Biology Mastering chapter 6

A(n) _____ reaction occurs spontaneously. anabolic exergonic kinetic chemical endergonic

B

In general, enzymes are what kinds of molecules? lipids nucleic acids carbohydrates proteins minerals

proteins

What name is given to the reactants in an enzymatically catalyzed reaction? substrate EA products active sites reactors

substrate

Which of the following statements about the role of ATP in cell metabolism is true? The energy from the hydrolysis of ATP may be directly coupled to endergonic processes by the transfer of the phosphate group to another molecule. The free energy released by ATP hydrolysis has a much more negative ΔG value than the hydrolysis of phosphate groups from other phosphorylated molecules. The phosphate bonds of ATP are unusually strong bonds.

A A key feature in the way cells manage their energy resources to do this work is energy coupling, the use of an exergonic process to drive an endergonic one. ATP is responsible for mediating most energy coupling in cells, and in most cases it acts as the immediate source of energy that powers cellular work. Read about energy coupling.

Select the correct statement about chemical energy, a term used by biologists to refer to potential energy available for release in a chemical reaction. When a glucose molecule is catabolized to CO2 and H2O, chemical energy is lost. Light energy is converted to chemical energy during photosynthesis. A photosynthetic cell within a plant leaf produces chemical energy, stored within glucose molecules.

B: Photosynthetic cells capture light energy and transform some of it to chemical energy as they synthesize glucose from CO2 and H2O. Read about the laws of energy transformation.

What is the free energy change (ΔG) of the hydrolysis of ATP to ADP? The free-energy change (ΔG) of the hydrolysis of ATP to ADP and Pi is constant at -7.3 kcal/mole. The free-energy change (ΔG) of the hydrolysis of ATP to ADP and Pi is approximately -7.3 kcal/mole, but it varies from species to species. The free-energy change (ΔG) of the hydrolysis of ATP to ADP and Pi may vary considerably with variations in pH, temperature, atmospheric pressure, and concentrations of reactants and products.

C The free-energy change (ΔG) of the hydrolysis of ATP to ADP and Pi is -7.3 kcal/mole under standard conditions. Standard conditions are defined as a temperature of 298 K (or 250C), 1 atm, pH 7, and equal 1M concentrations present of all reactants and products. In living cells, conditions do not conform to standard conditions, primarily because reactant and product concentrations differ from 1 M. For example, when ATP hydrolysis occurs under cellular conditions, the actual ΔG is about -13 kcal/mol, 78% greater than the energy released by ATP hydrolysis under standard conditions.

An enzyme _____. can bind to nearly any molecule is a inorganic catalyst is a source of energy for endergonic reactions is an organic catalyst increases the EA of a reaction

D

The energy for an endergonic reaction comes from a(n) _____ reaction. anabolic ADP + P --> ATP synthesis exergonic glucose + glucose --> maltose

D

Enzymes are described as catalysts, which means that they __________. View Available Hint(s) are proteins increase the free energy of the reactants to make the reaction go faster can alter the free energy change (ΔG) for a chemical reaction increase the rate of a reaction without being consumed by the reaction provide activation energy for the reactions they facilitate

D Increasing the rate of reaction without being consumed permits enzyme molecules to be used repeatedly.

The following reaction A --> B + C + heat is a(n) _____ reaction. exchange dehydration synthesis anabolic endergonic exergonic

E

Which of the following is NOT a way in which an enzyme can speed up the reaction that it catalyzes? View Available Hint(s) The binding of two substrates in the active site provides the correct orientation for them to react to form a product. Binding of the substrate to the active site can stretch bonds in the substrate that need to be broken. The enzyme binds a cofactor that interacts with the substrate to facilitate the reaction. The active site of the enzyme can provide a microenvironment with a different pH that facilitates the reaction. The active site can provide heat from the environment that raises the energy content of the substrate.

E: An enzyme cannot extract heat from the environment to speed a reaction. It can only lower the activation energy barrier so that more substrates have the energy to react.

