1. After death, the muscles of the body become very stiff and inextensible. This

Question

1. After death, the muscles of the body become very stiff and inextensible. This phenomenon is referred to as rigor mortis, and the muscles are said to be in a state of rigor.



(a) Explain the biochemical basis of rigor mortis, in terms of the interaction of actin and myosin; ie, where in the contraction cycle is the muscle arrested? (Describe the two roles played by ATP in this phenomenon [the second role of ATP relates to Ca++].)







































(b) Would your muscles be likely to go into rigor faster if you were to die while racing to class, or while sitting in lecture? Explain.

Explanation / Answer

It has to do with binding and ATP. In the sliding filament model of contraction, the myosin heads bind the actin filament and pull it along. When the cycle is complete, a fresh molecule of ATP must bind in order to reset the system. Without that fresh ATP, the myosin remains locked to the actin, in a "pulled" position, and the muscles become stiff. Within a day or so, the filaments themselves begin to break down and decompose, releasing the muscles. If you were to die while exerting yourself, more you would have less ATP in your cells, so rigor would set in faster.

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