CH 8
Which of the following is the most correct interpretation of the figure?
ATP is a molecule that acts as an intermediary to store energy for cellular work.
A number of systems for pumping ions across membranes are powered by ATP. Such ATP- powered pumps are often called ATPases, although they do not 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?
ATPase activity must be pumping calcium from the cytosol to the SR against the concentration gradient.
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.
Based on this information, which of the following is correct?
Succinate is the substrate, and fumarate is the product.
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.
Reactants capable of interacting to form products in a chemical reaction must first overcome a thermodynamic barrier known as the reaction's _____.
activation energy
Which of the following is most similar in structure to ATP?
an RNA nucleotide
With respect to the enzyme that converts X to Y, substance A functions as _____.
an allosteric inhibitor
Allosteric enzyme regulation is usually associated with _____.
an enzyme with more than one subunit
Which of the following types of reactions would decrease the entropy within a cell?
anabolic reactions
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
Which term most precisely describes the cellular process of breaking down large molecules into smaller ones?
catabolism (catabolic pathways)
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
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?
curves 1 and 4
Which curves on the graphs 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?
curves 3 and 5
Which of the following in the figure would be the same in either an enzyme-catalyzed or a noncatalyzed reaction?
d
Which of the following represents the activation energy required for the enzyme-catalyzed reaction in the figure?
B
What is substance X?
a substrate
A system at chemical equilibrium _____.
can do no work
Which of the following involves a decrease in entropy?
condensation reactions
Catabolic pathways _____.
supply energy, primarily in the form of ATP, for the cell's work
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
-20 kcal/mol
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.
How do cells use the ATP cycle shown in the figure?
Cells use the cycle to recycle ADP and phosphate.
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 a statement of the first law of thermodynamics?
Energy cannot be created or destroyed.
Which of the following is true of enzymes?
Enzymes increase the rate of chemical reaction by lowering activation energy barriers.
Which of the following statements is a logical consequence of the second law of thermodynamics?
Every chemical reaction must increase the total entropy of the universe.
In solution, why do hydrolysis reactions occur more readily than condensation reactions?
Hydrolysis increases entropy and is exergonic.
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.
Which of the following is true of metabolism in its entirety in all organisms?
Metabolism consists of all the energy transformation reactions in an organism.
In the 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
Reactant and product concentrations in the test tube are different from those in the cell.
In a biological reaction, succinate dehydrogenase catalyzes the conversion of succinate to fumarate. The reaction is inhibited by malonic acid, a substance that resembles succinate but cannot be acted upon by succinate dehydrogenase. Increasing the amount of succinate molecules to those of malonic acid reduces the inhibitory effect if malonic acid. Select the correct identification of the molecules described in the reaction.
Succinate is the substrate, and fumarate is the product in the reaction.
Biological systems use free energy based on empirical data that all organisms require a constant energy input. The first law of thermodynamics states that energy can be neither created nor destroyed. For living organisms, which of the following statements is an important consequence of this first law?
The organism must ultimately obtain all the necessary energy for life from its environment.
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 is true for all exergonic reactions?
The reaction proceeds with a net release of free energy.
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?
They can more readily encounter and phosphorylate other membrane proteins.
Chemical equilibrium is relatively rare in living cells. An example of a reaction at chemical equilibrium in a cell would be _____.
a chemical reaction in which both the reactants and products are not being produced or used in any active metabolic pathway at that time in the cell
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 cofactor necessary for enzyme activity
Which of the following is an example of cooperativity?
a molecule binding at one unit of a tetramer, allowing faster binding at each of the other three
Which of the following is an example of potential rather than kinetic energy?
a molecule of glucose
For the enzyme- catalyzed reaction shown in the figure, if the initial reactant concentration is 1.0 micromolar, which of these treatments will cause the greatest increase in the rate of the reaction?
doubling the enzyme concentration
A chemical reaction that has a positive ΔG is best described as _____.
endergonic
Which of the following terms best describes the forward reaction in the figure?
exergonic, ∆G < 0
Choose the pair of terms that correctly completes this sentence: Catabolism is to anabolism as _____ is to _____.
exergonic; endergonic
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
What is malonic acid's role with respect to succinate dehydrogenase? Malonic acid _____.
is a competitive inhibitor
The active site of an enzyme is the region that _____.
is involved in the catalytic reaction of the enzyme
Besides turning enzymes on or off, what other means does a cell use to control enzymatic activity?
localization of enzymes into specific organelles or membranes
Most cells cannot harness heat to perform work because _____.
temperature is usually uniform throughout a cell
According to the induced fit hypothesis of enzyme catalysis, _____.
the binding of the substrate changes the shape of the enzyme's active site
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.