What is energy coupling? the use of energy released from an exergonic reaction to drive an endergonic reaction a barrier to the initiation of a reaction a description of the energetic relationship between the reactants and products in an exergonic reaction the hydrolysis of ATP to ADP + P the use of an enzyme to reduce EA

A

Which of these are by-products of cellular respiration? heat, carbon dioxide, and water carbon dioxide and water glucose, carbon dioxide, and water ATP, carbon dioxide, and water ATP and carbon dioxide

A

1. A (n)_______ inhibitor has a structure that is so similar to the substrate that it can bond to the enzyme just like the substrate. 2. A (n)_________ inhibitor binds to a site on the enzyme that is not the active site. 3. Usually, a(n) ________ inhibitor forms a covalent bond with an amino acid side group within the active site, which prevents the substrate from entering the active site or prevents catalytic activity. 4. The competitive inhibitor competes with the substrate for the _________ on the enzyme. 5. When the noncompetitive inhibitor is bonded to the _________, the shape of the enzyme is distorted. 6. Enzyme inhibitors disrupt normal interactions between an enzyme and its _________.

1. A (n)competitive inhibitor has a structure that is so similar to the substrate that it can bond to the enzyme just like the substrate. 2. A (n)noncompetitive inhibitor binds to a site on the enzyme that is not the active site. 3. Usually, a(n) irreversible inhibitor forms a covalent bond with an amino acid side group within the active site, which prevents the substrate from entering the active site or prevents catalytic activity. 4. The competitive inhibitor competes with the substrate for the active site on the enzyme. 5. When the noncompetitive inhibitor is bonded to the enzyme, the shape of the enzyme is distorted. 6. Enzyme inhibitors disrupt normal interactions between an enzyme and its substrate. Competitive inhibitors compete physically and structurally with the substrate for an enzyme's active site; they can be outcompeted by adding extra substrate. Noncompetitive inhibitors do not compete for the active site, but inhibit the enzyme by binding elsewhere and changing the enzyme's shape. Irreversible inhibitors bind directly to the active site by covalent bonds, which change the structure of the enzyme and inactivate it permanently. Most medications are enzyme inhibitors of one kind or another.

1. An enzyme is _________when it loses its native conformation and its biological activity. 2. An enzyme is considered a _________because it speeds up chemical reactions without being used up. 3. An enzyme is considered _________because of its ability to recognize the shape of a particular molecule. 4. A _________, such as a vitamin, binds to an enzyme and plays a role in catalysis. 5. When properly aligned, the enzyme and substrate form an enzyme-substrate (ES)___________. 6. A substrate binds to an enzyme at the _________, where the reaction occurs. 7. In a catalyzed reaction a reactant is often called a _______.

1. An enzyme is denaturedwhen it loses its native conformation and its biological activity. 2. An enzyme is considered a catalystbecause it speeds up chemical reactions without being used up. 3. An enzyme is considered specificbecause of its ability to recognize the shape of a particular molecule. 4. A cofactor, such as a vitamin, binds to an enzyme and plays a role in catalysis. 5. When properly aligned, the enzyme and substrate form an enzyme-substrate (ES)complex. 6. A substrate binds to an enzyme at the active site, where the reaction occurs. 7. In a catalyzed reaction a reactant is often called a substrate. A substrate binds at an enzyme's active site; the enzyme typically recognizes the specific shape of its substrate. A cofactor, such as an inorganic ion or vitamin, may bind to the enzyme and assist in catalyzing the reaction. The reaction environment must be appropriate for catalysis to proceed. An enzyme will denature, or change its shape and lose its biological activity, at too high a temperature or at a pH outside the enzyme's optimal range.

Which statement about the binding of enzymes and substrates is correct? When substrate molecules bind to the active site of the enzyme, the enzyme undergoes a slight change in shape. Substrate molecules fit into the active site of an enzyme like a key fits into a lock. Substrate molecules bind to the active site of the enzyme only by weak bonds, such as hydrogen bonds or hydrophobic attraction.

A As the substrate enters the active site, the enzyme changes shape slightly due to interactions between the substrate's chemical groups and chemical groups on the side chains of the amino acids that form the active site. This shape change makes the active site fit even more snugly around the substrate. This induced fit is like a clasping handshake.

Which of the following statements about ATP (adenosine triphosphate) is correct? View Available Hint(s) The cycling between ATP and ADP + Pi provides an energy coupling between catabolic and anabolic pathways. The hydrolysis of ATP is an endergonic process. The energy release on hydrolysis of ATP is the result of breaking a high-energy bond. The hydrolysis of ATP can supply energy needed for catabolic pathways. Almost all of the free energy released on the hydrolysis of ATP is released as heat.

A Catabolic pathways provide the energy needed to make ATP from ADP and Pi. The hydrolysis of ATP to ADP + Pi releases the same amount of energy.

