Cellular Energetics Practice Quiz 1
Quiz over AP Biology Unit 3: Cellular Energetics (Cell Respiration and Photosynthesis)
- 1.
Which of the following describe(s) some aspect of metabolism?
- A.
Synthesis of macromoleculessynthesis of macromolecules
- B.
Breakdown of macromolecules
- C.
Control of enzyme activity
- D.
A and B only
- E.
A, B, and C
Correct Answer
E. A, B, and CExplanation
The correct answer is A, B, and C. This is because metabolism involves the synthesis of macromolecules, the breakdown of macromolecules, and the control of enzyme activity. These processes are essential for the functioning and regulation of biological systems.Rate this question:
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- 2.
Which term most precisely describes the cellular process of breaking down large molecules into smaller ones?
- A.
Catalysis
- B.
Metabolism
- C.
Anabolism
- D.
Dehydration
- E.
Catabolism
Correct Answer
E. CatabolismExplanation
Catabolism is the correct answer because it refers to the cellular process of breaking down large molecules into smaller ones. This process involves the release of energy and the breakdown of complex molecules into simpler ones. It is the opposite of anabolism, which is the process of building up complex molecules from simpler ones. Catalysis refers to the process of speeding up a chemical reaction, while dehydration is the process of removing water molecules. Therefore, catabolism is the most precise term to describe the given cellular process.Rate this question:
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- 3.
Which of the following statements correctly describe(s) catabolic pathways?
- A.
They do not depend on enzymes.
- B.
They consume energy to build up polymers from monomers.
- C.
They release energy as they degrade polymers to monomers.
- D.
They lead to the synthesis of catabolic compounds.
- E.
Both A and B
Correct Answer
C. They release energy as they degrade polymers to monomers.Explanation
Catabolic pathways are metabolic processes that involve the breakdown of complex molecules into simpler ones. These pathways rely on enzymes to catalyze the chemical reactions involved in the breakdown process. They release energy as they degrade polymers to monomers, which can be used by the cell for various purposes. Therefore, the correct answer is "They release energy as they degrade polymers to monomers."Rate this question:
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- 4.
Which of the following is (are) true for anabolic pathways?
- A.
They do not depend on enzymes.
- B.
They are highly regulated sequences of chemical reactions.
- C.
They consume energy to build up polymers from monomers.
- D.
They release energy as they degrade polymers to monomers.
- E.
Both B and C
Correct Answer
E. Both B and CExplanation
Anabolic pathways are highly regulated sequences of chemical reactions that consume energy to build up polymers from monomers. This means that both statement B, which states that anabolic pathways are highly regulated sequences of chemical reactions, and statement C, which states that anabolic pathways consume energy to build up polymers from monomers, are true.Rate this question:
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- 5.
What is the term for metabolic pathways that release stored energy by breaking down complex molecules?
- A.
Anabolic pathways
- B.
Catabolic pathways
- C.
Fermentation pathways
- D.
Thermodynamic pathways
- E.
Bioenergetic pathways
Correct Answer
B. Catabolic pathwaysExplanation
Catabolic pathways are the correct answer because they refer to metabolic processes that break down complex molecules to release stored energy. These pathways involve the breakdown of larger molecules into smaller ones, such as the breakdown of carbohydrates, lipids, and proteins through processes like glycolysis, beta oxidation, and protein degradation. This release of energy is essential for various cellular activities and is a fundamental aspect of metabolism. Anabolic pathways, on the other hand, are metabolic processes that build complex molecules from simpler ones, requiring energy input.Rate this question:
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- 6.
What is the term used for the metabolic pathway in which glucose (C6H12O6) is degraded to carbon dioxide (CO2) and water?
- A.
Cellular respiration
- B.
Glycolysis
- C.
Fermentation
- D.
Citric acid cycle
- E.
Oxidative phosphorylation
Correct Answer
A. Cellular respirationExplanation
Cellular respiration is the correct answer because it refers to the metabolic pathway in which glucose is broken down into carbon dioxide and water. This process occurs in the mitochondria of cells and is essential for the production of ATP, the main energy currency of the cell. Glycolysis, fermentation, citric acid cycle, and oxidative phosphorylation are all steps or components of cellular respiration, but cellular respiration encompasses the entire process of glucose degradation to CO2 and water.Rate this question:
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- 7.
Which of the following statements concerning the metabolic degradation of glucose (C6H12O6) to carbon dioxide (CO2) and water is (are) true?
- A.
The breakdown of glucose to carbon dioxide and water is exergonic.
- B.
The breakdown of glucose to carbon dioxide and water has a free energy change of -686 kcal/mol.
- C.
LivThe breakdown of glucose to carbon dioxide and water involves oxidation-reduction or redox reactions.
- D.
Only A and B are correct.
- E.
A, B, and C are correct.
Correct Answer
E. A, B, and C are correct.Explanation
The breakdown of glucose to carbon dioxide and water is exergonic, meaning it releases energy. This process has a free energy change of -686 kcal/mol, indicating that it is energetically favorable. Additionally, the breakdown of glucose to carbon dioxide and water involves oxidation-reduction or redox reactions, where glucose is oxidized and carbon dioxide is reduced. Therefore, all statements A, B, and C are correct.Rate this question:
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- 8.
