This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Optically inactive amino acid is/are: 
Select and explain. 
A. Threonine, B. Thyronine, C. Valine, D. Glycine
D: Glycine
Answer: D: Glycine 
Explanation: Ans: d. Glycine Amino acids having an asymmetric carbon atom exhibit optical activity. Asymmetry arises when 4 different groups are attached to the same carbon atomGlycine is the simplest amino acids & has no asymmetric carbon atom & therefore shows no optical activity. All others are optically activeThe mirror image forms produced with reference to the alpha carbon atom, are called D & L isomersIsoleucine er threonine have 2 optically active centres & therefore each has 4 diastereo isomers