined and one important addition to it is the mechanism by which myosin can pull actin and cause shortening of the sarcomere.
For the movement of myosin, it binds and releases actin and forms cross bridges.
Myosin is subdivided into two regions - S1 and S2. The contraction of the S1 region is what constitutes the power stroke.
An important requirement of the power stroke is the hydrolysis of ATP to release an inorganic phosphate which provides energy for the process.
How many chromosomes would be present in a cell after anaphase of Mitosis? During anaphase, sister chromatids separate to opposite sides of the cell. Therefore the 4n after doubling returns to 2n at each end of the dividing cell after anaphase. But until cytokinesis (1 cell pinching into 2), it's still one cell therefore 4n = 28
