Striated muscles contain repeating sarcomeres of overlapping arrays of long, thin actin and thicker myosin filaments. Myosin filaments contains the myosin heads, which are enzymes that can bind to actin, split and make use of the energy from ATP. When muscle contraction starts, myosin heads bind to actin, change their configuration on actin, liberating the products of ATP hydrolysis and causing slide of the actin and myosin filaments. The action of the proteins troponin and tropomyosin on the actin filaments regulates vertebrae striated muscle contraction. The release of calcium ions from the sarcoplasmic reticulum is triggered by the nervous stimulation which causes depolarization of muscle membrane. Calcium ions bind to troponin and thus cause or allow the tropomyosin strands on the actin filament to move so that the part of the actin surface where myosin heads need to bind is uncovered. Contraction then occurs and only stops when the sarcoplasmic reticulum pumps calcium out of the muscle interior.
So basically, what triggers the uncovering of the myosin binding site on actin is the calcium ions binding to troponin and changing configuration.
The nuclear envelope is perforated with pores to allow it to move in and out of the nucleus.
Every cell in the body has a nucleus, except for mature erythrocytes (red blood cells). While some cells contain more than one nucleus such as skeletal muscle and some other cells contain several nuclei.
The nuclear envelope surrounds the nucleus. i. e. largest organelle of the cell. It has a similar structure to that of
the plasma membrane. But the nuclear envelope contains tiny pores that allow a few substances to pass between it and outside the cytoplasm, i.e. the cell contents excluding the nucleus.
Therefore, the nuclear envelope is perforated with pores to allow it to move in and out of the nucleus.
To know more about the nucleus, refer to the below link:
brainly.com/question/2437355
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Answer:
The amount of mass that planet Jupiter has in the solar system makes it approximately five times larger than all other planets in it. As Jupiter’s gravity pulled on another planet tightly, its diameter grew and it expanded. The density and gravity continued to increase, resulting in even more planet compression.
Explanation:
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