Biology Ch. 6 Assessment
3) Which of the following is a statement of the first law of thermodynamics?
A) Energy cannot be created or destroyed.
27) 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.
67) If an enzyme in solution is saturated with substrate, the most effective way to obtain a faster yield of products is to
A) add more of the enzyme.
9) Which of the following types of reactions would decrease the entropy within a cell?
A) anabolic reactions
16) A chemical reaction that has a positive ΔG is best described as
A) endergonic.
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.
39) 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
31) 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
66) Which of the following metabolic processes can occur without a net influx of energy from some other process?
B) C6H12O6 + 6 O2 → 6 CO2 + 6 H2O
19) Why is ATP an important molecule in metabolism?
B) It provides energy coupling between exergonic and endergonic reactions.
38) In order 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 in order 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.
4) 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.
15) Which of the following is true for all exergonic reactions?
B) The reaction proceeds with a net release of free energy.
40) Protein kinases are enzymes that transfer the terminal phosphate from ATP to an amino acid residue on the target protein. Many are located on the plasma membrane as integral membrane proteins or peripheral membrane proteins. What purpose may be served by their plasma membrane localization?
B) They can more readily encounter and phosphorylate other membrane proteins.
22) Which of the following statements is true concerning catabolic pathways?
B) They supply energy, primarily in the form of ATP, for the cell's work.
28) 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.
42) How does a noncompetitive inhibitor decrease the rate of an enzyme reaction?
B) by changing the shape of the enzyme's active site
64) Choose the pair of terms that correctly completes this sentence: Catabolism is to anabolism as ________ is to ________.
B) exergonic; endergonic
45) 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.
32) The active site of an enzyme is the region that
B) is involved in the catalytic reaction of the enzyme.
49) Besides turning enzymes on or off, what other means does a cell use to control enzymatic activity?
B) localization of enzymes into specific organelles or membranes
17) Which of the following best describes enthalpy (H)?
B) the heat content of a chemical system
46) Which of the following statements describes enzyme cooperativity?
C) A substrate molecule bound to an active site of one subunit promotes substrate binding to the active site of other subunits.
25) A number of systems for pumping ions across membranes are powered by ATP. Such ATP-powered pumps are often called ATPases, although they don't often hydrolyze ATP unless they are simultaneously transporting ions. Because small increases in calcium ions in the cytosol can trigger a number of different intracellular reactions, cells keep the cytosolic calcium concentration quite low under normal conditions, using ATP-powered calcium pumps. For example, muscle cells transport calcium from the cytosol into the membranous system called the sarcoplasmic reticulum (SR). If a resting muscle cell's cytosol has a free calcium ion concentration of 10-7 while the concentration in the SR is 10-2, then how is the ATPase acting?
C) ATPase activity must be pumping calcium from the cytosol to the SR against the concentration gradient.
18) For the hydrolysis of ATP to ADP + ℗i, the free-energy change is —7.3 kcal/mol under standard conditions (1 M concentration of both reactants and products). In the cellular environment, however, the free-energy change is about —13 kcal/mol. What can we conclude about the free-energy change for the formation of ATP from ADP and ℗i under cellular conditions?
C) It is about +13 kcal/mol.
2) Which of the following is true for anabolic pathways?
C) They consume energy to build up polymers from monomers.
48) Which of the following is an example of cooperativity?
C) a molecule binding at one unit of a tetramer, allowing faster binding at each of the other three
21) Which of the following is most similar in structure to ATP?
C) an RNA nucleotide
44) How might an amino acid change at a site distant from the active site of the enzyme alter the enzyme's substrate specificity?
C) by changing the shape of the protein
41) When you have a severe fever, what grave consequence may occur if the fever is not controlled?
C) change in the tertiary structure of your enzymes
35) Increasing the substrate concentration in an enzymatic reaction could overcome which of the following?
C) competitive inhibition
43) In experimental tests of enzyme evolution, where a gene encoding an enzyme is subjected to multiple cycles of random mutagenesis and selection for altered substrate specificity, the resulting enzyme had multiple amino acid changes associated with altered substrate specificity. Where in the enzyme were these amino acid changes located?
C) in or near the active site and at surface sites away from the active site
65) Most cells cannot harness heat to perform work because
C) temperature is usually uniform throughout a cell.
29) 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.
68) Some bacteria are metabolically active in hot springs because
C) their enzymes have high optimal temperatures.
13) The mathematical expression for the change in free energy of a system is ΔG =ΔH - TΔS. Which of the following is correct?
C) ΔG is the change in free energy.
5) 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.
8) 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.
36) Which of the following is true of enzymes?
D) Enzymes increase the rate of chemical reaction by lowering activation energy barriers.
7) 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.
23) When chemical, transport, or mechanical work is done by an organism, what happens to the heat generated?
D) It is lost to the environment.
24) 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.
12) Which of the following is true of metabolism in its entirety in all organisms?
D) Metabolism consists of all the energy transformation reactions in an organism.
33) According to the induced fit hypothesis of enzyme catalysis, which of the these is correct?
D) The binding of the substrate changes the shape of the enzyme's active site.
11) Which of the following is an example of potential rather than kinetic energy?
D) a molecule of glucose
47) Allosteric enzyme regulation is usually associated with
D) an enzyme with more than one subunit.
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(n)
D) cofactor necessary for enzyme activity.
6) Whenever energy is transformed, there is always an increase in the
D) entropy of the universe.
34) Mutations that result in single amino acid substitutions in an enzyme
D) may change the enzyme's optimal temperature or optimal pH.
20) 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.
26) What is the difference (if any) between the structure of ATP and the structure of the precursor of the A nucleotide in RNA?
E) There is no difference.
14) A system at chemical equilibrium
E) can do no work.
1) Which term most precisely describes the cellular process of breaking down large molecules into smaller ones?
E) catabolism
30) Which of the following statements regarding enzymes is true?
enzymes increase the rate of a reaction by lowering the activation energy barrier
