MCAT Biological and Biochemical Foundations of Living Systems Practice Exam

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Question: 1 / 20

What amino acid serves as the precursor to serotonin?

Tyrosine

Phenylalanine

Tryptophan

The correct answer is tryptophan because it is the amino acid that serves as the direct precursor to serotonin. In the body, tryptophan undergoes a series of enzymatic transformations to ultimately produce serotonin, a neurotransmitter that plays critical roles in mood regulation and other physiological functions.

The process begins with tryptophan being hydroxylated by the enzyme tryptophan hydroxylase to form 5-hydroxytryptophan (5-HTP). This intermediate is then decarboxylated by the enzyme aromatic L-amino acid decarboxylase, resulting in the production of serotonin, also known as 5-hydroxytryptamine (5-HT).

Understanding this biochemical pathway highlights the significance of tryptophan not just as a constituent of proteins but also as a crucial player in neurotransmitter synthesis. Thus, tryptophan’s role in forming serotonin makes it the key amino acid in this context.

Glutamate

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