Triplet contains one complete 13-protofilament microtubule (A tubule) and two additional tubules (B & C tubule) consisting of 10 protofilaments each.

TLS Online TPP Program

#Id: 8390

#Unit 2. Cellular Organization

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

TLS Online TPP Program

#Id: 8391

#Unit 2. Cellular Organization

When the Ca2+ level rises, Ca2+ binds CaM.

TLS Online TPP Program

#Id: 8392

#Unit 2. Cellular Organization

The CaM*-Ca2+ complex binds and activates MLC kinase, phosphorylates the myosin LC. 

TLS Online TPP Program

#Id: 8393

#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

#Id: 8395

#Unit 2. Cellular Organization

Sarcomere

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