Which of the following amino acids has a negatively charged side chain at physiological pH?Group of answer choicesglutamineasparaginelysinemethionineglutamic acidarginine

The amino acid that has a negatively charged side chain at physiological pH is glutamic acid.

Here's why:

Amino acids are organic compounds composed of amine (-NH2) and carboxyl (-COOH) functional groups, along with a side chain (R group) specific to each amino acid. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen, though other elements are found in the side chains of certain amino acids.

At physiological pH (around 7.4), the carboxyl group (-COOH) can lose a proton (H+) to become negatively charged (-COO-). This is known as deprotonation.

Among the options given, glutamic acid has a side chain that can be deprotonated at physiological pH, resulting in a negative charge. The side chain of glutamic acid is -CH2CH2COOH, and the -COOH part can lose a proton to become -COO-.

The other amino acids listed either have neutral side chains (glutamine, asparagine, methionine) or positively charged side chains (lysine, arginine) at physiological pH.