AP Biology : Enzymes

Study concepts, example questions & explanations for AP Biology

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Example Questions

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Example Question #1 : Enzymes

Which of the following is true regarding competitive and noncompetitive inhibition?

   I. Both can be overcome by increasing the substrate concentration

   II. Competitive inhibition induces changes to the active site

   III. Noncompetitive inhibition has no effect on the enzyme affinity for substrates

Possible Answers:

II only

I only

II and III

III only

Correct answer:

III only

Explanation:

Statement I is false because increasing the substrate concentration will only help overcome competitive inhibition. Noncompetitive inhibition can only be overcome if the inhibitor is removed from the enzyme.

Statement II is also false because competitive inhibitors do not change the active site. They bind to the active site and prevent substrates from binding. Noncompetitive inhibitors bind elsewhere on the enzyme and alter the shape of the active site, thereby preventing substrate binding.

Statement III is true because noncompetitive inhibition does not affect the enzyme affinity for substrates. The enzyme still has the same affinity, but the substrates can’t bind because of the altered active site.

Example Question #2171 : Ap Biology

An antibiotic binds an enzyme, causing it to produce substrate C of a metabolic pathway instead of substrate A of the same pathway. Substrate C ultimately inhibits the enzyme in the normal course of the pathway.

In this metabolic pathway, Substrate C is acting as a(n) __________.

Possible Answers:

negative feedback inhibitor

competitive inhibitor

noncompetitive inhibitor

transcription factor

nucleic acid

Correct answer:

negative feedback inhibitor

Explanation:

Negative feedback interrupts a metabolic pathways by producing a substrate that inhibits enzymes in the beginning steps of the metabolic cycle. If a chemical is "mimicking" substrate C  or causing Substrate C to be produced before other steps in a cycle, the enzyme is inhibited by the excess of substrate C thus the pathway can not continue. Most such molecules are proteins that interact with enzymes. 

Example Question #2172 : Ap Biology

Substrates formed downstream in a metabolic pathway that act to increase the progression of that metabolic pathway are said to exhibit a __________ mechanism.

Possible Answers:

hormonal

positive feedback

competitive inhibition

negative feedback

noncompetitive inhibition

Correct answer:

positive feedback

Explanation:

A substrate that acts as a "positive motivator" of, or to enhance a metabolic pathway, is also known as a positive feedback regulator or a substance that has a positive feedback mechanism.

Example Question #1 : Enzymes

If an antibiotic binds the active site of an enzyme but does not change the structure of that enzyme, once removed, the enzyme returns to normal function. In this case, the antibiotic is acting via what enzyme interaction?

Possible Answers:

Positive feedback

Noncompetitive inhibition

Competitive inhibition

Negative feedback

Denaturation

Correct answer:

Competitive inhibition

Explanation:

Competitive inhibition occurs when an substrate or inhibitor compete with the normal substrate for binding the active sight of an enzyme. The proper functioning of the enzyme depends on the concentration ratio of inhibitor to enzyme or substrate to enzyme. The competitive inhibition of the enzyme in this case by the antibiotic has potentially bactericidal or bacteriostatic effect on the bacteria until that antibiotic concentration decreases. Negative feedback involves the product of a set of metabolic reactions inhibiting the formation of a precursor of that metabolic pathway, thereby decreasing its own production.

Example Question #2 : Understand Competitive And Noncompetitive Inhibition

You are reading about the functions of a unique chemical compound. This compound works on enzymes throughout the body by altering the shape of the enzyme without blocking the active site. This compound functions via which mechanism?

Possible Answers:

Feedback inhibition

Neutral inhibition

Positive inhibition

Competitive inhibition

Noncompetitive inhibition

Correct answer:

Noncompetitive inhibition

Explanation:

Noncompetitive inhibition is a type of enzymatic alteration that results in changes to enzymatic function without alterations to the active site. If the active site was to be blocked, this compound would function via competitive inhibition. The other terms do not describe any type of enzymatic inhibition process in the human body. Be able to distinguish the difference between competitive and noncompetitive inhibition.

