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Direction (21 - 25): All proteins are made up of \[\alpha \]-amino acids which act as the building blocks, \[\alpha \]-amino acids that are synthesized in the body, are known as non-essential \[\alpha \]-amino acids while the one which the body fails to synthesise, are called essential \[\alpha \]-amino acids. All of them exist as dipolar ions also known as Zwitter ions. For all the \[\alpha \]- amino acids, there is a certain pH of the medium known as isoelectric point at which the dipolar ions behave as electrically neutral species. In acidic medium, the ion migrates towards cathode while in basic medium, it migrates towards anode on passing electric current.

(Source : Internet)

Which of the following is not an essential \[\alpha \]-amino acid?

A) Lysine                          

B) Phenylalanine

C) Valine                          

D) Alanine.