In cells, what is usually the immediate source of energy for an endergonic reaction? ADP ATP as spontaneous reactions, endergonic reactions do not need an addition of energy glucose sugar

B

The process of cellular respiration, which converts simple sugars such as glucose into CO2 and water, is an example of __________. View Available Hint(s) a pathway in which the entropy of the system decreases a catabolic pathway a pathway that converts organic matter into energy an endergonic pathway a pathway that occurs in animal cells but not plant cells

B

The reaction ADP + P --> ATP is a(n) _____ reaction. hydrolysis endergonic spontaneous chemical exergonic

B

You have added an irreversible inhibitor to a sample of enzyme and substrate. At this point, the reaction has stopped completely. What can you do to regain the activity of the enzyme? View Available Hint(s) Removing the irreversible inhibitor should get the reaction working again. The enzyme is inactive at this point. New enzyme must be added to regain enzyme activity. Adding more substrate will increase the rate of reaction. Adding more inhibitor should get the reaction up to speed again.

B Because they bind directly to the active site by covalent bonds, irreversible inhibitors permanently render an enzyme inactive. Some drugs are irreversible inhibitors, including the antibiotic penicillin (which inhibits an enzyme involved in bacterial cell-wall synthesis) and aspirin (which inhibits cyclooxygenase-2, the enzyme involved in the inflammatory reaction).

What is the fate of the phosphate group that is removed when ATP is converted to ADP? It is used to convert an ATP into an AQP. It is acquired by a reactant in an endergonic reaction. It is acquired by a reactant in a spontaneous reaction. It is acquired by a reactant in an exergonic reaction. It is broken down into one phosphorus and four oxygen atoms.

B By acquiring the phosphate group the reactant acquires energy.

You have an enzymatic reaction proceeding at the optimum pH and optimum temperature. You add a competitive inhibitor to the reaction and notice that the reaction slows down. What can you do to speed the reaction up again? Add more inhibitor to speed up the reaction. Add more substrate; it will outcompete the inhibitor and increase the reaction rate. Increase the temperature. Increase the pH.

B Competitive inhibition can be overcome by adding more substrate to outcompete the inhibitor. Many drugs used to treat different medical conditions, including hypertension, are competitive inhibitors. It is fairly easy to make a molecule that is similar in structure to a particular substrate because the known enzyme's shape can be used as a model of what the molecule needs to look like. It is more difficult to make a noncompetitive inhibitor because it is less obvious what the noncompetitive inhibitor's shape and structure should be.

Which of these reactions requires a net input of energy from its surroundings? catabolic exergonic endergonic ATP --> ADP + P hydrolysis

C

- where is the reaction rate constant - In which region is the enzyme saturated with substrate? - Consider a situation in which the enzyme is operating at optimum temperature and pH, and has been saturated with substrate. What is your best option for increasing the rate of the reaction? Increase the pH. Increase the temperature. Increase the enzyme concentration. Increase the substrate concentration.

C C Increase enzyme con.If an enzyme is saturated with substrate, and it is operating at optimum pH and optimum temperature, there is very little that can be done except to increase the enzyme concentration. Some enzymes can be activated further by allosteric activators, in which case one might add some activator to the reaction. But otherwise, increasing the enzyme concentration is the only option.

Which of the following statements about the combustion of glucose with oxygen to form water and carbon dioxide (C6H12O6 + 6 O2 → 6 CO2 + 6 H2O) is correct? View Available Hint(s) This is the process of cellular respiration, an anabolic pathway that releases free energy. The entropy of the universe decreases as the result of this reaction. The free energy lost in this combustion is less than the energy that appears as heat. The reverse reaction, making glucose from water and carbon dioxide, must be an exergonic reaction. The entropy of the products is greater than the entropy of the reactants.

E: A large molecule (glucose) has been converted into several smaller molecules (water and carbon dioxide); thus, the products have more disorder (greater entropy) than the reactants.

In your body, what process converts the chemical energy found in glucose into the chemical energy found in ATP? potentiation anabolism digestion cellular respiration redox

cellular respiration

low/high reaction rate uncatalyzed reaction catalyzed enzyme

lowest reaction rate uncatalyzed reaction catalyzed by enzyme A catalyzed by enzyme B Highest reaction rate Enzymes lower the activation energy of a chemical reaction. This means that a catalyzed reaction is more likely to proceed than an uncatalyzed reaction, and it forms products more rapidly than an uncatalyzed reaction.

As a result of its involvement in a reaction, an enzyme _____. is used up loses a phosphate group is unchanged loses energy permanently alters its shape.

unchanged