2019 A Level H2 Chemistry Paper 1 Question 28 - Deduce Products of Hydrolysis by Chymotrypsin

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Here's question 28 for 2019 A Level H2 Chemistry Paper 1.

2019 p1 q28 qn

Given the activity of chymotrypsin, we need to deduce which option will form 2 dipeptides when hydrolysed by the enzyme.

First let's interprete the struture of pentapeptide W.

Recall the primary structure of proteins has a very predictable repeat unit:

2019 p1 q28 protein primary structure repeat unit

Position 1 - amine group
Position 2 - carbon with R group
Position 3 - acid group

Therefore we can find out the positions 1, 2 and 3 for W.

2019 p1 q28 repeat unit in W

Next, we know that chymotrypsin will hydrolyse the peptide bond on the acid or carboxyl side of a residue with an aromatic ring.

So we can look at W, find the R groups with aromatic ring, break the peptide bond on the acid side, and figure out the products X (dipeptide), Y (dipeptide) and Z (amino acid) formed.

2019 p1 q28 deduce products when W hydrolysed by chymotrypsin

Once we understand how chymotrypsin functions, we can now apply this to the options and see which one gives us 2 dipeptides when hydrolysed with chymotrypsin.

A will give 1 tripeptide and 1 amino acid, hence not the answer.

2019 p1 q28 A hydrolysed by chymotrypsin

B will give 1 dipeptide and 2 amino acids, hence not the answer.

2019 p1 q28 B hydrolysed by chymotrypsin

C will give 2 dipeptides hence this is the answer that we want.

2019 p1 q28 C hydrolysed by chymotrypsin

D will give 2 amino acids and 1 dipeptide, hence not the answer.

2019 p1 q28 D hydrolysed by chymotrypsin

Topic: Nitrogen Compounds and Proteins, Organic Chemistry, A Level Chemistry, Singapore

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