Which of the following statements is (are) correct about an oxidation-reduction (or redox) reaction?
- A.
The molecule that is reduced gains electrons.
- B.
The molecule that is oxidized loses electrons.
- C.
The molecule that is reduced loses electrons.
- D.
The molecule that is oxidized gains electrons.
- E.
Both A and B are correct.
Correct Answer
E. Both A and B are correct.Explanation
In an oxidation-reduction (or redox) reaction, the molecule that is reduced gains electrons, which means it is being reduced. On the other hand, the molecule that is oxidized loses electrons, which means it is being oxidized. Therefore, both statements A and B are correct.Rate this question:
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- 9.
The molecule that functions as the reducing agent (electron donor) in a redox or oxidation-reduction reaction
- A.
Gains electrons and gains energy.
- B.
Loses electrons and loses energy.
- C.
Gains electrons and loses energy.
- D.
Loses electrons and gains energy.
- E.
Neither gains nor loses electrons, but gains or loses energy.
Correct Answer
B. Loses electrons and loses energy.Explanation
In a redox or oxidation-reduction reaction, the reducing agent is the molecule that donates electrons to another molecule. When a molecule loses electrons, it is oxidized and loses energy. Therefore, the correct answer is "loses electrons and loses energy."Rate this question:
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- 10.
Why does the oxidation of organic compounds by molecular oxygen to produce CO2 and water release free energy?
- A.
The covalent bonds in organic molecules are higher energy bonds than those in water and carbon dioxide.
- B.
Electrons are being moved from atoms that have a lower affinity for electrons (such as C) to atoms with a higher affinity for electrons (such as O).
- C.
The oxidation of organic compounds can be used to make ATP.
- D.
The electrons have a higher potential energy when associated with water and CO2 than they do in organic compounds.
- E.
The covalent bond in O2 is unstable and easily broken by electrons from organic molecules.
Correct Answer
B. Electrons are being moved from atoms that have a lower affinity for electrons (such as C) to atoms with a higher affinity for electrons (such as O).Explanation
During the oxidation of organic compounds, electrons are transferred from atoms with a lower affinity for electrons (such as carbon) to atoms with a higher affinity for electrons (such as oxygen). This transfer of electrons releases energy, as the electrons are moving from a lower energy state to a higher energy state. This energy is then released as free energy, which can be used to perform work or drive cellular processes.Rate this question:
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- 11.
Which of the following statements describes the results of this reaction? C6H12O6 + 6 O2 --> 6 CO2 + 6 H2O + Energy
- A.
C6H12O6 is oxidized and O2 is reduced.
- B.
O2 is oxidized and H2O is reduced.
- C.
CO2 is reduced and O2 is oxidized.
- D.
C6H12O6 is reduced and CO2 is oxidized.
- E.
O2 is reduced and CO2 is oxidized.
Correct Answer
A. C6H12O6 is oxidized and O2 is reduced.Explanation
In this reaction, glucose (C6H12O6) is being oxidized, meaning it is losing electrons and becoming more positively charged. Oxygen (O2) is being reduced, meaning it is gaining electrons and becoming more negatively charged. Therefore, the correct answer is that C6H12O6 is oxidized and O2 is reduced.Rate this question:
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- 12.
When a glucose molecule loses a hydrogen atom (not a hydrogen ion) as the result of an oxidation-reduction reaction, the molecule becomes
- A.
Dehydrogenated.
- B.
Hydrogenated.
- C.
Oxidized.
- D.
Reduced.
- E.
An oxidizing agent.
Correct Answer
C. Oxidized.Explanation
When a glucose molecule loses a hydrogen atom as the result of an oxidation-reduction reaction, it means that the glucose molecule has undergone oxidation. Oxidation is the process of losing electrons or gaining oxygen atoms, and in this case, the glucose molecule has lost a hydrogen atom, which is equivalent to losing an electron. Therefore, the correct answer is oxidized.Rate this question:
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- 13.
Which of the following statements about NAD+ is false?
- A.
NAD+ is reduced to NADH during both glycolysis and the citric acid cycle.
- B.
NAD+ has more chemical energy than NADH.
- C.
NAD+ is reduced by the action of dehydrogenases.
- D.
NAD+ can receive electrons for use in oxidative phosphorylation.
- E.
In the absence of NAD+, glycolysis cannot function.
Correct Answer
B. NAD+ has more chemical energy than NADH.Explanation
NAD+ is actually the oxidized form of NADH. During glycolysis and the citric acid cycle, NAD+ is reduced to NADH by accepting electrons. This means that NADH has more chemical energy than NAD+. Therefore, the statement that NAD+ has more chemical energy than NADH is false.Rate this question:
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- 14.
In order for NAD+ to remove electrons from glucose or other organic molecules, which of the following must be true?
- A.
The organic molecule or glucose must be negatively charged in order to reduce the positively charged NAD+.
