Question

In which of the following pairs of amino acids does an excess of the first amino acid decrease the need for the second?

a. leucine, lysine
b. methylhistidine, histidine
c. tyrosine, phenylalanine
d. glycine, arginine

Answer 1

An excess of phenylalanine can decrease the need for tyrosine because tyrosine can be synthesized from phenylalanine by the enzyme phenylalanine hydroxylase.

Step-by-step explanation:

The question asks about the relationship between amino acids and how an excess of one amino acid can decrease the need for another. From the options provided, tyrosine and phenylalanine have a precursor-product relationship where the presence of phenylalanine can be reduced to produce tyrosine. This means that an excess of phenylalanine can decrease the body's need for tyrosine, as phenylalanine can be converted into tyrosine by the enzyme phenylalanine hydroxylase. Therefore, the correct pair from the given options where an excess of the first decreases the need for the second is c. tyrosine, phenylalanine.