EXAM 4- Chapter 8
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?
-20 kcal/mol
The following question is based on the reaction A + B ↔ C+ D shown in the accompanying figure. Which of the following represents the activation energy needed for the enzyme-catalyzed reverse reaction, C + D → A + B, in the figure?
A
Which of the following is the most correct interpretation of the accompanying figure?
ATP is a molecule that acts as an intermediary to store energy for cellular work.
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?
As a consequence of growing, organisms cause a greater increase in entropy in their environment than the decrease in entropy associated with their growth.
The following question is based on the reaction A + B ↔ C+ D shown in the accompanying figure. Which of the following represents the activation energy required for a noncatalyzed reaction in the figure?
C
Which of the following statements is representative of the second law of thermodynamics?
Cells require a constant input of energy to maintain their high level of organization.
The following question is based on the reaction A + B ↔ C + D shown in the accompanying figure. Which of the following in the figure would be the same in either an enzyme-catalyzed or a noncatalyzed reaction?
D
The following question is based on the reaction A + B ↔ C + D shown in the accompanying figure. Which of the following in the figure would be the same in either an enzyme-catalyzed or a noncatalyzed reaction?
D
The following question is based on the reaction A + B ↔ C+ D shown in the accompanying figure. 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?
D
The following question is based on the reaction A + B ↔ C+ D shown in the accompanying figure. Which of the following represents the activation energy needed for the noncatalyzed reverse reaction, C + D → A + B, in the figure?
E
You have discovered an enzyme that can catalyze two different chemical reactions. Which of the following is most likely to be correct?
Either the enzyme has two distinct active sites or the reactants involved in the two reactions are very similar in size and shape.
Which of the following is TRUE of enzymes?
Enzymes increase the rate of chemical reaction by lowering activation energy to the substrate.
When chemical, transport, or mechanical work is done by an organism, what happens to the heat generated?
It is lost to the environment.
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?
It is probably an enzyme that works through allosteric regulation.
When ATP releases some energy, it also releases inorganic phosphate. What happens to the inorganic phosphate in the cell?
It may be used to form a phosphorylated intermediate.
Why is ATP an important molecule in metabolism?
It provides energy coupling between exergonic and endergonic reactions.
Rate of an enzyme-catalyzed reaction as a function of varying reactantconcentration, with the concentration of enzyme constant. In the accompanying figure, why does the reaction rate plateau at higher reactant concentrations?
Most enzyme molecules are occupied by substrate at high reactant concentrations.
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?
Reactant and product concentrations in the test tube are different from those in the cell.
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?
The binding of the two molecules must cause a 3-D change in the enzyme.
Which of the following is TRUE when comparing an uncatalyzed reaction to the same reaction with a catalyst?
The catalyzed reaction will have the same ∆G.
For living organisms, which of the following is an important consequence of the first law of thermodynamics?
The organism ultimately must obtain all of the necessary energy for life from its environment.
Which of the following statements is TRUE about enzyme-catalyzed reactions?
The reaction is faster than the same reaction in the absence of the enzyme.
Which of the following is an example of potential rather than kinetic energy?
a molecule of glucose
Use the following information to answer the question(s) below. 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 substrate
Reactants capable of interacting to form products in a chemical reaction must first overcome a thermodynamic barrier known as the reaction's ________.
activation energy
Use the following information to answer the question(s) below. 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 ________.
an allosteric inhibitor
The lock-and-key analogy for enzymes applies to the specificity of enzymes ________.
binding to their substrate
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?
by changing the shape of an enzyme
A system at chemical equilibrium ________.
can do no work
A noncompetitive inhibitor decreases the rate of an enzyme reaction by ________.
changing the shape of the enzyme's active site
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?
competitive inhibition
Increasing the substrate concentration in an enzymatic reaction could overcome which of the following?
competitive inhibition
Anabolic pathways ________.
consume energy to build up polymers from monomers
A chemical reaction that has a positive ΔG is best described as ________.
endergonic
The following question is based on the reaction A + B ↔ C + D shown in the accompanying figure. Which of the following terms best describes the forward reaction in the figure?
exergonic, ∆G < 0
The mechanism in which the end product of a metabolic pathway inhibits an earlier step in the pathway is most precisely described as ________.
feedback inhibition
Biological evolution of life on Earth, from simple prokaryote-like cells to large, multicellular eukaryotic organisms, ________.
has occurred in accordance with the laws of thermodynamics
You collect data on the effect of pH on the function of the enzyme catalase in human cells. Which of the following graphs would you expect?
hill graph
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?
in or near the active site
Enzymes ________.
increase the rate of a reaction by lowering the activation energy barrier
Catabolic pathways ________.
supply energy, primarily in the form of ATP, for the cell's work
A solution of starch at room temperature does NOT readily decompose to form a solution of simple sugars because ________.
the activation energy barrier for this reaction cannot easily be surmounted at room temperature
According to the induced fit hypothesis of enzyme catalysis, ________.
the binding of the substrate changes the shape of the enzyme's active site
Some bacteria are metabolically active in hot springs because ________.
their enzymes have high optimal temperatures
Enthalpy (H) is the ________.
total energy in biological systems
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?
water solubility
The mathematical expression for the change in free energy of a system is ΔG=ΔH − TΔS. Which of the following is (are) correct?
ΔG is the change in free energy.
