Multiple Choice
The following polypeptide N-G-I-F-D-A-Y-G-N-T-W-R-A-P-C-F-V-A is cleaved by chymotrypsin to produce multiple peptide fragments. Based on the specificity of chymotrypsin cleavage, how many peptide fragments are produced?
8. Protein Function
Chymotrypsin
Struggling with Biochemistry?
Join thousands of students who trust us to help them ace their exams!Watch the first videoMultiple Choice
The activity of chymotrypsin drastically changes as the pH fluctuates in the relatively small range of pH 5-9. What amino acid residue in chymotrypsin's active site is most likely to be responsible for this effect of pH?
A
Asp-102.
B
His-157.
C
Ser-195.
D
Tyr-23.
E
Cys-198.
F
Asn-122.
Verified step by step guidance1
Identify the role of pH in enzyme activity: Enzymes have an optimal pH range where they function most effectively. Changes in pH can affect the ionization state of amino acid residues, particularly those involved in the active site, which can alter enzyme activity.
Consider the properties of the amino acids listed: His-157, Asp-102, Ser-195, Tyr-23, Cys-198, and Asn-122. Focus on their side chains and how they might interact with changes in pH.
Recognize that histidine (His) has a side chain with a pKa around 6.0, which is within the pH range of 5-9. This means that histidine can easily gain or lose a proton in this pH range, making it sensitive to pH changes.
Evaluate the role of His-157 in the catalytic triad of chymotrypsin: His-157 is part of the catalytic triad (along with Asp-102 and Ser-195) and plays a crucial role in the enzyme's mechanism by acting as a general base, accepting and donating protons during the reaction.
Conclude that His-157 is most likely responsible for the pH sensitivity of chymotrypsin's activity, as its ability to gain or lose a proton in the pH range of 5-9 can significantly impact the enzyme's catalytic function.
Related Videos
Related Practice
