This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of protein and amino acid, Subject name: Biochemistry
Cysteine is formed from 
Select and explain. 
A. Methionine and serine, B. Methionine and glycine, C. Alanine and glycine, D. Serine and glycine
A: Methionine and serine
Answer: A: Methionine and serine 
Explanation: Serin+Homocystein ------->Cysteine+Homoserin.Homocystein is synthesized from Methionine.Ref: DM Vasudevan - Textbook of Biochemistry, 7th edition, page no: 217, Fig no 16.15