Question

A tetrapeptide has - COOH group on alanine. This produces glycine (Gly), valine (Val), phenyl alanine (Phe) and alanine (Ala), on complete hydrolysis. For this tetrapeptide, the number of possible sequences (primary structures) with – NH₂ group attached to a chiral center is__

Answer 1

Because –COOH group of tetrapeptide is intact on alanine, its NH₂ must be participating in condensation. 

∴ Alanine is at one terminus, – – – A. 

To fill the 3 blanks, possible options are:

(i) When NH₂ group attached to non chiral carbon

(ii) When NH₂ group attached to chiral carbon

where, 

Glycine (G) 

Valine (V) 

Phenyl alanine (P) 

Alanine (A) 

So the number of possible sequence are 4.