Question about Central Dogma
MCAT Student
🔬I am referring to a question in the Bio/Biochem 2 Lesson Book on the passage question asking what change occurs in DNA when a point mutation changes a cytosine to a thymine? I selected answer choice D that the phosphate backbone is deformed due to a base pair mismatch, because I reasoned that if a point mutation were to occur on one side of the DNA during replication, then the thymine would be paired with guanine. The correct answer was that one fewer hydrogen bond is formed between base pairs, but wouldn't this necessarily imply that the complementary base pair to that which was mutated would also change? I could see this happening after another replication cycle occurred, but maybe not immediately.
Answers
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An additional question from this same lesson. On the video the last question on the passage about leigh syndrome is different from that which is in the packet. The final question in the packet lists one of the answer choices as an irreversible inhibitor while the video has mixed inhibitor. The correct answer for the question was a noncompetitve inhibitor but while debating the answer based on my prediction I came to the conclusion that it was irreversible. How does one distinguish between noncompetitve and irreversible seeing as they have very similar effects on enzyme inhibition.
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Hi Jacob
For the first question, a base pair mismatch just means that the bases aren't able to hydrogen bond anymore, which means that the lack of an intermolecular interaction is distorting a covalent bond like in the phosphodiester bond. Do you see how the logic doesn't work?
For the second question, you'd need proof to support irreversible modification of the inhibitor to the enzyme. Competitive, noncompetitive, uncompetitive and mixed are all forms of reversible inhibition, and reversible inhibition is assumed unless you're told otherwise.
Hope that helps, and feel free to follow up.
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Thank you for your response. Isn't noncompetitive inhibition rarely observed in nature because observing a reversible inhibitor that decreases the Vmax without impacting the Km would be relatively difficult unless it occurred in a irreversible manner?
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Turns out that most reversible inhibitors are actually mixed in reality (which is just a subtype of noncompetitive), but the MCAT does like to test more simplified situations.
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