Suppose the data on the right is plotted onto a Lineweaver-Bur...

Question

Suppose the data on the right is plotted onto a Lineweaver-Burk plot to obtain a straight line.

A) What is the value of the y-intercept of the line? ____________

B) What is the value of the x-intercept of the line? ____________

Accepted Answer

Alright. So this practice problem wants us to consider the following enzyme catalyzed reaction shown right here, where we have substrate A being converted into product B, and it says, suppose that the enzyme kinetic data for this reaction, which is shown in this chart right here down below, is actually inverted and plotted onto a Lineweaver Burk plot to obtain a straight line. And so notice if we take a look at this chart down below in the first column, what we have is the concentration of our substrate a in units of micromolar, and in the second column what we have is the initial reaction velocity for the enzyme catalyzed reaction in units of micromoles per minute. And so notice that part a is here is asking us, what is the value of the y intercept of the line that we get from plotting the data onto a Line Weaver Burk plot? And so what we need to recall from our previous videos is that a Lineweaver Burk plot is also known as a double reciprocal plot. And so in order to plot this data onto a Lineweaver Burk plot, we're going to need to take the reciprocals of both columns, the substrate concentration, as well as the initial reaction velocity. And so we can go ahead and draw a sketch of our Lineweaver Burk plot, and so notice here that we have the initial reaction velocity reciprocal on the y axis and the reciprocal of the substrate concentration on the x axis. And so once we take the reciprocals of all of these numbers, we can plot them onto our Lineweaver Burk plot, as we see here. So each of these points represents the 11 rows of, data points that we have in our chart over here. And so once we plot all of our data, we're going to need to determine the line of best fit for this data, which would look something like this. And then we can determine the equation of our line of best fit, and recall that the equation of a line is just y equals m x plus b. And the most important information on a Lineweaver Burk plot is actually revealed through the y and the x intercepts. And since part a here is asking us about the y intercept, we're going to focus on that first. So the y intercept is going to be where our line crosses the y axis, and so that's going to be right at this specific point right here. And so, recall from our previous lesson videos that the y intercept, just like pretty much everything else on a line weaver Burk plot, is going to be a reciprocal. So it's going to be one over something and that something, for the y intercept, it's going to be associated with the y axis and reaction velocities are associated with the y axis. So we know that's going to be the reciprocal of the maximum reaction velocity max. And so, in order to determine the y intercept, like part a is asking us, we're going to need to determine what the v max is. And so when we take a closer look at this data over here on our chart, notice that the substrate concentration is steadily increasing up to a point where the, increases in concentration get so, so large that the initial reaction velocity is not changing at all. And so that suggests that the substrate concentrations are saturating our enzymes, and remember, when an enzyme is saturated with substrate, the initial reaction velocity will approach the v max. And so this, indicates saturating substrate concentrations, and these are the initial reaction velocities that are approaching the vmax. So we can say that our vmax is indicated by this value here, which which is a 180 micromoles per minute. And so what we can do is say that our vmax is equal to this 180. So we can say that it's gonna be 1 over 180 micromoles per minute. And really this is the y intercept value that we are looking for, that the problem is asking us about. Notice that the problem is not asking us about the vmax, it is asking us about the y intercept. And so for our answer, we can say that it is 1 over 180 micromoles per minute, and that is our answer. So moving on to part b, it's asking us what is the value of the x intercept of the line? And, of course, we know that the x intercept is going to be where our line here crosses the x axis, which is going to be right at this point right here. And so recall from our previous lesson videos that the x intercept, just like pretty much everything else, is going to be a reciprocal. So it's going to be 1 over something, and that something is going to be associated with the x axis, and we know that substrate concentrations are associated with the x axis. And so, we know that the kilometers is an exact substrate concentration. And so also recall that because on a Lineweaver Burk plot, the x intercept always falls into this negative region of the x axis that the x intercept is always going to have a negative value, which means that we need to remember to include the negative on this one up here. And so we need to determine the kilometers in order to determine the value of the x intercept. And so we know that the kilometers is the exact substrate concentration that allows the initial reaction velocity to be half of the v max. And so if we take half of our v max, half of 180 is 90, and notice that 90 is showing up right here on our, plot. And is showing up right here on our, plot. And so this represents half of the v max, and the substrate concentration that's associated with half of the v max is 87.5 micromolar. And so it's this substrate concentration right here that represents our kilometers value. And so now that we know that we can plug it into our expression here, so we're going to have negative one over 87 point 5, and the units are micromolar. And so really, this is the value for our x intercept that we are looking for. And so we can go ahead and plug that in up above negative one over 87.5 micromolar. And so this here concludes our 2 part practice problem and I'll see you guys in our next video.

Struggling with Biochemistry?

Suppose the data on the right is plotted onto a Lineweaver-Burk plot to obtain a straight line.

A) What is the value of the y-intercept of the line?
B) What is the value of the x-intercept of the line?

Watch next

Lineweaver-Burk Plot practice set

Struggling with Biochemistry?

Suppose the data on the right is plotted onto a Lineweaver-Burk plot to obtain a straight line.A) What is the value of the y-intercept of the line? ____________B) What is the value of the x-intercept of the line? ____________

Watch next

Lineweaver-Burk Plot practice set

Suppose the data on the right is plotted onto a Lineweaver-Burk plot to obtain a straight line.

A) What is the value of the y-intercept of the line?
B) What is the value of the x-intercept of the line?