- B.
Oxygen must be present to oxidize the NADH produced back to NAD+.
- C.
The free energy liberated when electrons are removed from the organic molecules must be greater than the energy required to give the electrons to NAD+.
- D.
A and B are both correct.
- E.
A, B, and C are all correct.
Correct Answer
C. The free energy liberated when electrons are removed from the organic molecules must be greater than the energy required to give the electrons to NAD+.Explanation
For NAD+ to remove electrons from glucose or other organic molecules, the free energy released during this process must be greater than the energy needed to transfer the electrons to NAD+. This is because the transfer of electrons requires energy input, and if the energy released is not greater than the energy required, the reaction will not proceed. Therefore, option C is correct. The other options are incorrect because they do not address the energy requirement for electron transfer.Rate this question:
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- 15.
Where does glycolysis takes place?
- A.
Mitochondrial matrix
- B.
Mitochondrial outer membrane
- C.
Mitochondrial inner membrane
- D.
Mitochondrial intermembrane space
- E.
Cytosol
Correct Answer
E. CytosolExplanation
Glycolysis is a metabolic pathway that occurs in the cytosol of cells. It is the first step in cellular respiration and involves the breakdown of glucose into pyruvate. This process does not require oxygen and is common to both aerobic and anaerobic organisms. The cytosol, which is the liquid component of the cytoplasm, provides the necessary environment and enzymes for glycolysis to take place. Therefore, the correct answer is cytosol.Rate this question:
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- 16.
During glycolysis, when glucose is catabolized to pyruvate, most of the energy of glucose is
- A.
Transferred to ADP, forming ATP.
- B.
Transferred directly to ATP.
- C.
Retained in the pyruvate.
- D.
Stored in the NADH produced.
- E.
Used to phosphorylate fructose to form fructose-6-phosphate.
Correct Answer
C. Retained in the pyruvate.Explanation
During glycolysis, glucose is catabolized to pyruvate. The process involves the breakdown of glucose molecules into two molecules of pyruvate. Most of the energy from glucose is captured and retained in the pyruvate molecules. This energy is stored in the form of high-energy electrons and hydrogen atoms, which are transferred to NAD+ to produce NADH. The NADH molecules carry this energy to the electron transport chain, where it is ultimately used to generate ATP through oxidative phosphorylation. Therefore, the correct answer is retained in the pyruvate.Rate this question:
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- 17.
Why is ATP an important molecule in metabolism?
- A.
Its hydrolysis provides an input of free energy for exergonic reactions.
- B.
It provides energy coupling between exergonic and endergonic reactions.
- C.
Its terminal phosphate group contains a strong covalent bond that when hydrolyzed releases free energy.
- D.
. A and B only
- E.
A, B and C
Correct Answer
B. It provides energy coupling between exergonic and endergonic reactions.Explanation
ATP is an important molecule in metabolism because it provides energy coupling between exergonic and endergonic reactions. This means that ATP can transfer energy from exergonic reactions (reactions that release energy) to endergonic reactions (reactions that require energy). By transferring a phosphate group to another molecule, ATP can provide the necessary energy for the endergonic reaction to occur. This energy transfer allows cells to efficiently use and transfer energy, making ATP crucial for various metabolic processes.Rate this question:
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- 18.
The hydrolysis of ATP to ADP and inorganic phosphate (ATP + H2O --> ADP + Pi )
- A.
Has a G of about -7 kcal/mol under standard conditions.
- B.
Involves hydrolysis of a terminal phosphate bond of ATP.
- C.
Can occur spontaneously under appropriate conditions.
- D.
Only A and B are correct.
- E.
A, B, and C are correct.
Correct Answer
E. A, B, and C are correct.Explanation
The hydrolysis of ATP to ADP and inorganic phosphate has a negative Gibbs free energy (G) value of about -7 kcal/mol under standard conditions, indicating that it is an energetically favorable reaction. This reaction involves the hydrolysis of a terminal phosphate bond of ATP, which releases energy. Additionally, the hydrolysis of ATP can occur spontaneously under appropriate conditions, further supporting the statement that A, B, and C are all correct.Rate this question:
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- 19.
When 10,000 molecules of ATP are hydrolyzed to ADP and Pi in a test tube, about twice as much heat is liberated as when a cell hydrolyzes the same amount of ATP. Which of the following is the best explanation for this observation?
- A.
Cells are open systems, but a test tube is a closed system.
- B.
Cells are less efficient at heat production than nonliving systems.
- C.
The hydrolysis of ATP in a cell produces different chemical products than does the reaction in a test tube.
- D.
The reaction in cells must be catalyzed by enzymes, but the reaction in a test tube does not need enzymes.
- E.
Cells convert some of the energy of ATP hydrolysis into other forms of energy besides heat.
Correct Answer
E. Cells convert some of the energy of ATP hydrolysis into other forms of energy besides heat.Explanation
The answer "Cells convert some of the energy of ATP hydrolysis into other forms of energy besides heat" is the best explanation for the observation that a cell hydrolyzes the same amount of ATP but produces less heat compared to a test tube. This is because cells are highly efficient and can utilize the energy released from ATP hydrolysis for various cellular processes such as mechanical work, active transport, and biosynthesis. In contrast, a test tube lacks the complex machinery and processes present in a cell, resulting in a greater proportion of the energy being released as heat.Rate this question:
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- 20.
