Deck 8: Energy and Enzymes

Question 1

For living organisms, which of the following is an important consequence of the first law of thermodynamics?

A) Organisms grow by converting energy into organic matter.
B) Life does not obey the first law of thermodynamics.
C) The energy content of an organism is constant.
D) The organism ultimately must obtain all of the necessary energy for life from its environment.
E) The entropy of an organism decreases with time as the organism grows in complexity.

Answer 1

D

Question 2

Living organisms increase in complexity as they grow, resulting in a decrease in the entropy of an organism. How does this relate to the second law of thermodynamics?

A) Living organisms do not obey the second law of thermodynamics, which states that entropy must increase with time.
B) Living organisms are able to transform energy into entropy.
C) As a consequence of growing, organisms cause a greater increase in entropy in their environment than the decrease in entropy associated with their growth.
D) Living organisms do not follow the laws of thermodynamics.
E) Living organisms are able to transform entropy into energy.

Answer 2

C

Question 3

Which of the following is true for all exergonic reactions?

A) The reaction goes only in a forward direction: All reactants will be converted to products, but no products will be converted to reactants.
B) A net input of energy from the surroundings is required for the reactions to proceed.
C) The reactions are rapid.
D) The reaction proceeds with a net release of free energy.
E) The products have more total energy than the reactants.

Answer 3

D

Question 4

Which of the following is a statement of the first law of thermodynamics?

A) Kinetic energy is stored energy that results from the specific arrangement of matter.
B) The entropy of the universe is constant.
C) The entropy of the universe is decreasing.
D) Energy cannot be transferred or transformed.
E) Energy cannot be created or destroyed.

Question 5

Whenever energy is transformed, there is always an increase in the

A) entropy of the universe.
B) free energy of the universe.
C) free energy of the system.
D) enthalpy of the universe.
E) entropy of the system.

Question 6

Which of the following statements is representative of the second law of thermodynamics?

A) Heat represents a form of energy that can be used by most organisms to do work.
B) Without an input of energy, organisms would tend toward decreasing entropy.
C) Every energy transformation by a cell decreases the entropy of the universe.
D) Cells require a constant input of energy to maintain their high level of organization.
E) Conversion of energy from one form to another is always accompanied by some gain of free energy.

Question 7

A chemical reaction that has a positive OG is best described as

A) entropic.
B) endergonic.
C) enthalpic.
D) exergonic.
E) spontaneous.

Question 8

Use the figure below to answer the following questions).

How do cells use the ATP cycle shown in the figure above?

A) Cells use the cycle to recycle the energy released by ATP hydrolysis.
B) Cells use the cycle to generate or consume water molecules as needed.
C) Cells use the cycle to recycle ADP, phosphate, and the energy released by ATP hydrolysis.
D) Cells use the cycle primarily to generate heat.
E) Cells use the cycle to recycle ADP and phosphate.

Question 9

Which of the following is true when comparing an uncatalyzed reaction to the same reaction with a catalyst?

A) The catalyzed reaction will consume all of the catalyst.
B) The catalyzed reaction will be slower.
C) The catalyzed reaction will only be limited by the amount of substrate.
D) The catalyzed reaction will have the same AG.
E) The catalyzed reaction will have higher activation energy.

Question 10

Biological evolution of life on Earth, from simple prokaryote- like cells to large, multicellular eukaryotic organisms,

A) has occurred in accordance with the laws of thermodynamics.
B) has occurred in accordance with the laws of thermodynamics, by expending Earth's energy resources and causing an increase in the entropy of the planet.
C) has been made possible by expending Earth's energy resources.
D) has caused an increase in the entropy of the planet.
E) violates the laws of thermodynamics because Earth is a closed system.

Question 11

Which of the following statements is a logical consequence of the second law of thermodynamics?

A) Energy can be transferred or transformed, but it cannot be created or destroyed.
B) If the entropy of a system increases, there must be a corresponding decrease in the entropy of the universe.
C) Every energy transfer requires activation energy from the environment.
D) If there is an increase in the energy of a system, there must be a corresponding decrease in the energy of the rest of the universe.
E) Every chemical reaction must increase the total entropy of the universe.

