# Biochemistry : Michaelis-Menten Graphs

## Example Questions

### Example Question #1 : Michaelis Menten Graphs

In a Lineweaver-Burk plot, the slope is __________.

Possible Answers:

Correct answer:

Explanation:

A Lineweaver-Burk is a double-reciprocal of the Michaelis-Menten equation. The equation for the graph, in  form is:

From this graph, we can see that the slope is .

### Example Question #1 : Michaelis Menten Graphs

In a Michaelis-Menten plot of enzyme kinetics, the reaction rate is plotted as a function of substrate concentration. Why is it that as substrate concentration increases, the curve of the graph levels off and reaches a plateau?

Possible Answers:

All of the substrate has been converted into product

The enzyme becomes degraded

This only happens when a non-competitive inhibitor is present

This only happens when a competitive inhibitor is present

The enzyme becomes saturated

Correct answer:

The enzyme becomes saturated

Explanation:

In a classic Michaelis-Menten graph, the y-axis represents reaction rate and the x-axis represents substrate concentration. At low substrate concentrations, the reaction rate increases sharply. But as the substrate concentration climbs, the reaction rate begins to increase less and less until it comes to a point where it plateaus into a flat line.

The reason this happens is because the enzyme becomes saturated with substrate. When substrate concentration is low, many of the enzymes in solution aren't doing anything, so they're readily available to convert substrate into product. Thus, adding even just a little bit of substrate will result in a dramatically increased reaction rate. When a high concentration of substrate is present, all of the enzymes in solution are busy. In other words, as soon as an enzyme converts a substrate into product, it immediately becomes occupied with another substrate. Since this process can't occur any faster unless more enzymes are added, all of the other substrate in solution have to wait their turn. Thus, any increase in substrate concentration under these circumstances results in very little, if any, increase in reaction rate.

### Example Question #1 : Michaelis Menten Graphs

Where on a Michaelis-Menten graph is the slope of reaction velocity linear?

Possible Answers:

When enzyme concentration is low

When enzyme concentration is high

It is never linear

When substrate concentration is low

When substrate concentration is high

Correct answer:

When substrate concentration is low

Explanation:

When substrate concentration is high, all of the active sites can be constantly occupied by enzyme.  Further, the active sites can be saturated by enzyme when concentration is very high.  But, when the concentration of substrate is low, the reaction velocity is considered to be linear.

### Example Question #1 : Michaelis Menten Graphs

On a Lineweaver-Burk plot, which of the following is correct?

Possible Answers:

Slope =

Slope =

Y-intercept =

X intercept =

X-axis is

Correct answer:

Slope =

Explanation:

On a Lineweaver-Burk plot, the following are the correct matches regarding points of importance?

X-axis =

Y-axis =

X-intercept =

Y-intercept =

Slope =

### Example Question #5 : Michaelis Menten Graphs

In the presence of a competitive inhibitor, which of the following changes will always be observed on the Lineweaver-Burk plot?

Possible Answers:

The y-intercept for the uninhibited line will be higher than that for the inhibited line

The x-intercept will be closer to the origin for the uninhibited line that for that of the inhibited line

The y-intercept will be the same for the inhibited and uninhibited line

The x-intercept of the inhibited line will be the same for both lines

The lines will always be exactly the same

Correct answer:

The y-intercept will be the same for the inhibited and uninhibited line

Explanation:

will remain the same for an inhibited enzyme when a competitive inhibitor is used. With this information, one can figure out what will happen to the line for an inhibited enzyme on a Lineweaver Burk plot. The y-intercept represents  on these graphs, and so in the presence of a competitive inhibitor, the y-intercept will remain unchanged for an inhibited enzyme. The x-intercept represents . A competitive inhibitor will raise , and so the inhibited enzyme's x-intercept will be closer to the origin.