ATP generally energizes a cellular process by
- A.
Releasing heat upon hydrolysis.
- B.
Acting as a catalyst.
- C.
Coupling free energy released by ATP hydrolysis to free energy needed by other reactions.
- D.
Breaking a high-energy bond.
- E.
Binding directly to the substrate(s) of the enzyme.
Correct Answer
C. Coupling free energy released by ATP hydrolysis to free energy needed by other reactions.Explanation
ATP is known as the energy currency of the cell because it provides the necessary energy for cellular processes. It achieves this by coupling the free energy released during its hydrolysis (breakdown) to other reactions that require energy. This means that when ATP is hydrolyzed, it releases energy that can be used to drive other reactions in the cell. Therefore, the correct answer is that ATP couples the free energy released by its hydrolysis to the free energy needed by other reactions.Rate this question:
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- 21.
What term is used to describe the transfer of free energy from catabolic pathways to anabolic pathways?
- A.
Feedback regulationfeedback regulation
- B.
Bioenergetics
- C.
Energy coupling
- D.
Entropy
- E.
Cooperativity
Correct Answer
C. Energy couplingExplanation
Energy coupling is the term used to describe the transfer of free energy from catabolic pathways to anabolic pathways. This process involves the use of energy released from the breakdown of molecules in catabolic pathways to drive the synthesis of molecules in anabolic pathways. Energy coupling is essential for the overall functioning and maintenance of cells, as it allows for the conversion and utilization of energy in different forms to support various cellular processes.Rate this question:
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- 22.
Which of the following statements is true concerning catabolic pathways?
- A.
They combine molecules into more energy-rich molecules.
- B.
They are usually coupled with anabolic pathways to which they supply energy in the form of ATP.
- C.
They are endergonic.
- D.
They are spontaneous and do not need enzyme catalysis.
- E.
They build up complex molecules such as protein from simpler compounds.
Correct Answer
B. They are usually coupled with anabolic pathways to which they supply energy in the form of ATP.Explanation
Catabolic pathways involve the breakdown of larger molecules into smaller ones, releasing energy in the process. This energy is then used to power anabolic pathways, which build up complex molecules from simpler compounds. Therefore, catabolic pathways are usually coupled with anabolic pathways to supply them with energy in the form of ATP.Rate this question:
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- 23.
Which of the following statements regarding ATP is (are) correct?
- A.
ATP serves as a main energy shuttle inside cells.
- B.
ATP drives endergonic reactions in the cell by the enzymatic transfer of the phosphate group to specific reactants.
- C.
The regeneration of ATP from ADP and phosphate is an endergonic reaction.
- D.
A and B only
- E.
A, B, and C
Correct Answer
E. A, B, and CExplanation
ATP serves as a main energy shuttle inside cells, as it carries energy between different cellular processes. ATP drives endergonic reactions in the cell by transferring its phosphate group to specific reactants through enzymatic reactions. Additionally, the regeneration of ATP from ADP and phosphate is an endergonic reaction, meaning it requires energy input. Therefore, statements A, B, and C are all correct.Rate this question:
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- 24.
Which of the following statements is (are) true about enzyme-catalyzed reactions?
- A.
The reaction is faster than the same reaction in the absence of the enzyme.
- B.
The free energy change of the reaction is the same as the reaction in the absence of the enzyme.
- C.
The reaction always goes in the direction toward chemical equilibrium.
- D.
A and B only
- E.
A, B, and C
Correct Answer
A. The reaction is faster than the same reaction in the absence of the enzyme.Explanation
Enzymes are biological catalysts that increase the rate of chemical reactions. They achieve this by lowering the activation energy required for the reaction to occur. As a result, the reaction proceeds faster in the presence of an enzyme compared to the same reaction in the absence of an enzyme. The statement "The reaction is faster than the same reaction in the absence of the enzyme" is therefore true. However, the other statements are not necessarily true. The free energy change of the reaction can be affected by the presence of an enzyme, and the direction of the reaction depends on the specific conditions and equilibrium constants.Rate this question:
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- 25.
How can one increase the rate of a chemical reaction?
- A.
Increase the activation energy needed.
- B.
Cool the reactants.
- C.
Decrease the concentration of the reactants.
- D.
Add a catalyst.
- E.
Increase the entropy of the reactants.
Correct Answer
D. Add a catalyst.Explanation
Adding a catalyst to a chemical reaction can increase the rate of the reaction. A catalyst is a substance that speeds up the reaction by providing an alternative pathway with lower activation energy. It does not get consumed in the reaction and can be used repeatedly. By lowering the activation energy, a catalyst allows more reactant molecules to have sufficient energy to overcome the energy barrier and react. This results in an increased rate of reaction without being consumed in the process.Rate this question:
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- 26.
