This is an example of feedback inhibition, as feedback inhibition is a mechanism in which a molecule binds to an enzyme to decrease its activity. The mechanism is now balanced. Blocking an enzyme typically helps correct a metabolic imbalanace or assists in destruction of a pathogen. In this case the ATP binds to a site other than the protein's active site, and since it blocks PFK-1, a feedback inhibition has occurred.

In this question, we're shown a line-weaver burk plot. One of the slopes represents the kinetic profile of an enzyme without inhibitor, while the other slope depicts an enzyme with inhibitor.

When looking at the graph, we notice that the two lines are parallel to one another. What this means is that the y-intercept is changing just as much as the x-intercept. This is a very valuable clue, because this lets us know that the of the reaction is decreasing just as much as that reaction's .

Since we know that both of these values are decreasing, we need to determine which type of inhibition has this characteristic. In competitive inhibition, the increases and the remains unchanged. Thus, this graph cannot be competitive inhibition.

Furthermore, this also cannot be noncompetitive inhibition. And, by extension, this cannot be mixed inhibition, which is just a special case of noncompetitive inhibition. In both of these forms of inhibition, the does indeed decrease. However, the value can either increase, decrease, or stay the same (in mixed inhibition). The value will not change by an amount equal to the change in .

The only other option left is uncompetitive inhibition. Indeed, in this type of inhibition, and are both decreased by the same degree.

In this question, we're presented with a Lineweaver-Burk plot. In the plot, we are shown the parameters of a given enzyme both in the presence and in the absence of an inhibitor. We're asked to identify a true statement.

To begin with, we'll need to understand a few important points about enzyme inhibition. First, it's important to break inhibition up into its different types. Under the category of reversible inhibition, the inhibitor can bind in certain ways to the enzyme, and this will have an effect on the lineweaver-burk plot.

In competitive inhibition, the inhibitor binds only to the enzyme's active site. As a result, the substrate is unable to bind. In this scenario, the for the reaction will not change, but the will increase. In the plot shown in the question stem, this is not the case.

In uncompetitive inhibition, the inhibitor binds to an allosteric site on the enzyme only after substrate has bound. In other words, once the substrate has attached to the enzyme's active site, then the inhibitor will bind. Because the inhibitor can only bind to the enzyme-substrate complex, both the and of the reaction will decrease proportionately. In such a case, the plot will show two lines that are parallel to one another. This is not the case in the plot given to us in the question stem.

In mixed inhibition, the inhibitor is capable of binding to both the enzyme's active site as well as to the enzyme's allosteric site. Because of this, the of the reaction will always decrease, but the of the reaction can either decrease or increase, depending on whether the inhibitor has more affinity for one site over another. Based on the graph, we can see that this is not the case.

Finally, there is a special case of mixed inhibition called noncompetitive inhibition. In this case, the inhibitor binds to both the allosteric site and the active site with equal affinity. Because of this, the of the reaction will decrease, but the of the reaction will remain unchanged. As we can see in the plot shown to us in the question stem, this is the case because both lines intersect on the x-axis, meaning that they have the same value.

Enzymes bind to and stabilize transition states. So a molecule that resembles the transition state of a reaction will be able to bind to the enzyme for that reaction very readily and compete with the binding of the actual transition state. Therefore transition state analogs are competitive inhibitors.

The correct answer is "pure noncompetitive inhibition." Noncompetitive inhibition, or mixed inhibition, is when the inhibitor binds to both the free enzyme and the enzyme-substrate complex, but may not bind equally to both. Competitive inhibitors bind to the free enzyme only at the enzyme’s substrate binding site, thus “competing” with the substrate for the binding site. Uncompetitive inhibitors do not bind the free enzyme but only to the enzyme-substrate complex.

The molecule in the question is classified as an enzyme inhibitor because it inhibits an enzymatic reaction. There are two types of inhibitors; competitive and noncompetitive inhibitors. Competitive inhibitors bind to the active site of the enzyme and prevent substrate from binding. They can be, however, dissociated with the addition of more substrates. This occurs because the substrates can dissociate the reversible bonds between inhibitor and enzyme and bind to active sites. Competitive inhibitors increase (or decrease the affinity of enzyme and substrate) but leave the unaltered. According to the information given in the question, we can conclude that the molecule is a competitive inhibitor.

Noncompetitive inhibitors bind irreversibly to an allosteric site of the enzyme and prevent substrate from binding to the active site. These types of inhibitors decrease the maximum reaction rate but leave the unaltered.

Uncompetitive inhibitors can only bind the ES complex, whereas competitive and non-competitive inhibitors do not require the enzyme to be complexed with the substrate. , which describes the maximum reaction velocity of the enzyme, is decreased because the inhibitor slows the dissociation of the substrate from the enzyme, thereby slowing the rate at which the enzyme can interact with other substrate molecules.

This question is presenting us with a situation in which a chemical is being added to a mixture of enzyme and substrate, and its effects on the kinetic parameters of the reaction are observed. We're told that the and for this reaction both become reduced. We then are asked to identify which term best describes the added chemical.

To begin with, let's take note that all of the answer choices are some kind of inhibitor. Thus, we know that the chemical we're adding to the mixture is an inhibitor of some type. The challenge is in identifying which type of inhibition is happening. For this question, we'll need to have familiarity with each type of inhibition in order to identify the correct answer.

Let's start with what we know. Both the and the are being decreased. Right away, we can rule out competitive inhibition because the should remain the same.

We should also be able to rule out feedback inhibition right off the bat, as this kind of inhibition involves the products of a reaction putting a halt on the reaction that led to its production.

Next, we can also realize that two of the answer choices are so similar that they are actually saying nearly the same thing. Mixed inhibition is a case in which the inhibitor binds to the enzyme regardless of whether substrate is also bound to the enzyme. However, with mixed inhibition, the inhibitor shows greater affinity for either the free enzyme or the enzyme-substrate complex. In such a case, the for the reaction is expected to fall, but the can either increase or decrease.

Noncompetitive inhibition is a special type of mixed inhibition, in which the inhibitor binds both the free enzyme and the enzyme-substrate complex with equal affinity. In such a situation, the of the reaction will fall, but the will remain unchanged.

And finally, we look at uncompetitive inhibition, which is the correct answer. In this type of inhibition, the inhibitor binds only to the enzyme-substrate complex rather than the free enzyme. It does so by binding to an allosteric site, which is distinct from the active site to which substrate binds. Thus, there is no way to out-compete the inhibitor by adding more and more substrate, as can be done in competitive inhibition. The end result of this is that the becomes irrecoverably lowered. And since this value becomes less, the substrate concentration needed to obtain half of that reduced value (the ) also becomes decreased.

Competitive inhibition involves the substrate's access to the active site. In the case of competitive inhibition, the inhibitor blocks the substrate from the active site. As a result, the is unchanged, but the is increased. Recall that is the substrate concentration at which the reaction rate is . Additionally, the reaction rate will increase with increased concentration of competitive inhibitor and substrate, because they are competing for the active site, causing an increase in reaction rate.

Uncompetitive inhibition refers to an inhibitor that binds to the enzyme-substrate complex. This limits the amount of enzyme-substrate complexes that can be made into products, and so is decreased. It also decreases Km because the apparent affinity is increased due to the inability of the enzyme-substrate complexes to become unbound.