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Nine of the twenty amino acids are called essential in humans because they:
AAre needed in far larger daily amounts than others
BAre the only ones that appear in enzyme active sites
CCannot be produced by the body and come from diet
DCannot be linked into polypeptides without a cofactor
Answer & Solution
Correct answer: C. Cannot be produced by the body and come from diet
1. Every one of the twenty amino acids is required to build proteins, so need alone cannot be the criterion.
2. The distinction is whether the body can synthesise the amino acid itself.
3. Nine are considered essential because the human body cannot produce them.
4. They must therefore be obtained from the diet.
5. Options A, B and D describe properties that do not track the essential and non-essential split.
_Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 3 'Biological Macromolecules', sections 3.1-3.5_
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