2019 A Level H2 Chemistry Paper 1 Question 28 - Deduce Products of Hydrolysis by Chymotrypsin
Here's question 28 for 2019 A Level H2 Chemistry Paper 1.
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:
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.
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.
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.
B will give 1 dipeptide and 2 amino acids, hence not the answer.
C will give 2 dipeptides hence this is the answer that we want.
D will give 2 amino acids and 1 dipeptide, hence not the answer.
Topic: Nitrogen Compounds and Proteins, Organic Chemistry, A Level Chemistry, Singapore
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