The energy for Na+-K+-2Cl- cotransporter is derived from the low intracellular Na+ gradient, which is maintained by the Na+-K+ ATPase

TLS Online TPP Program

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#Unit 2. Cellular Organization

Phosphorylation of MLC 

unfolds the myosin II, active and can assemble into bipolar filaments for contraction

TLS Online TPP Program

#Id: 8394

#Unit 2. Cellular Organization

When the Ca2+ levels drop:

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

TLS Online TPP Program

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#Unit 2. Cellular Organization

Sarcomere

Within each skeletal muscle cell are many myofibrils consisting of a repeating array of a specialized structure

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#Id: 8396

#Unit 2. Cellular Organization

Each sarcomere contains two major types of filaments: 

Thick filaments (myosin II)

Thin filaments (actin and associated proteins)

TLS Online TPP Program

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#Unit 2. Cellular Organization

Z disk 

Thin actin filaments are assembled with their (+) ends embedded in a densely staining structure

TLS Online TPP Program

#Id: 8398

#Unit 2. Cellular Organization

In the presence of ATP and Ca+2 , the myosin heads extending from the thick

filaments walk toward the (+) ends of the thin filaments.