Question 12

Use the figure below to answer the following questions).


-Which of the following is the most correct interpretation of the figure provided?

A) Energy from catabolism can be used directly for performing cellular work.
B) ^{ADP +} Pi ^{are a set of molecules that store energy for catabolism.}
C) Pi ^{acts as a shuttle molecule to move energy from ATP to ADP.}
D) ATP is a molecule that acts as an intermediary to store energy for cellular work.
E) Inorganic phosphate is created from organic phosphate.

Question 13

Enthalpy H) is the

A) system's entropy.
B) total kinetic energy of a system.
C) cell's energy equilibrium.
D) condition of a cell that is not able to react.
E) total energy in biological systems.

Question 14

A system at chemical equilibrium

A) has zero kinetic energy.
B) consumes or releases energy, depending on whether it is exergonic or endergonic.
C) releases energy at a steady rate.
D) can do no work.
E) consumes energy at a steady rate.

Question 15

Why is ATP an important molecule in metabolism?

A) It is one of the four building blocks for DNA synthesis.
B) Its terminal phosphate group contains a strong covalent bond that, when hydrolyzed, releases free energy.
C) Its hydrolysis provides an input of free energy for exergonic reactions.
D) It provides energy coupling between exergonic and endergonic reactions.
E) Its terminal phosphate bond has higher energy than the other two phosphate bonds.

Question 16

Which of the following is an example of potential rather than kinetic energy?

A) a molecule of glucose
B) the muscle contractions of a person mowing grass
C) water rushing over Niagara Falls
D) light flashes emitted by a firefly
E) a crawling beetle foraging for food

Question 17

The mathematical expression for the change in free energy of a system is OG =OH - TOS. Which of the following is are) correct?

A) OS is the change in enthalpy, a measure of randomness.
B) T is the temperature in degrees Celsius.
C) OH is the change in entropy, the energy available to do work.
D) OG is the change in free energy.

Question 18

Catabolic pathways

A) combine molecules into more energy- rich molecules.
B) supply energy, primarily in the form of ATP, for the cell's work.
C) build up complex molecules such as protein from simpler compounds.
D) are spontaneous and do not need enzyme catalysis.
E) are endergonic.

Question 19

When 10 000 molecules of ATP are hydrolyzed to ADP and _i in a test tube, about half 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) The hydrolysis of ATP in a cell produces different chemical products than does the reaction in a test tube.
B) Reactant and product concentrations in the test tube are different from those in the cell.
C) The reaction in cells must be catalyzed by enzymes, but the reaction in a test tube does not need enzymes.
D) Cells are less efficient at heat production than nonliving systems.
E) Cells are open systems, but a test tube is an isolated system.

Question 20

When chemical, transport, or mechanical work is done by an organism, what happens to the heat generated?

A) It is used to power yet more cellular work.
B) It is transported to specific organs such as the brain.
C) It is used to store energy as more ATP.
D) It is lost to the environment.
E) It is used to generate ADP from nucleotide precursors.

Question 21

The active site of an enzyme is the region that

A) aids in increasing the activation energy of the reaction.
B) is inhibited by the presence of a coenzyme or a cofactor.
C) is involved in the catalytic reaction of the enzyme.
D) binds noncompetitive inhibitors of the enzyme.
E) binds allosteric regulators of the enzyme.

Question 22

According to the induced fit hypothesis of enzyme catalysis,

A) the active site creates a microenvironment ideal for the reaction.
B) the binding of the substrate depends on the shape of the active site.
C) the binding of the substrate changes the shape of the enzyme's active site.
D) some enzymes change their structure when activators bind to the enzyme.
E) a competitive inhibitor can outcompete the substrate for the active site.

Question 23

Which of the following represents the difference between the free- energy content of the reactants and the free- energy content of the products in the figure?

A) a
B) b
C) c
D) d
E) e

Question 24

To attach a particular amino acid to the tRNA molecule that will transport it, an enzyme, an aminoacyl- tRNA synthetase, is required, along with ATP. Initially, the enzyme has an active site for ATP and another for the amino acid, but it is not able to attach the tRNA. What must occur for the final attachment to occur?

