Q7 Evolutionary Changes Promoting More Enzyme-Substrate Binding
10 Points
Grading comment:
Consider the evolution of an enzyme. Which of the following evolutionary changes would cause the individual enzyme to be bound to substrate a greater percentage of the time? (Equivalently, which of the following changes would cause a greater fraction of enzyme molecules to be bound to substrate, on average, at any given time and for any given [S]?) Mark all that apply.
Choice 1 of 4: An existing amino acid that is unable to interact with the transition state is replaced with an amino acid that can form a stabilizing hydrogen bond with that transition state.
Choice 2 of 4: An amino acid is added to the active site that can form an extra hydrogen bond with a part of the substrate far from where the catalytic chemistry occurs. This extra hydrogen bond causes the substrate to be more tightly attached to the enzyme's binding site, but does not affect the transition state energy.
Choice 3 of 4: An amino acid that carries a negative charge and interacts with a positively charged transition state is replaced with an amino acid that is hydrophobic.
Choice 4 of 4: A change in the active site structure alters the pKa of an active site amino acid so that the amino acid has a pKa closer to 7. This amino acid is involved in a proton transfer that is part of the reaction's rate-limiting step.