Biological Systems MCAT Practice Exam

Acetylcholinesterase is an enzyme that plays a critical role in muscle contraction by hydrolyzing acetylcholine, a neurotransmitter released at the neuromuscular junction. During muscle contraction, acetylcholine binds to its receptors on the muscle cell membrane, triggering a cascade of events that leads to muscle contraction. However, to ensure that this contraction is not perpetuated indefinitely and to allow the muscle to relax, acetylcholine must be removed from the receptor sites. Acetylcholinesterase acts by breaking down acetylcholine into acetate and choline. This hydrolysis effectively terminates the signaling process initiated by acetylcholine, allowing the muscle to relax and preventing continuous stimulation of muscle contraction. By controlling the concentration of acetylcholine in the synaptic cleft, acetylcholinesterase ensures that each muscle contraction is short-lived and allows for controlled, repeated contractions as required. The other roles mentioned are not functions of acetylcholinesterase. While muscle contraction is initiated by the action of acetylcholine, it does not stimulate contraction directly. Calcium reuptake and neurotransmitter release, while important processes in muscle physiology, are managed by different mechanisms and proteins, not by acetylcholinesterase.