The venoms of poisonous snakes contain (among other things) a class of enzymes known as phospholipases, enzymes that cause the breakdown of phospholipids

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#Section 3: Genetics, Cellular and Molecular Biology

Vertebrate skeletal muscle contraction, also depends on set of specialized accessory proteins that are closely associated with the actin thin filaments:

a) Tropomyosin

b) Troponin

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#Section 3: Genetics, Cellular and Molecular Biology

Muscle contraction depends on two processes that consume enormous amounts of ATP: 

1. Filament sliding, driven by the ATPase of the myosin

2. Ca2+ pumping, driven by the Ca2+ ATPase

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#Section 3: Genetics, Cellular and Molecular Biology

The increase in Ca2+ concentration is transient because the Ca2+ is rapidly pumped back into the SR by an abundant, Ca2+ ATPase.

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#Section 3: Genetics, Cellular and Molecular Biology

AP activates a  voltage gated Ca2+ channel in the T-tubule membrane, it triggers the opening of a Ca2+ -release channel in the closely associated SR membrane

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#Section 3: Genetics, Cellular and Molecular Biology

The arrival of a nerve impulse at a neuromuscular junction triggers an action potential in sarcolemma.

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#Section 3: Genetics, Cellular and Molecular Biology

In skeletal muscle cells, 

a low cytosolic Ca+2 level is maintained by a unique Ca+2 ATPase that continually pumps Ca+2 ions from

the cytosol containing the myofibrils into the SR, establishes a reservoir of Ca+2 in the SR.