Example Question #2173 : Ap Biology

Which of the following factors has an effect on the rate at which enzymes catalyze a reaction?

Possible Answers:

pH of environment

All of these factors have an effect on the rate at which enzymes catalyze a reaction

Concentration of substrate and enzyme

Temperature of environment

Correct answer:

All of these factors have an effect on the rate at which enzymes catalyze a reaction

Explanation:

The temperature and pH of the environment, as well as the concentration of the substrate and enzyme, all affect the rate at which an enzyme catalyzes a reaction. As a result, enzymes have optimal conditions in which they can work at peak efficiency.

Example Question #2 : Understand The Effect Of Environment Of The Enzyme

Consider the reaction:

This reaction is catalyzed by an enzyme called carbonic anhydrase. Which of the following will result from increasing the concentration of carbonic anhydrase?

Possible Answers:

It will increase the equilibrium constant

It will cause reaction to go slower

It will have no effect on the equilibrium constant

It will decrease the equilibrium constant

Correct answer:

It will have no effect on the equilibrium constant

Explanation:

Enzymes are catalysts that help a reaction proceed faster. Increasing the concentration of carbonic anhydrase will not cause the reaction to go slower. Recall that catalysts (in this case carbonic anhydrase) do not alter the equilibrium of a reaction. They simply speed up the process so that equilibrium can be achieved more quickly. Increasing or decreasing the equilibrium constant means that there is a change in the equilibrium state of the reaction.

The equilibrium constant can only be affected by temperature changes or pressure changes, if there is a gas involved in the reaction. Catalysts affect the rate constant, which is dependent on activation energy. By decreasing activation energy, catalysts can increase the rate constant and allow a reaction to proceed faster.

Example Question #4 : Enzymes

In non-physiological reactions an increase in temperature will increase the reaction rate; however, in physiological reactions there is an optimum temperature at which an enzyme operates. Increasing the temperature beyond this will not increase enzyme activity or reaction rate. What explains this phenomenon?

Possible Answers:

Heat will shift the equilibrium to the left, favoring the reactant side

High temperatures will change the shape and functionality of proteins

Increasing the temperature will decrease the activation energy

Increasing the temperature will increase the activation energy

Correct answer:

High temperatures will change the shape and functionality of proteins

Explanation:

There is an optimum temperature at which an enzyme is most effective. Decreasing or increasing the temperature from the optimum will lead to denaturation of proteins, which will affect their functionality. Most protein structure is dependent on non-covalent intermolecular forces, such as hydrogen bonding and hydrophobic interactions. Heat can disrupt these forces, causing the protein to lose its structure, which leads to a loss of functionality.

You can eliminate the answer choices about activation energy because changing temperature will have no effect on the activation energy. Adding heat could shift the equilibrium to the right or left, depending on whether the reaction is exothermic or endothermic.

Example Question #2 : Enzymes

Which of the following characteristics affects the function of an enzyme?

Possible Answers:

pH

All of these

None of these

Substrate concentration

Temperature

Correct answer:

All of these

Explanation:

Temperature, pH, and substrate concentration all affect the function of an enzyme; therefore, the correct answer is all of these.

Example Question #1 : Understand The Effect Of Environment Of The Enzyme

Which of the following statements about enzymes is correct?

Possible Answers:

They are polymers of carbohydrates

They always require a coenzyme

They are consumed in the reaction

They function under a narrow pH range

They are used to create ATP

Correct answer:

They function under a narrow pH range

Explanation:

The correct answer to this question is they function under a narrow pH range.

Enzymes do indeed function under a narrow pH range. A narrow pH range is needed because enzymes speed up reactions by lowering the activation energy and in order to do this very specific conditions must be met. Coenzymes are not always needed and they are certainly not consumed in a reaction. Enzymes also are proteins so they are polymers of amino acids, not carbohydrates. Also enzymes have no part in the creation of ATP.

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