This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Amino Acids Basics, Subject name: Biochemistry
The amino acid that lacks chirality 
Select and explain. 
A. Lysine, B. Leucine, C. Histidine, D. Glycine
D: Glycine
Answer: D: Glycine 
Explanation: Ans. is 'd' i.e. Glycine "The Alpha carbon of each amino acid is attached to four different chemical groups and is therefore a chiral or optically active carbon atom. Glycine is the exception because its alpha carbon has two hydrogens substituents (2 H atoms attached to alpha carbon) and is therefore optically inactive (lacks chirality). "All amino acids except glycine exists as two stereoisomers (or optical isomers or enantiomers), designated asD (dextro) &L (levo) forms.All the amino acids found in proteins are of the L-configuration*Also rememberSmallest and simplest amino acid - Glycine*Amino acid responsible for flexibility of proteins is - Glycine*