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Which of the following inhibitors will block the active site of a protein?
Proteins can be inhibited in numerous ways by different types of inhibitors. Competitive inhibitors will compete with substrate for the active site to block the protein from performing its function. If there is enough substrate and very little competitive inhibitor, proteins will perform their functions almost as if there were no competitive inhibitors.
In contrast, allosteric inhibitors bind to regions of the protein away from the active site, but change the shape of the active site such that substrate cannot bind. Since there is no direct competition, increasing substrate concentration cannot overcome allosteric inhibition. Non-competitive inhibition is a type of allosteric inhibition. Uncompetitive inhibition occurs when the inhibitor will only bind to the enzyme-substrate complex, locking the substrate in place and preventing other substrates from binding.
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The active site of a protein works in a way similar to __________.
The active site on a protein is the area where a substrate can attach. This relationship is most often described using a metaphor of a lock and a key because each protein has an active site specific to one substrate much like a lock can only be opened by one key.
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__________ modification of an enzyme permits an effector molecule to bind the enzyme at a site other than the active site. This can modulate the enzyme's activity to make it either more or less active.
The key here is to know that if something binds the enzyme at a location other than the active site, the type of modification is defined as allosteric. The other words more generally describe things that can bind to receptors, enzymes, etc., but the best and most specific answer is "allosteric."
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Which of the following best describes why an enzyme loses its catalytic capabilities when exposed to extremely high temperatures?
It is important to know that when exposed to high temperatures, all proteins become denatured, and lose their native shape/conformation.
This has nothing to do with the activation energy of the reaction (eliminating that answer). While some substrates may be degraded at high temperatures, the word "all" renders this answer incorrect, nor does this describe what happens to the enzyme. Covalent modificatinos can change enzymatic function, but do not have anything to do with higher temperature.
The correct answer is that the enzyme itself is denatured, thus changing the shape and the way the active site is shaped, resulting in an inability to efficiently bind its substrate. The structure of the enzyme is dictated by intermolecular forces, which are susceptible to interference from temperature changes (unlike covalent bonds).
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Which mode of enzyme inhibition involves an inhibitor molecule binding the active site of the enzyme?
Competitive inhibition is the only type of inhibition in which the inhibitor molecule directly binds the active site of the enzyme, thereby 'competing' with the actual substrate for location on the enzyme. The other choices involve binding elsewhere on the enzyme (non-competitive) or binding the enzyme-substrate complex but not an isolated enzyme (mixed), but none of them describe binding the active site except for competitive.
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Which of the following statements is not true concerning enzymes?
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.
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Which of the following is not a function of an enzyme?
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.
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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.
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What is the active site of an enzyme?
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.
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How do enzymes speed up a chemical 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.
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Which of the following are false regarding enzymes?
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.
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Which of the following factors affects enzyme activity?
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.
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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.
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A catalyst is responsible for a decrease in __________ of a reaction.
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.
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Which of the following best describes the action of an enzyme?
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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Which of the following does not affect the activity of enzymes?
Enzyme activity can be affected by environmental factors such as temperature and pH. This is because proteins denature and lose their shape at high temperatures and extreme pHs. Most enzymes prefer to act under a temperature close to body temperature. Optimal pH is usually physiologic at pH 6 to 8; however, digestive enzymes prefer lower pH around 2 to 3 (e.g. pepsin, which makes sense because pepsin works in acidic conditions within the stomach).
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Which of the following is true about enzymes?
Enzymes are all proteins, however there are some RNA molecules that have been found to catalyze reactions, but they are termed ribozymes, not enzymes. They speed up reactions by lowering the activation energy of a reaction and do not change the energy states of the reactants or products.
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Which of the following statements is true concerning competitive inhibitors?
A competitive inhibitor will temporarily bind to the active site on an enzyme. This forbids substrates from entering the enzyme's active site and stops the enzyme from catalyzing the reaction.
In contrast, non-competitive inhibitors will bind to other regions of the enzyme, outside of the active site, and cause the active site to change shape. This change then prevents substrates from binding.
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What inhibitor type prevents catalysis by noncovalently binding to an enzyme's active site?
Inhibitors are able to prevent maximum enzymatic rates in a variety of ways. Some inhibitors, like noncompetive inhibitors, are able to attach at a point on the enzyme and alter its conformation. Competitive inhibitors, however, bind directly at the active site, which prevents substrate from entering the enzyme.
Competitive inhibitors are the only inhibitor type to bind directly to the enzyme actve site.
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Some enzymes have a direct function of catalyzing a reaction within a cell. Other enzymes simply change their fellow enzymes.
Enzyme X is found in a certain cell and is normally active. At a certain point, the cell creates enzyme X inhibitor, which inhibits enzyme X. What can be concluded about the cell following the synthesis of the inhibitor?
An inhibitor binds to an enzyme and stops it from performing its normal function. It does not destroy the enzyme and does not change the amount present, but it decreases the amount of activity of that enzyme.
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