Sucrose is a disaccharide, composed of the monosaccharides glucose and fructose. The hydrolysis of sucrose by the enzyme sucrase results in
- A.
Bringing glucose and fructose together to form sucrose.
- B.
The release of water from sucrose as the bond between glucose and fructose is broken.
- C.
Breaking the bond between glucose and fructose and forming new bonds from the atoms of water.
- D.
Production of water from the sugar as bonds are broken between the glucose monomers.
- E.
Utilization of water as a covalent bond is formed between glucose and fructose to form sucrase.
Correct Answer
C. Breaking the bond between glucose and fructose and forming new bonds from the atoms of water.Explanation
Sucrose is a disaccharide composed of glucose and fructose. The hydrolysis of sucrose by the enzyme sucrase involves breaking the bond between glucose and fructose. This process requires the addition of water molecules, which are used to form new bonds between the atoms of water and the glucose and fructose molecules, resulting in the formation of separate glucose and fructose molecules. Therefore, the correct answer is breaking the bond between glucose and fructose and forming new bonds from the atoms of water.Rate this question:
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- 27.
Reactants capable of interacting to form products in a chemical reaction must first overcome a thermodynamic barrier known as the reaction's
- A.
Entropy.
- B.
Activation energy.
- C.
Endothermic level.
- D.
Heat content.
- E.
Free-energy content.
Correct Answer
B. Activation energy.Explanation
In a chemical reaction, reactants need to overcome a thermodynamic barrier called activation energy in order to form products. Activation energy is the minimum amount of energy required for a reaction to occur, and it determines the rate at which the reaction proceeds. It is necessary to provide enough energy to break the existing bonds in the reactants and initiate the formation of new bonds in the products. Once the activation energy is surpassed, the reaction can proceed spontaneously. Therefore, activation energy is the correct answer in this case.Rate this question:
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- 28.
A solution of starch at room temperature does not readily decompose to form a solution of simple sugars because
- A.
The starch solution has less free energy than the sugar solution.
- B.
The hydrolysis of starch to sugar is endergonic.
- C.
The activation energy barrier for this reaction cannot be surmounted.
- D.
Starch cannot be hydrolyzed in the presence of so much water.
- E.
Starch hydrolysis is nonspontaneous.
Correct Answer
C. The activation energy barrier for this reaction cannot be surmounted.Explanation
The activation energy barrier refers to the minimum amount of energy required for a chemical reaction to occur. In this case, the hydrolysis of starch to sugar requires breaking the bonds within the starch molecule, which requires a certain amount of energy. At room temperature, the energy available is not sufficient to overcome this activation energy barrier, preventing the decomposition of starch into simple sugars. Therefore, the correct answer is that the activation energy barrier for this reaction cannot be surmounted.Rate this question:
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- 29.
An enzyme catalyzes a reaction by
- A.
Supplying the energy to speed up a reaction.
- B.
Lowering the energy of activation of a reaction.
- C.
Lowering the G of a reaction.
- D.
Changing the equilibrium of a spontaneous reaction.
- E.
Increasing the amount of free energy of a reaction.
Correct Answer
B. Lowering the energy of activation of a reaction.Explanation
Enzymes are biological catalysts that speed up chemical reactions by lowering the energy of activation, which is the energy required to start a reaction. By lowering this energy barrier, enzymes allow reactions to occur more easily and at a faster rate. This is achieved by providing an alternative reaction pathway with a lower activation energy, making it easier for reactant molecules to reach the necessary energy threshold for the reaction to proceed. Therefore, the correct answer is "lowering the energy of activation of a reaction."Rate this question:
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- 30.
During a laboratory experiment, you discover that an enzyme-catalyzed reaction has a G of -20 kcal/mol. If you double the amount of enzyme in the reaction, what will be the G for the new reaction?
- A.
-40 kcal/mol
- B.
-20 kcal/mol
- C.
0 kcal/mol
- D.
+20 kcal/mol
- E.
+40 kcal/mol
Correct Answer
B. -20 kcal/molExplanation
When the amount of enzyme in a reaction is doubled, it does not affect the value of G, which represents the change in Gibbs free energy. The value of G remains the same at -20 kcal/mol.Rate this question:
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- 31.
The active site of an enzyme is the region that
- A.
Binds allosteric regulators of the enzyme.
- B.
Is involved in the catalytic reaction of the enzyme.
- C.
Binds the products of the catalytic reaction.
- D.
Is inhibited by the presence of a coenzyme or a cofactor.
- E.
Both A and B
Correct Answer
B. Is involved in the catalytic reaction of the enzyme.Explanation
The active site of an enzyme is the region that is involved in the catalytic reaction of the enzyme. This means that it is the specific location where the substrate binds and the chemical reaction takes place. The active site typically has a specific shape and chemical properties that allow it to interact with the substrate and facilitate the conversion of the substrate into product. The binding of allosteric regulators, products of the catalytic reaction, and the inhibition by coenzymes or cofactors may occur at other regions of the enzyme, but they are not directly related to the catalytic reaction itself.Rate this question:
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- 32.
