Cysteine is formed from -

Ans. is 'a' i.e., Methionine and Serine o Cysteine, while not nutritionally essential, is formed from methionine, which is nutritionally essential. Following conversion of methionine to homocysteine , homocysteine and serine form cystathionine, whose hydrolysis forms cysteine and homoserine .o The sulfur of cysteine derives from methionine and the carbon skeleton from serine.