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
Most impoant 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., MethionineMethionine is activated into S-adenosylmethionine, which then transfers its methyl group to an acceptor. Thus methionine acts as methyl donor in transmethylation reactions.Some of the impoant transmethylation reactions are?Norepinephrine - EpinephrinePhosphatidylethanolamine - PhosphatidylcholineGunaidoacetate 4 CreatineEthanolamine - CholineAcetyl serotonin - SerotoninNucleotides methylated nucleotides