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Example Questions
Example Question #11 : Enzymes
Which of the following statements is not true concerning enzymes?
They increase the rate of a reaction
They increase the amount of products
They are biological catalysts
They lower the energy of activation
They increase the amount of products
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 #12 : Enzymes
Which of the following is not a function of an enzyme?
Shift the equilibrium between products and reactants
Accelerate the rate of a process
Lower the energy of the transition state
Lower the activation energy of a reaction
Speed up biological processes
Shift the equilibrium between products and reactants
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 #13 : Enzymes
At what pH does pepsin best function?
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 #14 : Enzymes
What is the active site of an enzyme?
The active site is the portion of the enzyme that engulfs bacteria and other foreign particles in the cell
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 substrate that the enzyme binds to, initiating a chemical reaction
The active site is the portion of the enzyme that substrates bind to, initiating a chemical reaction
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
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 #15 : Enzymes
How do enzymes speed up a chemical reaction?
They increase the temperature of the reaction, allowing it to occur faster
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 shift the equilibrium in favor of the products, allowing more product to be created
They lower the activation energy of a reaction
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 #16 : Enzymes
Which of the following are false regarding enzymes?
Enzymes are biological catalysts which do not require other molecules to perform their function
Enzyme activity is affected by changes in pH and temperature
The binding of a substrate will change an enzyme's shape
Isozymes are a class of enzymes
Enzymatic activity is regulated
Enzymes are biological catalysts which do not require other molecules to perform their function
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 #17 : Enzymes
Which of the following factors affects enzyme activity?
pH
All of these
Substrate Concentration
Enzyme Concentration
Temperature
All of these
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 #18 : 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?
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 #19 : Enzymes
A catalyst is responsible for a decrease in __________ of a reaction.
deactivation energy
substrate complex
None of these
hydrogen bonding
activation energy
activation energy
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 #20 : Enzymes
Which of the following best describes the action of an enzyme?
All of these
They represent the product of a reaction
Slows down reactions so in order to obtain more prducts from the substrate
Catalyze reactions by lowering energy of activation
Catalyze reactions by lowering energy of activation
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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