This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Structure and function of protein, Subject name: Biochemistry
Which of the following amino acids have side chains that are negatively charged under physiological conditions? 
Select and explain. 
A. Aspaic acid, B. Histidine, C. Tyrosine, D. Serine
A: Aspaic acid
Answer: A: Aspaic acid 
Explanation: The side chains of the acidic amino acids, aspaic acid and glutamic acid, are negatively charged above pH 3; in their ionized state, they are often referred to as aspaate and glutamate. Asparagine and glutamine are, respectively, the amides of aspaic acid and glutamic acid. Ref: Voet Fundamentals of Biochemistry 4th Edition Pg no 82.