According to the induced fit hypothesis of enzyme catalysis, which of the following is CORRECT?
- A.
The binding of the substrate depends on the shape of the active site.
- B.
Some enzymes change their structure when activators bind to the enzyme.
- C.
A competitive inhibitor can outcompete the substrate for the active site.
- D.
The binding of the substrate changes the shape of the enzyme's active site.
- E.
The active site creates a microenvironment ideal for the reaction.
Correct Answer
D. The binding of the substrate changes the shape of the enzyme's active site.Explanation
The induced fit hypothesis of enzyme catalysis suggests that the binding of the substrate causes a conformational change in the enzyme's active site. This change in shape allows for a better fit between the enzyme and the substrate, enhancing the catalytic activity. This explanation aligns with the given correct answer that states "The binding of the substrate changes the shape of the enzyme's active site."Rate this question:
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- 33.
Many different things can alter enzyme activity. Which of the following underlie all types of enzyme regulation?
- A.
Changes in the activation energy of the reaction
- B.
Changes in the active site of the enzyme
- C.
Changes in the free energy of the reaction
- D.
A and B only
- E.
A, B, and C
Correct Answer
D. A and B onlyExplanation
Enzyme activity can be altered by changes in the activation energy of the reaction and changes in the active site of the enzyme. Activation energy refers to the energy required to start a chemical reaction, and any changes in this energy can affect the rate at which the reaction occurs. Similarly, changes in the active site of the enzyme, which is the location where the substrate binds and the reaction takes place, can also impact enzyme activity. Therefore, both A (changes in the activation energy of the reaction) and B (changes in the active site of the enzyme) underlie all types of enzyme regulation.Rate this question:
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- 34.
As temperature decreases, the rate of an enzyme-catalyzed reaction also decreases. Which of the following explain(s) why this occurs?
- A.
Fewer substrates have sufficient energy to get over the activation energy barrier.
- B.
Motion in the active site of the enzyme is slowed, thus slowing the catalysis of the enzyme.
- C.
The motion of the substrate molecules decreases, allowing them to bind more easily to the active site.
- D.
A and B only
- E.
A, B, and C
Correct Answer
D. A and B onlyExplanation
As temperature decreases, the kinetic energy of the molecules decreases, resulting in fewer substrates having sufficient energy to overcome the activation energy barrier. This is explained by option A. Additionally, the motion in the active site of the enzyme is slowed down at lower temperatures, which affects the catalysis of the enzyme. This is explained by option B. Therefore, the correct answer is A and B only.Rate this question:
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- 35.
What is a nonprotein "helper" of an enzyme molecule called?
- A.
Accessory enzyme
- B.
Allosteric group
- C.
Coenzyme
- D.
Functional group
- E.
Enzyme activator
Correct Answer
C. CoenzymeExplanation
A nonprotein "helper" of an enzyme molecule is called a coenzyme. Coenzymes are small organic molecules that bind to the enzyme and assist in the catalytic process. They are essential for the proper functioning of many enzymes as they provide necessary chemical groups or transfer chemical groups between enzymes. Coenzymes often act as carriers of specific atoms or functional groups during enzymatic reactions. They can be derived from vitamins or synthesized within the body.Rate this question:
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- 36.
Which of the following is true of enzymes?
- A.
Enzymes may require a nonprotein cofactor or ion for catalysis to take place.
- B.
Enzyme function is reduced if the three-dimensional structure or conformation of an enzyme is altered.
- C.
Enzyme function is influenced by physical and chemical environmental factors such as pH and temperature.
- D.
Enzymes increase the rate of chemical reaction by lowering activation energy barriers.
- E.
All of the above are true of enzymes.
Correct Answer
E. All of the above are true of enzymes.Explanation
Enzymes may require a nonprotein cofactor or ion for catalysis to take place. Enzyme function is reduced if the three-dimensional structure or conformation of an enzyme is altered. Enzyme function is influenced by physical and chemical environmental factors such as pH and temperature. Enzymes increase the rate of chemical reaction by lowering activation energy barriers. Therefore, all of the above statements are true of enzymes.Rate this question:
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- 37.
The mechanism in which the end product of a metabolic pathway inhibits an earlier step in the pathway is known as
- A.
Metabolic inhibition.metabolic inhibition.
- B.
Feedback inhibition.
- C.
Allosteric inhibition.
- D.
Noncooperative inhibition.
- E.
Reversible inhibition.
Correct Answer
B. Feedback inhibition.Explanation
Feedback inhibition is the mechanism in which the end product of a metabolic pathway inhibits an earlier step in the pathway. This allows the cell to regulate the production of certain molecules by slowing down or stopping the pathway when enough of the end product has been produced. This helps maintain homeostasis and prevent the accumulation of excess molecules. Feedback inhibition is a common regulatory mechanism in many metabolic pathways and is essential for proper cellular function.Rate this question:
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- 38.
The free energy for the oxidation of glucose to CO2 and water is -686 kcal/mole and the free energy for the reduction of NAD+ to NADH is +53 kcal/mole. Why are only two molecules of NADH formed during glycolysis when it appears that as many as a dozen could be formed?
