There were three catalytic triad residues shown (Ser-His-Asp). Which additional residue was shown? The protein backbone at that location is able to make valuable H-bond contacts with the transition state that forms.

Question

BlackTom AI · Accepted Answer

The question describes a catalytic triad consisting of Ser-His-Asp and asks which additional residue was shown, noting that the protein backbone at that location can form valuable H-bond contacts with the transition state. 
Option 1: Gly. Glycine is the smallest amino acid and often appears in flexible regions or at active-site interfaces where minimal steric hindrance is beneficial; its backbone can participate in stabilizing hydrogen bonds with transition states, which aligns with the description of forming valuable H-bond contacts. This makes Gly a plausible candidate for the additional residue showcased.
Option 2: Thr. Threonine contains a hydroxyl group that can participate in hydrogen bonding, and its side-chain could, in principle, engage in interactions near the active site. However, the prompt emphasizes a residue whose presence and backbone location enable valuable H-bond contacts with the transition state specifically described in this context, and Thr is less commonly highlighted in this precise role alongside a catalytic triad in standard textbook representations.
Option 3: Lys. Lysine has a long, basic side chain capable of electrostatic and hydrogen-bond interactions, but the description emphasizes a residue tied to backbone H-bond contacts with the transition state at that location, which is more characteristic of small residues capable of backbone interactions rather than a bulky, charged side chain like that of Lys. This makes Lys a less likely choice in this context.
Option 4: Pro. Proline is unique in that it imposes conformational rigidity due to its cyclic structure, often affecting backbone phi angles. While Pro can influence local geometry and sometimes participate in hydrogen-bond networks, the description highlighting valuable backbone H-bond contacts with the transition state at the catalytic region is not typically attributed to Pro in classic catalytic triad contexts.
Option 5: Ala. Alanine is another small residue, but unlike Gly, Ala has a methyl side chain that adds steric bulk relative to Gly and can alter backbone conformations. The question’s emphasis on a backbone-mediated hydrogen-bond interaction with the transition state lends more support to a residue that offers maximal backbone accessibility, which Gly more readily provides.
In summary, among the options, Gly best fits the role of an additional residue shown that allows the backbone at that location to form valuable hydrogen-bond contacts with the transition state, consistent with common depictions of catalytic sites and their neighboring residues. The other choices may contribute to active-site chemistry in various contexts, but they do not align as closely with the described backbone-mediated transition-state stabilization.

BIOL3612.MERGED.202610 Activity Questions 3B: Chymotrypsin mechanism

There were three catalytic triad residues shown (Ser-His-Asp). Which additional residue was shown? The protein backbone at that location is able to make valuable H-bond contacts with the transition state that forms.

View Explanation

Log in for full answers

Similar Questions

Which statement is TRUE regarding the active sites of enzymes?

Which one of the follwing statements describes best the common features of enzyme active sites?

The region of an enzyme into which the substrate fits is a:

The HIV drug, Ritonavir, is a competitive inhibitor of HIV protease. One of the challenges of treating HIV is its high mutation rate, which can create resistance to available drugs. Where in the protease enzyme would amino acid changes need to take place in order to make it ineffective?

In a consumer society, many adults channel creativity into buying things

Economic stress and unpredictable times have resulted in a booming industry for self-help products

People born without creativity never can develop it

A product has a selling price of $20, a contribution margin ratio of 40% and fixed cost of $120,000. To make a profit of $30,000. The number of units that must be sold is: Type the number without $ and a comma. Eg: 20000

More Practical Tools for Students Powered by AI Study Helper

Homework AI Solver

Stylized AI Paper Writer

Plagiarism Checker Assistant

Citation AI Academic Writing Tool

In-Class Translation Assistant

AI Note Generator

AI Quiz Answers

Past Exam Questions from University Test Bank

Smart Practice Assistant

Adaptive Practice

Making Your Study Simpler