can someone explain the difference between competitive, non-competitive, and uncompetitive inhibs?

mrh125

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and how they relate to the michaelis-menten equation/what we should know about them for the mcat?

Aside from the oxygen-hemoglobin dissociation curve (i understand that super well now. thanks guys) this is the one bio concept that is really tripping me up. I think I understand competitive ones the best because they just directly compete for access to the active site (like CN- vs o2) and they have an increased (or decreased?) Kmax. Uncompetitive and non-competitive ones just confuse me though. I think uncompetitive ones bind to the substrate complex and deactivate it so the other molecule can't bind to it and non-competitive inhibitors can bind to the substrate or enzyme(?). I think non-competitive has an increased or decreased vmax value too, while un-competitive has decreased vmaxes and kmaxes.

is that right and what does this mean/how is this expressed graphically? I think a bit of my misunderstanding comes from not understanding the michaelis-menten equation well.
 

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Straight from the AAMC outline:

MOLECULAR BIOLOGY: ENZYMES AND METABOLISM

A. Enzyme Structure and Function
1. Function of enzymes in catalyzing biological reactions
2. Reduction of activation energy
3. Substrates and enzyme specificity

B. Control of Enzyme Activity
1. Feedback inhibition
2. Competitive inhibition
3. Noncompetitive inhibition


Notice that "uncompetitive inhibition" isn't on there. So don't worry about it!

As for the other two:

Competitive: just what the name says. The inhibitor competes for the active site. Vmax remains unchanged, though.

Since Vmax can be thought of as "how fast could the reaction go if I had infinite substrate?" then a bit of competitive inhibitor isn't going to change that. If you had infinite substrate, the substrate would so vastly out-compete the inhibitor that you'd still reach Vmax.

Noncompetitive: the inhibitor binds to some other part of the enzyme and shuts it down. This functionally removes the enzyme from the system. With less enzymes available, Vmax goes down.

This is one of those topics that your MCAT books should probably do a pretty good job with. If you've read them over two or three times and are still having trouble, check out mcat-review.org, wikipedia, wikipremed, or Khan academy videos.

Good luck! :)