- A.
Most of the free energy available from the oxidation of glucose is used in the production of ATP in glycolysis.
- B.
Glycolysis is a very inefficient reaction, with much of the energy of glucose released as heat.
- C.
Most of the free energy available from the oxidation of glucose remains in pyruvate, one of the products of glycolysis.
- D.
There is no CO2 or water produced as products of glycolysis.
- E.
Glycolysis consists of many enzymatic reactions, each of which extracts some energy from the glucose molecule.
Correct Answer
C. Most of the free energy available from the oxidation of glucose remains in pyruvate, one of the products of glycolysis.Explanation
During glycolysis, glucose is oxidized to pyruvate. However, only a small amount of the free energy available from the oxidation of glucose is captured in the form of ATP and NADH. Most of the free energy is actually stored in the pyruvate molecules that are produced. This is why only two molecules of NADH are formed during glycolysis, despite the potential for more. The majority of the free energy is still present in the pyruvate, which can then be further metabolized in other pathways to extract more energy.Rate this question:
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- 39.
A molecule that is phosphorylated
- A.
Has an increased chemical reactivity; it is primed to do cellular work.
- B.
Has a decreased chemical reactivity; it is less likely to provide energy for cellular work.
- C.
Has been oxidized as a result of a redox reaction involving the gain of an inorganic phosphate.
- D.
Has been reduced as a result of a redox reaction involving the loss of an inorganic phosphate.
- E.
Has less energy than before its phosphorylation and therefore less energy for cellular work.
Correct Answer
A. Has an increased chemical reactivity; it is primed to do cellular work.Explanation
When a molecule is phosphorylated, it means that a phosphate group has been added to it. This addition of a phosphate group increases the chemical reactivity of the molecule. The phosphate group contains high-energy bonds that can be easily broken, releasing energy that can be used for cellular work. Therefore, a phosphorylated molecule is primed and ready to participate in various cellular processes and provide energy for cellular work.Rate this question:
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- 40.
During cellular respiration, acetyl CoA accumulates in which location?
- A.
Cytosol
- B.
Mitochondrial outer membrane
- C.
Mitochondrial inner membrane
- D.
Mitochondrial intermembrane space
- E.
Mitochondrial matrix
Correct Answer
E. Mitochondrial matrixExplanation
During cellular respiration, acetyl CoA is produced in the cytosol and then transported into the mitochondria. Once inside the mitochondria, acetyl CoA enters the citric acid cycle, also known as the Krebs cycle, which takes place in the mitochondrial matrix. Therefore, the correct answer is mitochondrial matrix.Rate this question:
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- 41.
How many carbon atoms are fed into the citric acid cycle as a result of the oxidation of one molecule of pyruvate?
- A.
2
- B.
4
- C.
6
- D.
8
- E.
10
Correct Answer
A. 2Explanation
In the citric acid cycle, one molecule of pyruvate is oxidized to produce one molecule of acetyl-CoA. Acetyl-CoA has two carbon atoms. Therefore, as a result of the oxidation of one molecule of pyruvate, two carbon atoms are fed into the citric acid cycle.Rate this question:
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- 42.
Starting with one molecule of isocitrate and ending with fumarate, what is the maximum number of ATP molecules that could be made through substrate-level phosphorylation?
- A.
1
- B.
2
- C.
11
- D.
12
- E.
24
Correct Answer
A. 1Explanation
Substrate-level phosphorylation is a process in which ATP is directly synthesized from a phosphorylated substrate molecule. In the citric acid cycle, isocitrate is converted to alpha-ketoglutarate, producing one molecule of ATP through substrate-level phosphorylation. Therefore, the maximum number of ATP molecules that could be made through substrate-level phosphorylation in this pathway is 1.Rate this question:
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- 43.
Carbon skeletons for amino acid biosynthesis are supplied by intermediates of the citric acid cycle. Which intermediate would supply the carbon skeleton for synthesis of a five-carbon amino acid?
- A.
Succinate
- B.
Malate
- C.
Citrate
- D.
Alpha-ketoglutarate
- E.
Isocitrate
Correct Answer
D. Alpha-ketoglutarateExplanation
Alpha-ketoglutarate is an intermediate of the citric acid cycle that can supply the carbon skeleton for the synthesis of a five-carbon amino acid. The citric acid cycle is a central metabolic pathway that produces energy and precursor molecules for various cellular processes. Alpha-ketoglutarate is a key intermediate in this cycle and can be converted into glutamate, which is a precursor for several amino acids, including those with a five-carbon backbone. Therefore, alpha-ketoglutarate is the most likely intermediate to supply the carbon skeleton for the synthesis of a five-carbon amino acid.Rate this question:
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- 44.
Starting with one molecule of citrate and ending with oxaloacetate, how many ATP molecules can be formed from oxidative phosphorylation (chemiosmosis)?
- A.
1
- B.
3
- C.
4
- D.
11
- E.
