Indicate which region of the Enzyme Kinetics plot below best c...

Question

Indicate which region of the Enzyme Kinetics plot below best corresponds to each statement.

Enzyme kinetics plot showing initial reaction rate vs substrate concentration with labeled regions A, B, and C.

A) Initial reaction velocity is limited mainly by the [S] present: ______

B) Initial reaction velocity limited mainly by the [E] present: ______

C) The active site of an enzyme is most likely free/unoccupied: ______

D) The active site of an enzyme is most likely occupied by substrate: ______

E) This region includes the points corresponding to Km & ½Vmax: ______

Accepted Answer

Alright. So this practice problem wants us to indicate which region of the enzyme kinetics plot below best corresponds to each of these five statements. And so notice on the right over here what we have is our enzyme kinetics plot, where we have the initial reaction rate or the v naught on the y axis and the substrate concentration and units of molarity on the x axis. And in red here, what we have is our typical enzyme kinetics curve that we see for so many different enzymes, and notice that our curve is labeled with these different regions here, region a, region b is right here, and region c is, of course, up here. So in our problem here, we need to indicate which of these three regions best corresponds with each of the statements. And so starting with statement a here, it says that the initial reaction velocity is limited mainly by the substrate concentration that's present. And so if it's being limited by the substrate concentration, what that's saying is that the substrate concentration must be really, really low, and low substrate concentration corresponds with further to the left on our x axis. And further to the left on the x axis corresponds with region a of our plot. So we can indicate that, statement a best corresponds with region a. So moving on to, statement b, it says that the initial reaction velocity this time is limited mainly by the enzyme concentration that's present. And so, of course, we know that when, an enzyme is approaching its theoretical maximal reaction velocity, or its v max, which is a horizontal asymptote on our enzyme kinetics plot. We know that when the curve here is approaching the Vmax, so essentially in this region here, that the substrate concentration is at saturating levels. So we know that we're at really, really high substrate concentrations here, and really what's limiting the initial reaction rate from increasing further is the amount of enzyme that's present. And so, that would be the enzyme concentration. So what we can say is that it's region C, this region here, that best corresponds with statement B. So moving on to C here, it says that the active site of an enzyme is most likely in the free or the unoccupied state. And so, essentially, we know that the substrate, the substrate is what will bind to the active site of an enzyme. And so if the active site is free or unoccupied by substrate, that that must mean that there is really really low substrate concentration. And so, essentially what we are saying is low substrate concentrations again corresponds with region A here. So we would expect that in region A, that most of our enzymes, active sites would be in the free or unoccupied state. And so moving on to statement d here, it says that the active site of the enzyme is most likely in the occupied, is most likely occupied by substrate. And so, essentially, what that's saying is the complete opposite. So that must be saying that we have a lot of substrate. And so if we have a lot of substrate, we're going to be over here, and that's going to correspond with this region up here. And so we have so much substrate in this region that it's saturating the enzymes. And so, that is going to mean that all of our enzymes would be, have their active sites occupied by substrate. And so that would be region C as well. So now moving on to this last statement here, it says, this region includes the points corresponding to the Kilometers and half of the vmax. So recall from our previous lesson videos that the Kilometers can be defined as the exact concentration that's needed to get the initial reaction velocity equal to half of the v max. And so again, we identified that our v max was this horizontal asymptote where the initial reaction velocity approaches at saturating substrate concentration. And so if we want half of this v max vertically, all we got to do is take half of this horizontal asymptote vertically. So, half of that is going to be somewhere in this region around here, And so this would correspond with about half of the v max. So this is half of v max. And so, now that we have half of the v max here, essentially what we can say, let's move this over a little bit here, so now that we have half of the vmax corresponding at this green line, we know that the exact substrate concentration that corresponds with this half vmax here, so essentially going down from our plot, the Kilometers, would be the exact substrate concentration. So essentially, because this falls, this half v max falls into region b here, we can say that really it's, the Kilometers is associated with region b. So, we can indicate that b here is where we will find the Kilometers. And so that concludes this practice problem, and I'll see you guys in our next video.

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