Question

question 1 - 1 point
the common amino acids can be categorized as positively charged, uncharged, or negatively charged based on their charge under physiological conditions. what do all of the negatively charged amino acids have in common?
select the correct answer below:
their side chains (r - group) contain an amino group.
their side chains (r - group) are aromatic.
their side chains (r - group) contain a carboxyl group.
their side chains (r - group) contain a metal.

Explanation:

Negatively charged amino acids (e.g., aspartic acid and glutamic acid) have carboxyl groups (\(-COOH\)) in their side chains. Under physiological conditions (\(pH\approx7.4\)), the carboxyl group can donate a proton (\(H^{+}\)) and become negatively charged (\(-COO^{-}\)). Amino groups (\(-NH_{2}\)) in side chains would make amino acids positively charged (when protonated as \(-NH_{3}^{+}\)). Aromatic side chains (e.g., in phenylalanine, tyrosine) do not confer a negative charge. And common amino acids do not have metals in their side chains.

Answer:

Their side chains (R - group) contain a carboxyl group.