In terms of the new MCAT, is the noncompetitve inhibitor the same thing as mixed inhibitor?
Inhibitor
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Tough to say if the AAMC will ask examinees to make the distinction between the 2, but one does exist.
While a classical noncompetitive inhibitor and a mixed inhibitor (which can be thought of as a type of general noncompetitive inhibitor) are both going to reduce the Vmax of the reaction, the difference is seen in the Km value.
A classical noncompetitive inhibitor (one that has no effect on substrate to enzyme binding) does not alter the Km value, while the mixed inhibitor, which reduces substrate affinity, increases the Km value.
While a classical noncompetitive inhibitor and a mixed inhibitor (which can be thought of as a type of general noncompetitive inhibitor) are both going to reduce the Vmax of the reaction, the difference is seen in the Km value.
A classical noncompetitive inhibitor (one that has no effect on substrate to enzyme binding) does not alter the Km value, while the mixed inhibitor, which reduces substrate affinity, increases the Km value.
But the AAMC MCAT content description lists it as:
Inhibition
-Competitive
-Non-competitive
-Mixed (BC)
-Uncompetitive (BC)
According to the Khan's video, "uncompetitive" inhibitor matches the description of your classic non-competitive inhibitor. And according to Khan's video, noncompetitve inhibitor is the same thing as mixed inhibitor? But I'm not sure if these are right, looking up on google confuses me even more as people use "uncompetitive" and "non-competitive" interchangeably, while the new MCAT seems to want us to differentiate these two.
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Non competitive: decrease Vmax but does not change Km because the affinity isn't changed. LB plot: bigger slope with inhibitor, but same x-intercept.
Uncompetitive: also allosteric binding but it binds the enzyme that already has a substrate. Lowers both Km and Vmax. The LB plot has two parallel lines.
Uncompetitive: also allosteric binding but it binds the enzyme that already has a substrate. Lowers both Km and Vmax. The LB plot has two parallel lines.
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This definitely can be confusing, and so my bet would be that the MCAT does not test you on a strict, minuscule distinction because that'd be unlike them.
Uncompetitive and non-competitive inhibition are not the same thing.
Let me take a look at the Khan videos to see if I help with the confusion and I'll edit this in a few hours.
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Ok so I see what you're talking about in the video
Mixed inhibition is a type of overall "non-competitive inhibition." Sort of like stereoisomers is a type of isomers. There exists a pure non-competitive inhibitor that does not change the Km value (i.e. the inhibitor in binding to the enzyme does not change it's affinity for the substrate), while there also exists the mixed inhibitor that does affect Km (decreases it) by the way it binds. Both decrease Vmax.
A site that might clarify it further for you is:
http://www.uvm.edu/~mcase/courses/chem205/lecture13.pdf
Look about half way down. Admittedly it can be confusing, but remember the distinction between the 2.
Cheers!
Mixed inhibition is a type of overall "non-competitive inhibition." Sort of like stereoisomers is a type of isomers. There exists a pure non-competitive inhibitor that does not change the Km value (i.e. the inhibitor in binding to the enzyme does not change it's affinity for the substrate), while there also exists the mixed inhibitor that does affect Km (decreases it) by the way it binds. Both decrease Vmax.
A site that might clarify it further for you is:
http://www.uvm.edu/~mcase/courses/chem205/lecture13.pdf
Look about half way down. Admittedly it can be confusing, but remember the distinction between the 2.
Cheers!
