Enzyme Regulation
Help Questions
GRE Subject Test: Biochemistry, Cell, and Molecular Biology › Enzyme Regulation
On a Lineweaver-Burk plot, an inhibited enzyme is shown to have a less negative x-intercept than the uninhibited enzyme, but the y-intercept remains the same. The type of inhibition displayed is __________ and the inhibited reaction has a __________ 
competitive . . . larger
competitive . . . smaller
non-competitive . . . larger
non-competitive . . . smaller
Explanation
The x-intercept on a Lineweaver-Burk plot tells us the negative reciprocal of 
Because the x-intercept is less negative, this tells us that the inhibited reaction has a larger 
On a Lineweaver-Burk plot, an inhibited enzyme is shown to have a less negative x-intercept than the uninhibited enzyme, but the y-intercept remains the same. The type of inhibition displayed is __________ and the inhibited reaction has a __________
competitive . . . larger
competitive . . . smaller
non-competitive . . . larger
non-competitive . . . smaller
Explanation
The x-intercept on a Lineweaver-Burk plot tells us the negative reciprocal of
Because the x-intercept is less negative, this tells us that the inhibited reaction has a larger
How is pepsinogen activated in the stomach?
A portion is cleaved, activating the enzyme
It is phosphorylated by another enzyme
It is activated by the temperature change in the stomach lumen
Cofactors bind to the enzyme, increasing its efficiency
Explanation
Once in the stomach lumen, pepsinogen finds itself in a very acidic environment. The acidic environment cleaves an amino acid sequence from pepsinogen, turning it into the active enzyme pepsin. This type of activation causes pepsin to only activate in the stomach lumen where it is needed.
How is pepsinogen activated in the stomach?
A portion is cleaved, activating the enzyme
It is phosphorylated by another enzyme
It is activated by the temperature change in the stomach lumen
Cofactors bind to the enzyme, increasing its efficiency
Explanation
Once in the stomach lumen, pepsinogen finds itself in a very acidic environment. The acidic environment cleaves an amino acid sequence from pepsinogen, turning it into the active enzyme pepsin. This type of activation causes pepsin to only activate in the stomach lumen where it is needed.
You have an enzyme solution and you add an inhibitor molecule and observe a marked decrease in enzyme activity. You increase the substrate concentration but this does not lead to any observable increase in enzyme activity. What can you conclude about your inhibitor?
That it is a noncompetitive inhibitor
That it is a competitive inhibitor
That is it an inorganic inhibitor
That it binds the enzyme's active site
That it is a kinase
Explanation
Noncompetitive inhibitors bind to enzymes away from the active site (allosteric) and distort it, reducing its affinity for substrate. Since they do not directly compete with substrate for enzyme binding, increasing the substrate concentration in the presence of a noncompetitive inhibitor will have no affect. While enzyme inhibitors include both organic and inorganic molecules, there is not enough information in the question stem to conclude the chemical classification of the inhibitor.
You have an enzyme solution and you add an inhibitor molecule and observe a marked decrease in enzyme activity. You increase the substrate concentration but this does not lead to any observable increase in enzyme activity. What can you conclude about your inhibitor?
That it is a noncompetitive inhibitor
That it is a competitive inhibitor
That is it an inorganic inhibitor
That it binds the enzyme's active site
That it is a kinase
Explanation
Noncompetitive inhibitors bind to enzymes away from the active site (allosteric) and distort it, reducing its affinity for substrate. Since they do not directly compete with substrate for enzyme binding, increasing the substrate concentration in the presence of a noncompetitive inhibitor will have no affect. While enzyme inhibitors include both organic and inorganic molecules, there is not enough information in the question stem to conclude the chemical classification of the inhibitor.
How does a noncomeptitive inhibitor affect an enzyme?
Lowers the maximum rate of the enzymatic reaction
Raises the maximum rate of the enzymatic reaction
Raises the Michaelis constant of the enzyme
Lowers the Michaelis constant of the enzyme
Explanation
A noncompetitive inhibitor acts to decrease how fast the enzyme can act on substrates. It accomplishes this by lowering the maximum rate at which it can create products. Noncompetitive inhibitors do not alter the enzyme's Michaelis constant.
How does a noncomeptitive inhibitor affect an enzyme?
Lowers the maximum rate of the enzymatic reaction
Raises the maximum rate of the enzymatic reaction
Raises the Michaelis constant of the enzyme
Lowers the Michaelis constant of the enzyme
Explanation
A noncompetitive inhibitor acts to decrease how fast the enzyme can act on substrates. It accomplishes this by lowering the maximum rate at which it can create products. Noncompetitive inhibitors do not alter the enzyme's Michaelis constant.
A researcher has designed a new type of inhibitor that binds at the active site of an enzyme. What type of inhibition does this molecule display?
Competitive inhibition
Noncompetitive inhibition
Uncompetitive inhibition
Suicide inhibition
Explanation
Because the inhibitor binds at the active site, it is actively competing with the ligand for access to the enzyme. This type of inhibitor displays competitive inhibition. Competitive inhibition can be overcome by adding excessive amounts of substrate. If the amount of substrate greatly out-measures the amount of inhibitor, then the substrate will still bind the enzyme very frequently and allow the reaction to proceed.
Noncompetitive inhibitors bind an enzyme at a spot that is not the active site. Uncompetitive inhibitors bind the enzyme-substrate complex, once the substrate has already entered the active site. Suicide inhibitors "kill" enzymes, typically by making permanent modifications to amino acids in the active site.
A researcher has designed a new type of inhibitor that binds at the active site of an enzyme. What type of inhibition does this molecule display?
Competitive inhibition
Noncompetitive inhibition
Uncompetitive inhibition
Suicide inhibition
Explanation
Because the inhibitor binds at the active site, it is actively competing with the ligand for access to the enzyme. This type of inhibitor displays competitive inhibition. Competitive inhibition can be overcome by adding excessive amounts of substrate. If the amount of substrate greatly out-measures the amount of inhibitor, then the substrate will still bind the enzyme very frequently and allow the reaction to proceed.
Noncompetitive inhibitors bind an enzyme at a spot that is not the active site. Uncompetitive inhibitors bind the enzyme-substrate complex, once the substrate has already entered the active site. Suicide inhibitors "kill" enzymes, typically by making permanent modifications to amino acids in the active site.