A) The ATP must be hydrolyzed to allow the amino acid to bind to the synthetase.
B) The tRNA molecule must alter its shape to be able to fit into the active site with the other two molecules.
C) The binding of the first two molecules must cause a 3- D change that opens another active site on the enzyme.
D) The ATP must first have to attach to the tRNA.
E) The 3' end of the tRNA must be cleaved before it can have an attached amino acid.

Question 25

Which of the following represents the OG of the reaction in the figure?

A) a
B) b
C) c
D) d
E) e

Question 26

A solution of starch at room temperature does not readily decompose to form a solution of simple sugars because

A) starch cannot be hydrolyzed in the presence of so much water.
B) starch hydrolysis is nonspontaneous.
C) the starch solution has less free energy than the sugar solution.
D) the activation energy barrier for this reaction cannot easily be surmounted at room temperature.
E) the hydrolysis of starch to sugar is endergonic.

Question 27

Enzymes

A) change the equilibrium point of the reactions they catalyze.
B) increase the rate of a reaction by lowering the activation energy barrier.
C) make the rate of a reaction independent of substrate concentrations.
D) increase the rate of a reaction by reducing the rate of reverse reactions.
E) increase the rate of a reaction by making the reaction more exergonic.

Question 28

Which of the following is true of enzymes?

A) Enzymes increase the rate of chemical reaction by providing activation energy to the substrate.
B) Enzyme function is increased if the three- dimensional structure or conformation of an enzyme is altered.
C) Enzymes increase the rate of chemical reaction by increasing AG.
D) Enzyme function is independent of physical and chemical environmental factors such as pH and temperature.
E) Enzymes increase the rate of chemical reaction by the lowering activation energy required.

Question 29

Which of the following in the figure would be the same in either an enzyme- catalyzed or a noncatalyzed reaction?

A) a
B) b
C) c
D) d
E) e

Question 30

During a laboratory experiment, you discover that an enzyme- catalyzed reaction has a AG of - 20 kcal/mol. If you double the amount of enzyme in the reaction, what will be the AG for the new reaction?

A) 0 kcal/mol
B) +40 kcal/mol
C) - 20 kcal/mol
D) +20 kcal/mol
E) - 40 kcal/mol

Question 31

Reactants capable of interacting to form products in a chemical reaction must first overcome a thermodynamic barrier known as the reaction's

A) activation energy.
B) equilibrium point.
C) entropy.
D) endothermic level.
E) free- energy content.

Question 32

The following questions) are based on the reaction A + B -C + D shown in the figure provided.

Which of the following terms best describes the forward reaction in the figure?

A) endergonic, AG > 0
B) endergonic, AG < 0
C) exergonic, AG < 0
D) chemical equilibrium, AG = 0
E) exergonic, AG > 0

Question 33

The lock- and- key analogy for enzymes applies to the specificity of enzymes

A) interacting with ions.
B) as they form their tertiary structure.
C) interacting with water.
D) as they form their tertiary and quaternary structure.
E) binding to their substrate.

Question 34

Which of the following statements is true about enzyme- catalyzed reactions?

A) Enzyme- catalyzed reactions release more free energy than noncatalyzed reactions.
B) An enzyme catalyzes a reaction by raising the activation energy.
C) The reaction is faster than the same reaction in the absence of the enzyme.
D) Enzyme- catalyzed reactions require energy to activate the enzyme.
E) The free- energy change of the reaction is opposite from the reaction that occurs in the absence of the enzyme.

Question 35

Some of the drugs used to treat HIV patients are competitive inhibitors of the HIV reverse transcriptase enzyme. Unfortunately, the high mutation rate of HIV means that the virus rapidly acquires mutations with amino acid changes that make reverse transcriptase resistant to these competitive inhibitors. Where in the reverse transcriptase enzyme would such amino acid changes most likely occur in drug- resistant viruses?

