Which amino acids are negatively charged (acidic) at physiological pH?

The correct response identifies aspartate and glutamate as the amino acids that are negatively charged (acidic) at physiological pH, typically around 7.4. Both aspartate and glutamate contain carboxyl groups in their side chains, which are capable of donating protons (H+) in the physiological pH environment. When these carboxyl groups lose their protons, the amino acids become negatively charged.

At physiological pH, aspartate has a side chain carboxyl group that is ionized and carries a negative charge, while glutamate has an additional carboxyl group, giving it a similar negative charge in this pH range. This characteristic is fundamental to their role in biochemical processes, such as enzyme activities, protein interactions, and neurotransmission.

In contrast, the other groups listed do not possess the same properties that result in a negative charge at physiological pH. Serine and threonine have hydroxyl groups, which do not contribute a negative charge; tyrosine and asparagine have similar properties; lysine and arginine are positively charged due to their amino groups. This context emphasizes the importance of recognizing the acidic nature of aspartate and glutamate in biochemical pathways and interactions.