Answer:
When a muscle cell contracts, the myosin heads each produce a single power stroke.
Explanation:
In rest, attraction strengths between myosin and actin filaments are inhibited by the tropomyosin. When the muscle fiber membrane depolarizes, the action potential caused by this depolarization enters the t-tubules depolarizing the inner portion of the muscle fiber. This activates calcium channels in the T tubules membrane and releases calcium into the sarcolemma. At this point, <em>tropomyosin is obstructing binding sites for myosin on the thin filament</em>. When calcium binds to the troponin C, the troponin T alters the tropomyosin by moving it and then unblocks the binding sites. Myosin heads bind to the uncovered actin-binding sites forming cross-bridges, and while doing it ATP is transformed into ADP and inorganic phosphate which is liberated. Myofilaments slide impulsed by chemical energy collected in myosin heads, <u>producing a power stroke</u>. The power stroke initiates when the myosin cross-bridge binds to actin. As they slide, ADP molecules are released. A new ATP links to myosin heads and breaks the bindings to the actin filament. Then ATP splits into ADP and phosphate, and the energy produced is accumulated in the myosin heads, which starts a new binding cycle to actin. Z-bands are then pulled toward each other, thus shortening the sarcomere and the I-band, and producing muscle fiber contraction.
This has to do with SURFACE TO VOLUME RATIO. For a typical small cell, its surface area to the volume ratio get smaller as the cell grows. This implies that, if the cell grows beyond a certain limit, then the amount of nutrients that entered the cell will be limited, that is , nutrients will not be able to migrate into the cell as needed. To avoid this, the cell has to divide to reduce its surface to volume ratio.<span />
Systematic error affects the
measurement in a constant way and represents stable factors that affect the
observed score in the same way each time the measurement is made. Systematic
error is a steady, repeatable error joined with faulty measuring equipment or an
imperfect experiment design.
The answer is 60%
Biomes are regions which have similar climate as well as the vegetation. Many people have defined the biomes on different basis some based on temperature , some on vegetation and many others.Some major terrestrial biomes include tropical forests, savannas, deserts, tundra, temperate deciduous forests etc