A) at an allosteric site
B) in regions of the protein that determine packaging into the virus capsid
C) at a cofactor binding site
D) in or near the active site
E) Such mutations could occur anywhere with equal probability.

Question 36

Consider the HIV enzyme called protease. The amino acid residues at the active site are highly hydrophobic. In designing a drug that would bind to the active site and jam it, researchers should use a molecule that is

A) hydrophobic.
B) basic.
C) charged.
D) polar.
E) acidic.

Question 37

Zinc, an essential trace element for most organisms, is present in the active site of the enzyme carboxypeptidase. The zinc most likely functions as

A) a noncompetitive inhibitor of the enzyme.
B) a cofactor necessary for enzyme activity.
C) a competitive inhibitor of the enzyme.
D) a coenzyme derived from a vitamin.
E) an allosteric activator of the enzyme.

Question 38

Rate of an enzyme- catalyzed reaction as a function of varying reactant concentration, with the concentration of enzyme constant.
In the graph provided, why does the reaction rate plateau at higher reactant concentrations?

A) The rate of the reverse reaction increases with reactant concentration.
B) The reaction nears equilibrium at high reactant concentrations.
C) Feedback inhibition by product occurs at high reactant concentrations.
D) The activation energy for the reaction increases with reactant concentration.
E) Most enzyme molecules are occupied by substrate at high reactant concentrations.

Question 39

Which of the following represents the activation energy needed for the enzyme- catalyzed reverse reaction, C +
D -A + B, in the figure?

A) a
B) b
C) c
D) d
E) e

Question 40

You have discovered an enzyme that can catalyze two different chemical reactions. Which of the following is most likely to be correct?

A) Two types of allosteric regulation occur: the binding of one molecule activates the enzyme while the binding of a different molecule inhibits it.
B) The enzyme must be flexible and composed of two different subunits.
C) Either the enzyme has two distinct active sites or the reactants involved in the two reactions are very similar in size and shape.
D) The enzyme contains a- helices and fi- pleated sheets.
E) The enzyme is subject to competitive inhibition and allosteric regulation.

Question 41

Mutations that result in a single amino acid substitution in an enzyme

A) cannot affect the activity or properties of the enzyme.
B) will destroy the activity of the enzyme.
C) may, in rare cases, cause the enzyme to run reactions in reverse.
D) will change the substrate specificity of the enzyme.
E) may change the enzyme's optimal temperature or optimal pH.

Question 42

Use the following information to answer the corresponding questions).
A series of enzymes catalyze the reaction X -Y -Z -A. Product A binds to the enzyme that converts X to Y at a position remote from its active site. This binding decreases the activity of the enzyme.
What is substance X?

A) the product
B) a substrate
C) a coenzyme
D) an intermediate
E) an allosteric inhibitor

Question 43

Activity of various enzymes at various temperatures a) and at various pH b). Use the image above to answer the following
questions).
Which curves on the graphs provided may represent the temperature and pH profiles of an enzyme taken from a bacterium that lives in a mildly alkaline hot springs at temperatures of 70°C or higher?

A) curves 2 and 4
B) curves 1 and 5
C) curves 3 and 4
D) curves 2 and 5
E) curves 3 and 5

Question 44

Activity of various enzymes at various temperatures a) and at various pH b). Use the image above to answer the following
questions).
Which temperature and pH profile curves on the graphs were most likely generated from analysis of an enzyme from a human stomach where conditions are strongly acid?

A) curves 1 and 5
B) curves 1 and 4
C) curves 3 and 4
D) curves 2 and 4
E) curves 2 and 5

Question 45

Increasing the substrate concentration in an enzymatic reaction could overcome which of the following?

A) competitive inhibition
B) high activation energy
C) the need for a coenzyme
D) insufficient cofactors
E) allosteric inhibition

Question 46

How might a change of one amino acid at a site, distant from the active site of an enzyme, alter an enzyme's substrate specificity?

A) by changing the enzyme's pH optimum
B) by changing the enzyme's binding of allosteric regulator
C) by changing the enzyme's location in the cell
D) by changing the shape of an enzyme
E) An amino acid change away from the active site cannot alter the enzyme's substrate specificity.

