Cohesins are composed of four subunits: 

Smc1, Smc3, Scc1, and Scc3

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The length of the myosin II neck domain determines the rate of movement.

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#Unit 2. Cellular Organization

In the absence of ATP, the myosin head is firmly attached to the actin filament. 

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In the presence of ATP,  myosin head releases from the actin filament. 

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Thick-filament regulation

Myosin-dependent mechanism regulate contraction in smooth muscle and non-muscle cells.

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In vertebrate smooth muscle, phosphorylation of the myosin regulatory light chain activates contraction in Ca2+ dependent manner.

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When the Ca2+ levels drop:

Myosin LC is dephosphorylated by MLC phosphatase, causing muscle relaxation.