Final answer:
Glutamic acid has a net negative charge at physiological pH (~7.4) because its side chain's carboxylic acid group ionizes to an anion. Other listed amino acids like asparagine and histidine are neutral, while lysine is positively charged.
Step-by-step explanation:
The amino acid that has a net negative charge at physiologic pH (~7.4) is Glutamic Acid. This is because the side chains of acidic amino acids such as glutamic acid and aspartic acid contain carboxylic acid groups (-COOH) that ionize to form anions (-COO-) under physiological conditions, leading to a net negative charge. While asparagine and histidine do not carry a net negative charge at this pH, histidine is neutral, and asparagine has a neutral amide group. Lysine, being a basic amino acid with a primary amine group in its side chain, will be positively charged at physiological pH.