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, wherein the contraction cycle is the muscle arrested

Rigor mortis is the state of muscle to get stiff after few hours of death due to cessation of breathing and cessation of the heartbeat.

The muscle contraction occurs due to the generation of electric potential across the membrane which pumps calcium ions when receives the signal from neuron. These ion interact with muscle protein actin and myosin in the presence of adenosine triphosphate (ATP).

When a person die, its breathing and blood circulation stops and body undegoes anaerobic respiration and unable to produce efficient ATP. Due to unavailability of oxygen the myosin and actin filaments remain rigid and not able to release from the contracted state and the calcium ions unable to move out of the muscles.

Hence, the rigor mortis remain in arrested due to absence of ATP.