This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Structure & Function of Protein, Subject name: Biochemistry
The optically inactive amino acid is: 
Select and explain. 
A. Glycine, B. Serine, C. Threonine, D. Valine
A: Glycine
Answer: A: Glycine 
Explanation: Ans. A. GlycineOptically inactive molecules are those whose mirror images are super imposable and don't have a chiral carbon atom.Out of the 20 standard amino acids glycine is the simplest, optically inactive amino acid.