High School Biology : Understanding Enzymes

Study concepts, example questions & explanations for High School Biology

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Example Questions

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Example Question #1 : Understanding Enzymes

Which of the following statements is not true concerning enzymes?

Possible Answers:

They increase the amount of products

They increase the rate of a reaction

They lower the energy of activation

They are biological catalysts

Correct answer:

They increase the amount of products

Explanation:

Enzymes are biological catalysts that increase the rate of a chemical reaction. This is accomplished by lowering the activation energy for the reaction. Enzymes increase the rate of a reaction, but do NOT increase the amount of products formed in the reaction. They simply cause the products to be formed faster.

Example Question #2 : Understanding Enzymes

Which of the following is not a function of an enzyme?

Possible Answers:

Lower the energy of the transition state

Accelerate the rate of a process

Speed up biological processes

Shift the equilibrium between products and reactants

Lower the activation energy of a reaction

Correct answer:

Shift the equilibrium between products and reactants

Explanation:

A catalyst speeds up the rate of a reaction by lowering the activation energy, which is caused by the high energy transition state. Enzymes are a class of catalyst specific to biological processes, accelerating these processes by lowering activation energy and transition state energy. Catalysts and enzymes may help reactions move faster, but they do not affect the final equilibrium amounts of reactants and products.

Example Question #3 : Protein Function

At what pH does pepsin best function?

Possible Answers:

Correct answer:

Explanation:

Pepsin is an enzyme in the stomach that digests proteins. Because it is active in the stomach, which is highly acidic, pepsin best functions at a low pH between 2 and 2.5.

Pepsinogen is secreted by chief cells and converted into active pepsin after catalyzation by hydrochloric acid. The acid is secreted by parietal cells in response to gastrin secretion by G cells. After the stomach contents enter the duodenum of the small intestine, the acid is neutralized by bicarbonate secretions from the pancreas. This prevents the acid from damaging the walls of the small intestine.

Example Question #2 : Protein Function

What is the active site of an enzyme? 

Possible Answers:

The active site is the portion of the substrate that the enzyme binds to, initiating a chemical reaction

The active site is the portion of the enzyme that DNA binds to, initiating a chemical reaction

The active site is the portion of the enzyme that engulfs bacteria and other foreign particles in the cell

The active site is a portion of the enzyme that allows the enzyme to diffuse through the plasma membrane, allowing it to exit the cell

The active site is the portion of the enzyme that substrates bind to, initiating a chemical reaction

Correct answer:

The active site is the portion of the enzyme that substrates bind to, initiating a chemical reaction

Explanation:

Catalysts are molecules that are capable of increasing reaction speed. Enzymes are a particular subset of catalysts; enzymes are proteins that can aid in biological reactions and are crucial to many metabolic processes that occur in cells. Enzymes lower the activation energy of a given reaction, allowing the reaction to proceed faster. The active site of an enzyme is the region of the enzyme that can bind a substrate, when a substrate collides into the enzyme molecule. Joining of an enzyme and substrate results in a chemical reaction whereby the substrates are converted into products. The active site of an enzyme is specific to the substrate's shape, like a lock-and-key mechanism.

Example Question #3 : Understanding Enzymes

How do enzymes speed up a chemical reaction?

Possible Answers:

They shift the equilibrium in favor of the products, allowing more product to be created

They increase the concentration of one or more of the reactants

They lower the activation energy of a reaction

They tightly bind to the transition state, speeding up the reaction by removing transition states and leaving only products

They increae the temperature of the reaction, allowing it to occur faster

Correct answer:

They lower the activation energy of a reaction

Explanation:

Enzymes work by lowering the activation energy of a reaction, which can occur either by bringing reactants closer together or by destabilizing the transition state. They do not affect the equilibirum of the reaction, meaning they do not affect the amount of reactants or products. They simply increase the speed at which products can be formed by reducing the amount of energy needed to power the reaction.

Example Question #6 : Protein Function

Which of the following are false regarding enzymes?

Possible Answers:

Enzyme activity is affected by changes in pH and temperature

Enzymatic activity is regulated

Enzymes are biological catalysts which do not require other molecules to perform their function

The binding of a substrate will change an enzyme's shape

Isozymes are a class of enzymes

Correct answer:

Enzymes are biological catalysts which do not require other molecules to perform their function

Explanation:

Enzymes are biological catalysts that bind to specific substrates. Enzyme activity is tightly regulated by activators and/or inhibitors. Enzymes will change shape as a result in an induced fit when bound to their substrates, activators, and/or inhibitors. Since enzymes are proteins, environmental changes will affect their activity. For example, high temperatures will denature the protein, rendering the enzyme inactive. Isozymes are a group of enzymes that do not have the exact same amino acid sequence, yet they catalyze the same reactions. Enzymes need cofactors, such as prosthetic groups and/or coenzymes in order to function properly. The precursors to coenzymes are vitamins in the diet.

Example Question #4 : Understanding Enzymes

Which of the following factors affects enzyme activity?

Possible Answers:

Enzyme Concentration 

Temperature

pH

Substrate Concentration

All of these

Correct answer:

All of these

Explanation:

Temperature and pH can affect enzyme activity because they may alter the shape and effectiveness of the enzyme through protein denaturation. Likewise, the availability of reactants and substrates controls the amount of product that the enzyme can catalyze during the reaction. If they are present in low concentrations, then they will inhibit the enzyme’s activity.

Example Question #5 : Understanding Enzymes

The digestive enzyme pepsin is found in the stomach of many mammals, and functions as a digestive enzyme. What pH would a scientist expect pepsin to possess at its most active state?

Possible Answers:

Correct answer:

Explanation:

The stomach is an acidic environment; therefore, one would expect pepsin to be most active at an acidic pH. The answer choice “2” is the most acidic pH. It is also the pH that is generally found in the stomach. Although a pH of 6 is slightly acidic, it is not the pH found in the stomach.

Example Question #6 : Understanding Enzymes

A catalyst is responsible for a decrease in __________ of a reaction.

Possible Answers:

None of these

activation energy

hydrogen bonding

substrate complex

deactivation energy

Correct answer:

activation energy

Explanation:

A catalyst is responsible for a decrease in activation energy of a reaction. This allows an enzyme to use less energy to manipulate its substrate into a transition state.

Example Question #2 : Protein Function

Which of the following best describes the action of an enzyme?

Possible Answers:

They represent the product of a reaction

Catalyze reactions by lowering energy of activation

Slows down reactions so in order to obtain more prducts from the substrate

All of these

Correct answer:

Catalyze reactions by lowering energy of activation

Explanation:

Enzymes are biological molecules that help catalyze reactions by lowering the energy of activation and increasing the rate of a reaction. They can do this by a number of mechanisms including: providing a template for substrates to join together in an efficient manner; distorting a substrate so it approaches the unstable/transition state; and providing a microenvironment conducive to a reaction. Inhibitors and activators can affect enzymes activity by slowing down and increasing enzyme activity respectively.

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