Multiple Choice
Which of the following would not be a reversible post-translational modification?
7. Enzyme Inhibition and Regulation
Post Translational Modification
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An enzyme's active site has high affinity for a polar charged substrate. How will methylation of the active site affect the reaction rate of the enzyme?
A
Affinity for the charged substrate will increase thereby increasing reaction rate.
B
Affinity will remain unchanged, and therefore will be independent of the modification.
C
Affinity for the substrate will decrease, lowing the reaction rate.
Verified step by step guidance1
Understand that the enzyme's active site is initially designed to have a high affinity for a polar charged substrate, which means it likely contains complementary charged or polar groups that facilitate substrate binding.
Consider the effect of methylation: Methylation involves the addition of a methyl group (CH₃) to a molecule. This group is non-polar and hydrophobic, which can alter the chemical environment of the active site.
Analyze how the addition of a non-polar methyl group to the active site could affect its interaction with the polar charged substrate. The introduction of non-polar characteristics can disrupt the electrostatic interactions or hydrogen bonds that are crucial for binding the polar charged substrate.
Predict the outcome of this modification: The decrease in polar or charged interactions due to methylation will likely reduce the affinity of the active site for the polar charged substrate.
Conclude that with reduced affinity, the enzyme's ability to bind the substrate effectively is compromised, leading to a decrease in the reaction rate, as the enzyme-substrate complex formation is a key step in catalysis.
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