In feedback inhibition, the substances at the end of a reaction (in this case, CTP, the product) inhibit a previous reaction (in this case, the CTPase reaction). This tells the CTPase that a substantial amount of CTP is present, and to stop engaging in the reaction. The opposite, when a metabolic product facilitates further synthesis of that product, is known as positive feedback. Zymogens are inactive enzyme precursors - examples are pepsinogen and angiotensinogen. Cooperativity refers to the changes in binding affinity of an enzyme with multiple binding sites to its ligands. For example, hemoglobin has four oxygen binding domains; when one oxygen is bound, it facilitates the binding of the second, third, and fourth oxygens. Negative cooperativity is the opposite of this.

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.

Competitive inhibitors bind to the active site of an enzyme via weak, intermolecular bonds (such as hydrogen bonds and hydrophobic interactions) that can be easily broken. This means that increasing substrate concentration will cause the weak bonds between competitive inhibitor and enzyme to break and, subsequently, open up the active site for the substrates. This is why competitive inhibition can be overcome by adding more substrates.

Noncompetitive inhibitors, on the other hand, bind to an allosteric site via strong covalent bonds. Once bound, noncompetitive inhibitors alter the shape of the active site, thereby making it harder for substrates to bind to enzyme. Increasing substrate concentration will not dissociate the strong, irreversible bonds between noncompetitive inhibitor and enzyme allosteric site.

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.

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.

Based on the information, we have seen that  for the enzyme has been unaffected, but the  for the enzyme has been lowered. This type of inhibition is observed with noncompetitive inhibitors.

In this question, we're given a graph of initial reaction velocity as a function of substrate concentration. In addition, we're shown the course of the reaction both in the absence and in the presence of an inhibitor. We're asked to determine the type of inhibition that is occurring.

The most important thing to notice in this graph is that the maximal velocity for both is the same. In other words, adding the inhibitor has no effect on the maximum possible reaction rate. However, the maximal reaction rate will occur only at a higher substrate concentration when in the presence of inhibitor. Thus, we can classify this as competitive inhibition.

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.

A competitive inhibitor acts the increase the  of a reaction, but does not alter the . This does not describe the inhibition on Enzyme A or Enzyme B. A noncompetitive inhibitor decreases the , but does not change the . This is the inhibition that is described on Enzyme A. An uncompetitive inhibitor decreases both the  and the . This is the inhibition that is described on Enzyme B.