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Chapter 8 - Energy and Enzymes: An Introduction to Metabolic Pathways
Biological Science, 5e (Freeman)
Terms in this set (45)
Which of the following is a statement of the first law of thermodynamics?
A) Energy cannot be created or destroyed.
For living organisms, which of the following is an important consequence of the first law of thermodynamics?
B) The organism ultimately must obtain all of the necessary energy for life from its environment.
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?
D) As a consequence of growing, organisms cause a greater increase in entropy in their environment than the decrease in entropy associated with their growth.
Whenever energy is transformed, there is always an increase in the _____.
D) entropy of the universe
Which of the following statements is a logical consequence of the second law of thermodynamics?
D) Every chemical reaction must increase the total entropy of the universe.
Which of the following statements is representative of the second law of thermodynamics?
D) Cells require a constant input of energy to maintain their high level of organization.
Which of the following is an example of potential rather than kinetic energy?
D) a molecule of glucose
The mathematical expression for the change in free energy of a system is ΔG =ΔH - TΔS. Which of the following is (are) correct?
C) ΔG is the change in free energy.
A system at chemical equilibrium _____.
E) can do no work
A chemical reaction that has a positive ΔG is best described as _____.
Enthalpy (H) is the _____.
B) total energy in biological systems
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
Which of the following is true for all exergonic reactions?
B) The reaction proceeds with a net release of free energy.
Why is ATP an important molecule in metabolism?
B) It provides energy coupling between exergonic and endergonic reactions.
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?
E) Reactant and product concentrations in the test tube are different from those in the cell.
Catabolic pathways _____.
B) supply energy, primarily in the form of ATP, for the cell's work
When chemical, transport, or mechanical work is done by an organism, what happens to the heat generated?
D) It is lost to the environment.
Which of the following is true when comparing an uncatalyzed reaction to the same reaction with a catalyst?
B) The catalyzed reaction will have the same ∆G.
You have discovered an enzyme that can catalyze two different chemical reactions. Which of the following is most likely to be correct?
D) Either the enzyme has two distinct active sites or the reactants involved in the two reactions are very similar in size and shape.
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 _____.
The lock-and-key analogy for enzymes applies to the specificity of enzymes _____.
C) binding to their substrate
Which of the following statements is true about enzyme-catalyzed reactions?
A) The reaction is faster than the same reaction in the absence of the enzyme.
Reactants capable of interacting to form products in a chemical reaction must first overcome a thermodynamic barrier known as the reaction's _____.
B) activation energy
A solution of starch at room temperature does not readily decompose to form a solution of simple sugars because _____.
C) the activation energy barrier for this reaction cannot easily be surmounted at room temperature
B) increase the rate of a reaction by lowering the activation energy barrier
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?
B) -20 kcal/mol
The active site of an enzyme is the region that _____.
B) is involved in the catalytic reaction of the enzyme
According to the induced fit hypothesis of enzyme catalysis, _____.
D) the binding of the substrate changes the shape of the enzyme's active site
Which of the following is true of enzymes?
D) Enzymes increase the rate of chemical reaction by providing activation energy to the substrate.
Zinc, an essential trace element for most organisms, is present in the active site of the enzyme carboxypeptidase. The zinc most likely functions as _____.
D) a cofactor necessary for enzyme activity
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?
B) The binding of the first two molecules must cause a 3-D change that opens another active site on the enzyme.
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 them resistant to these competitive inhibitors. Where in the reverse transcriptase enzyme would such amino acid changes most likely occur in drug-resistant viruses?
A) in or near the active site
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 bonding 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?
B) It is probably an enzyme that works through allosteric regulation.
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?
D) competitive inhibition
Mutations that result in a single amino acid substitution in an enzyme _____.
D) may change the enzyme's optimal temperature or optimal pH
Increasing the substrate concentration in an enzymatic reaction could overcome which of the following?
C) competitive inhibition
A noncompetitive inhibitor decreases the rate of an enzyme reaction by _____.
B) changing the shape of the enzyme's active site
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?
C) water solubility
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?
C) by changing the shape of an enzyme
Some bacteria are metabolically active in hot springs because _____.
C) their enzymes have high optimal temperatures
Which term most precisely describes the cellular process of breaking down large molecules into smaller ones?
A) catabolism (catabolic pathways)
Anabolic pathways _____.
C) consume energy to build up polymers from monomers
When ATP releases some energy, it also releases inorganic phosphate. What happens to the inorganic phosphate in the cell?
D) It may be used to form a phosphorylated intermediate.
The mechanism in which the end product of a metabolic pathway inhibits an earlier step in the pathway is most precisely described as _____.
B) feedback inhibition
Choose the pair of terms that correctly completes this sentence: Catabolism is to anabolism as _____ is to _____.
B) exergonic; endergonic
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