On complete hydrolysis,a polypeptide gives two glycine,one alanine,one valine,and one serine residue.Partial hydrolysis gives the following fragments: Gly-Ser,Val-Gly,Ser-Val,and Ala-Gly.What is the primary structure of the polypeptide?

Question

Quizplus · Accepted Answer

From the complete hydrolysis, we know that there are two glycine, one alanine, one valine, and one serine residue. Thus, the possible sequences are:

1) Gly-Gly-Ala-Val-Ser
2) Gly-Ala-Gly-Val-Ser
3) Gly-Ser-Val-Gly-Ala
4) Ala-Val-Ser-Gly-Gly
5) Ala-Gly-Ser-Val-Gly

From the partial hydrolysis, we have the following fragments: Gly-Ser, Val-Gly, Ser-Val, and Ala-Gly. Looking at each possible sequence, we can determine which sequence fits best:

1) Gly-Gly-Ala-Val-Ser :
- No glycine-serine or serine-valine fragment can be obtained
- Therefore, this sequence cannot be our answer
 
2) Gly-Ala-Gly-Val-Ser : 
- No glycine-serine or serine-valine fragment can be obtained
- Therefore, this sequence cannot be our answer

3) Gly-Ser-Val-Gly-Ala :
- Gly-Ser fragment matches with this sequence
- Val-Gly fragment matches with this sequence
- Ser-Val fragment matches with this sequence
- Ala-Gly fragment matches with this sequence
- This sequence fits all the fragments from partial hydrolysis
- Therefore, this sequence is our answer
 
4) Ala-Val-Ser-Gly-Gly :
- No glycine-serine or serine-valine fragment can be obtained
- Therefore, this sequence cannot be our answer
 
5) Ala-Gly-Ser-Val-Gly :
- Gly-Ser fragment matches with this sequence
- Val-Gly fragment matches with this sequence
- Ser-Val fragment matches with this sequence
- Ala-Gly fragment matches with this sequence
- This sequence fits all the fragments from partial hydrolysis
- Therefore, this sequence is also a possible answer

However, the sequence from choice (D) Ala-Gly-Ser-Val-Gly matches all the fragments from partial hydrolysis and is the most likely primary structure of the polypeptide.

On Complete Hydrolysis,a Polypeptide Gives Two Glycine,one Alanine,one Valine,and One