Allosteric Kinetics - Video Tutorials & Practice Problems
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Allosteric Kinetics
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Video transcript
So now that we've introduced allosteric enzymes, in this video, we're going to talk about how allosteric enzymes display allosteric kinetics. And so these allosteric enzymes are actually pretty easy for biochemists to identify and that's because allosteric enzymes behave very very differently than the Michaelis Menten enzymes that we covered in our previous lesson videos. And so this includes responding differently to changes in substrate concentration as well as to the presence of inhibitors. And so it turns out that allosteric enzymes, most allosteric enzymes display a sigmoidal curve or an s shaped curve on a kinetics plot instead of a rectangular hyperbola like Michaelis Menten enzymes do. And so if we take a look at our image down below, notice on the left, enzyme kinetics plot, we're showing you a Michaelis Menten enzyme, and it's forming the same shape that we've seen so many times before in our previous lesson videos referred to as a rectangular hyperbola. Whereas, if we take a look at the enzyme kinetics plot over here on the right, notice that we're showing an allosteric enzyme instead of a Michaelis Menten enzyme. And instead of showing a rectangular hyperbola, it's showing this s shaped curve here which is referred to as a sigmoidal curve. Now, recall that the Michaelis constant kilometers is the exact substrate concentration that allows for half of the v max. And so it turns out that the Michaelis constant variable, k m, only applies to Michaelis Menten enzymes. And so the substrate concentration that allows for half of the v max for allosteric enzymes is represented by the variable k 0.5. And so k 0.5 is pretty much the allosteric enzyme equivalent to the Michaelis constant kilometers for the Michaelis Menten enzymes. And so also on that note, the Michaelis Menten equation only applies for Michaelis Menten enzymes and the Michaelis Menten equation does not apply for allosteric enzymes. So these are definitely some differences to take note about allosteric kinetics. And so, this here concludes our introduction to allosteric kinetics and we'll continue to learn more about allosteric kinetics as we move forward in our course. So I'll see you guys in our next video.
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Problem
Problem
Which of the following statements regarding allosteric kinetics is false?
A
The rate of an allosteric enzyme reaction is dependent on substrate concentration [S].
B
The reaction velocity and substrate concentration always proportionally change in a Lineweaver-Burk plot.
C
At saturating [S], the kinetics of an allosteric enzyme will follow the Michaelis-Menten model.
D
Allosteric enzymes display second order kinetics leading to sigmoidal curvature on a kinetics plot.
E
None are false because all of the above are true.
3
concept
Allosteric Kinetics
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1m
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Video transcript
So another way for biochemists to pretty easily identify allosteric enzymes is by plotting the enzyme enzyme kinetic data onto a line weaver Burk plot. And that's because allosteric enzyme kinetic data does not actually form a straight line on a Lineweaver Burk plot like the enzyme kinetic data of Michaelis Menten enzymes do. And so notice down below over here on the left hand side, we have a Lineweaver Burk plot showing the enzyme kinetic data of a Michaelis Menten Enzyme. And notice that the enzyme kinetic data of the Michaelis Menten Enzyme forms a straight line on the Lineweaver Burk plot. And so here we can write in straight line. And so of course what this means is that the Line Weaver Birke equation is going to apply for Michaelis Menten enzymes. However, if we take a look at the line weaver Burk plot over here on the right hand side, notice it's showing the enzyme kinetic data of the allosteric enzyme. And notice that the enzyme kinetic data of an allosteric enzyme plotted onto a line with Burke plot does not form a straight line. And so this, of course, means that the Lineweaver Burke equation does not apply to allosteric enzymes. And again, it's pretty easy for biochemists to identify these allosteric enzymes when they plot the enzyme kinetic data onto the Lineweaver Burk plot. And so this here concludes our introduction to allosteric enzyme kinetics and we'll be able to get a little bit of practice in our next, video. So I'll see you guys there.
4
concept
Allosteric Kinetics
Video duration:
5m
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Video transcript
So another feature that allosteric enzymes display that Michaelis Menten enzymes don't is this threshold effect. So let's explain this a bit further. So at very, very low substrate concentrations, it turns out that Michaelis Menten enzymes are actually more sensitive to changes in substrate concentration than allosteric enzymes. And we can actually see that down below in our enzyme kinetics plot where this black curve here represents the Michaelis Menten enzymes and the blue curve here represents allosteric enzymes. And so, notice here we're specifically focusing on low substrate concentration. So somewhere around this range right here on the x axis. And so at these low substrate concentrations, notice that the allosteric enzyme pretty much doesn't even respond to changes in substrate concentration. Whereas the Michaelis Menten enzyme definitely does respond to, changes in concentration, when it is low like this. And so that's exactly what we're mentioning up above in this line right here. Now it turns out that however, eventually a threshold substrate concentration is going to be reached. And once this threshold substrate concentration is reached, this is where allosteric enzymes actually become more sensitive, much more sensitive to the changes in substrate concentration. And so notice down below in our, plot here that the threshold substrate concentration And so notice that once this threshold substrate concentration is reached, the allosteric enzyme is much much more sensitive to changes in substrate concentration. Now ultimately, it, this leads to the initial reaction velocity or the v naught of the allosteric enzymes, to approach the v max within a smaller and a more narrow range of substrate concentration. And so we can also see that down below and the ranges are represented by these bars that we have below the x axis here, the blue bar and the gray bar. The blue bar corresponds with the allosteric enzyme and the gray bar here corresponds with the Michaelis Menten enzyme. And so you can see that, once we have, the threshold substrate concentration reached, the allosteric enzyme approaches v max in a very, very narrow substrate concentration. However, for the Michaelis Menten enzyme, it pretty much goes from 0 all the way up to v max within a much, much wider range. And again, that's pretty much what we were saying up above in this line right here. And so all of this here actually creates what's known as the threshold effect. And so, again, the threshold effect is something that allosteric enzymes display that Michaelis Menten enzymes don't. And so, really when it comes down to it, the threshold effect just says that below a certain substrate concentration, there's pretty much very little to no allosteric enzyme activity. And so again, here's the threshold substrate concentration and below the sub threshold substrate concentration, the allosteric enzyme has pretty much 0 to no activity. But once the threshold substrate concentration is reached, the allosteric enzymes activity gets turned on and it can get up to v max pretty pretty quickly. And so really this threshold substrate concentration acts like an on and off switch for the allosteric enzyme. Whereas for the Michaelis Menten enzyme, it's pretty much always on as long as there's some substrate concentration, the Michaelis Menten enzyme is always going to be on. And so you can see how, this threshold effect feature of allosteric enzymes really gives allosteric enzymes another form of regulation that, cells can use to regulate their metabolic pathways. And so, this here concludes our introduction here to the threshold effect of allosteric enzymes and we'll be able to get a little bit of practice as we move forward in our course. So I'll see you guys in our next video.
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Problem
Problem
Because of the _____________ substrate-binding-site(s) & conformation(s) on an allosteric enzyme, the range of [S] to reach the Vmax is _______________ for allosteric enzymes than it is for Michaelis-Menten enzymes.