Question 47

An important group of peripheral membrane proteins are enzymes such as the phospholipases that cleave the head groups of phospholipids. What properties must these enzymes exhibit?

A) lipid solubility
B) resistance to degradation
C) water solubility
D) independence from cofactor interaction
E) membrane- spanning domains

Question 48

Which of the following represents the activation energy needed for the noncatalyzed reverse reaction, C + D -A
+ B, in the figure?

A) a
B) b
C) c
D) d
E) e

Question 49

HIV is the virus that causes AIDS. In the mid- 1990s, researchers discovered an enzyme in HIV called protease. Once the enzyme's structure was known, researchers began looking for drugs that would fit into the active site and block it. If this strategy for stopping HIV infections were successful, it would be an example of what phenomenon?

A) allosteric regulation
B) denaturation
C) vaccination
D) feedback inhibition
E) competitive inhibition

Question 50

You have isolated a previously unstudied protein, identified its complete structure in detail, and determined that it catalyzes the breakdown of a large substrate. You notice it has two binding sites. One of these is large, apparently the binding site for the large substrate; the other is small, possibly a binding site for a regulatory molecule. What do these findings tell you about the mechanism of this protein?

A) It is probably an enzyme that works through allosteric regulation.
B) It is probably a structural protein found in cartilage or skeletal tissue.
C) It is probably an enzyme that works through competitive inhibition.
D) It is probably a cell membrane transport protein-like an ion channel.
E) It is probably a structural protein that is involved in cell- to- cell adhesion.

Question 51

Choose the pair of terms that correctly completes this sentence: Catabolism is to anabolism as _ is to
)

A) exergonic; spontaneous
B) free energy; entropy
C) exergonic; endergonic
D) entropy; enthalpy
E) work; energy

Question 52

Which of the following represents the activation energy required for a noncatalyzed reaction in the figure?

A) a
B) b
C) c
D) d
E) e

Question 53

An allosteric regulator decreases the rate of an enzyme reaction by

A) changing the shape of the enzyme's active site.
B) changing the overall free energy of the reaction.
C) acting as a coenzyme for the reaction.
D) binding at the active site of the enzyme.
E) decreasing the activation energy of the reaction.

Question 54

Which term most precisely describes the cellular process of breaking down large molecules into smaller ones?

A) catabolism catabolic pathways)
B) metabolism
C) anabolism anabolic pathways)
D) denaturation
E) dehydration

Question 55

Use the following information to answer the corresponding questions).
A series of enzymes catalyze the reaction X -Y -Z -A. Product A binds to the enzyme that converts X to Y at a position remote from its active site. This binding decreases the activity of the enzyme.
With respect to the enzyme that converts X to Y, substance A functions as

A) a competitive inhibitor.
B) an allosteric inhibitor.
C) an intermediate.
D) the substrate.
E) a coenzyme.

Question 56

Anabolic pathways

A) consume energy to decrease the entropy of the organism and its environment.
B) consume energy to build up polymers from monomers.
C) do not depend on enzymes.
D) are usually highly spontaneous chemical reactions.
E) release energy as they degrade polymers to monomers.

Question 57

When ATP releases some energy, it also releases inorganic phosphate. What happens to the inorganic phosphate in the cell?

A) It is added to water and excreted as a liquid.
B) It enters the nucleus and affects gene expression.
C) It is used only to regenerate more ATP.
D) It may be used to form a phosphorylated intermediate.
E) It is secreted as waste.

Question 58

Some bacteria are metabolically active in hot springs because

A) high temperatures make catalysis unnecessary.
B) their enzymes have high optimal temperatures.
C) their enzymes are completely insensitive to temperature.
D) they are able to maintain a lower internal temperature.
E) they use molecules other than proteins or RNAs as their main catalysts.

Question 59

The mechanism in which the end product of a metabolic pathway inhibits an earlier step in the pathway is most precisely described as inhibition.

A) feedback
B) reversible
C) allosteric
D) noncooperative
E) metabolic