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
Most important amino acid which acts as methyl group donor- 
Select and explain. 
A. Cysteine, B. Methionine, C. Tyrosine, D. Tryptophan
B: Methionine
Answer: B: Methionine 
Explanation: Ans. is 'b' i.e., Methionineo Methionine is activated into S-adenosylmethionine, which then transfers its methyl group to an acceptor. Thus methionine acts as methyl donor in transmethylation reactions.o Some of the important transmethylation reactions are-i) Norepinephrine - Epinephrineii) Phosphatidylethanolamine - Phosphatidylcholineiii) Gunaidoacetate - Creatineiv) Ethanolamine - Cholinev) Acetyl serotonin - Serotoninvi) Nucleotides - methylated nucleotides