12
Correct Answer
D. 11Explanation
In oxidative phosphorylation (chemiosmosis), ATP molecules are produced through the electron transport chain. Each NADH molecule can produce 3 ATP molecules, while each FADH2 molecule can produce 2 ATP molecules. Since citrate is metabolized to produce 3 NADH molecules and 1 FADH2 molecule, the total ATP molecules that can be formed from oxidative phosphorylation is 3 * 3 + 1 * 2 = 11.Rate this question:
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- 45.
How many reduced dinucleotides would be produced with four turns of the citric acid cycle?
- A.
1 FADH2 and 4 NADH
- B.
2 FADH2 and 8 NADH
- C.
4 FADH2 and 12 NADH
- D.
1 FAD and 4 NAD+
- E.
4 FAD+ and 12 NAD+
Correct Answer
C. 4 FADH2 and 12 NADHExplanation
In the citric acid cycle, each turn produces 1 FADH2 and 3 NADH. Since there are four turns of the cycle, the total number of reduced dinucleotides produced would be 4 FADH2 and 12 NADH.Rate this question:
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- 46.
Starting with citrate, how many of the following would be produced with three turns of the citric acid cycle?
- A.
1 ATP, 2 CO2, 3 NADH, and 1 FADH2
- B.
2 ATP, 2 CO2, 1 NADH, and 3 FADH2
- C.
3 ATP, 3 CO2, 3 NADH, and 3 FADH2
- D.
3 ATP, 6 CO2, 9 NADH, and 3 FADH2
- E.
38 ATP, 6 CO2, 3 NADH, and 12 FADH2
Correct Answer
D. 3 ATP, 6 CO2, 9 NADH, and 3 FADH2Explanation
In each turn of the citric acid cycle, one ATP is produced through substrate-level phosphorylation. Two CO2 molecules are released as byproducts. Three NADH molecules are produced through redox reactions, and one FADH2 molecule is also produced. Since the question asks for the products after three turns of the cycle, we multiply each of the quantities by three. Therefore, the correct answer is 3 ATP, 6 CO2, 9 NADH, and 3 FADH2.Rate this question:
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- 47.
Carbon dioxide (CO2) is released during which of the following stages of cellular respiration?
- A.
Glycolysis and the oxidation of pyruvate to acetyl CoA
- B.
Oxidation of pyruvate to acetyl CoA and the citric acid cycle
- C.
The citric acid cycle and oxidative phosphorylation
- D.
Oxidative phosphorylation and fermentation
- E.
Fermentation and glycolysis
Correct Answer
B. Oxidation of pyruvate to acetyl CoA and the citric acid cycle -
- 48.
Where do the catabolic products of fatty acid breakdown enter into the citric acid cycle?
- A.
Pyruvate
- B.
Malate or fumarate
- C.
Acetyl CoA
- D.
Alpha-ketoglutarate
- E.
Succinyl CoA
Correct Answer
C. Acetyl CoAExplanation
The catabolic products of fatty acid breakdown enter into the citric acid cycle through acetyl CoA. Acetyl CoA is derived from the breakdown of fatty acids and serves as the entry point for fatty acid metabolism in the citric acid cycle. It combines with oxaloacetate to form citrate, initiating the cycle and allowing for the production of energy through the oxidation of acetyl CoA.Rate this question:
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- 49.
Where are the proteins of the electron transport chain located?
- A.
Cytosol
- B.
Mitochondrial outer membrane
- C.
Mitochondrial inner membrane
- D.
Mitochondrial intermembrane space
- E.
Mitochondrial matrix
Correct Answer
C. Mitochondrial inner membraneExplanation
The proteins of the electron transport chain are located in the mitochondrial inner membrane. This is where the electron transport chain takes place, a series of protein complexes that transfer electrons from electron donors to electron acceptors, generating energy in the form of ATP. The inner membrane of the mitochondria is highly folded, forming structures called cristae, which provide a large surface area for the electron transport chain proteins to carry out their function efficiently.Rate this question:
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- 50.
Which of the following describes the sequence of electron carriers in the electron transport chain, starting with the least electronegative?
- A.
Ubiquinone (Q), cytochromes (Cyt), FMN, Fe•S
- B.
Cytochromes (Cyt), FMN, ubiquinone, Fe·S
- C.
Fe•S, FMN, cytochromes (Cyt), ubiquinone
- D.
FMN, Fe•S, ubiquinone, cytochromes (Cyt)
- E.
Cytochromes (Cyt), Fe•S, ubiquinone, FMN
Correct Answer
D. FMN, Fe•S, ubiquinone, cytochromes (Cyt)Explanation
The correct answer is FMN, Fe•S, ubiquinone, cytochromes (Cyt). This sequence describes the order of electron carriers in the electron transport chain, starting with the least electronegative. FMN (flavin mononucleotide) is the first carrier, followed by Fe•S (iron-sulfur clusters), then ubiquinone, and finally cytochromes (Cyt). This sequence reflects the transfer of electrons from carriers with lower electronegativity to carriers with higher electronegativity, allowing for the generation of ATP through oxidative phosphorylation.Rate this question:
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Mar 21, 2023Quiz Edited by
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