Question

Figure 16.6 The deadly nerve gas Sarin irreversibly inhibits acetycholinesterase. What effect would Sarin have on muscle contraction?

Short answer

Answer: The effect of sarin on muscle contraction is that it causes constant, uncontrolled muscle contraction due to the inhibition of acetycholinesterase. Sarin binds to the active site of acetycholinesterase, preventing the enzyme from breaking down acetylcholine, which leads to an accumulation of the neurotransmitter in the synaptic cleft. This results in continuous stimulation of the muscle cell, causing muscle spasms, paralysis, and eventually death.

Step-by-step solution

Understand the neuromuscular junction process

The neuromuscular junction is the site of communication between a motor neuron and a muscle cell. To initiate muscle contraction, the motor neuron releases the neurotransmitter acetylcholine (ACh) from its axon terminal. The ACh molecules diffuse across the synaptic cleft and bind to ACh receptors on the sarcolemma (muscle cell membrane), causing a depolarization and signaling the muscle cell to contract.

Identify the role of acetycholinesterase in muscle contraction

Acetycholinesterase is an enzyme present in the synaptic cleft. Its main function is to break down ACh molecules after they have transmitted the signal to the muscle cell. This breakdown of ACh allows the muscle cell to return to its resting state, making it ready for the next signal to contract.

Understand the effect of sarin on acetycholinesterase

Sarin is a powerful inhibitor of acetycholinesterase. When sarin enters the synaptic cleft, it binds to the active site of acetycholinesterase, preventing the enzyme from breaking down ACh molecules. This inhibition of acetycholinesterase is irreversible, meaning that the enzyme cannot regain its function.

Determine the effect of sarin on muscle contraction

Since sarin inhibits acetycholinesterase and the enzyme cannot break down ACh, the neurotransmitter accumulates in the synaptic cleft. This abundance of ACh causes continuous stimulation of the muscle cell, leading to constant depolarization and muscle contraction. The constant, uncontrolled muscle contraction can result in muscle spasms, paralysis, and eventually, death.