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Old 04-22-2014
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Default NBME 7 Compounds and Regulatory Enzymes

Hello All,

Does anyone did right question # 26 on section 2 of NBME 7?

The question was about compounds and their regulatory enzymes! and asking specifically compound 5 and its role on regulation of which enzyme ?

Sorry I can not post the entire question, we are not allowed to do that.

Thank you,
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Old 04-24-2014
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Oh! It seems that nobody got the question right!
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Old 04-24-2014
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It inhibited enzyme B...was kind of a tricky question at first, but if you just assume that having too much 5 is going to perform negative feedback and send the pathway the other direction, it's pretty simple.
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Old 04-25-2014
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Quote:
Originally Posted by xorthos View Post
It inhibited enzyme B...was kind of a tricky question at first, but if you just assume that having too much 5 is going to perform negative feedback and send the pathway the other direction, it's pretty simple.
B was the second enzyme after A, B was between (compound 2 and 3). D was the closest to Compound 5 (between 4 and 5). So I chose D and was wrong.
Why did you chose B and not A or E? E is changing the reaction into another direction (compound 2 to 6).

Thanks,
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Old 04-25-2014
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A was a shared enzyme by both pathways. If 5 blocks A then you cut off both enzymatic pathways if you have a high amount of 5, which you wouldn't want to do.

If you have 5 inhibit D, then you're going to have a buildup of intermediate pathway substrates, since the path just stops halfway, and there's nowhere for them to go.

But if 5 inhibits B, then it's inhibiting the entire pathway that leads to 5, but the substrate is still present allowing it to be rerouted down the other path.

(Sorry, it's hard to explain this in text only...if that didn't make sense I'll try to draw a picture and attach it)
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