Which term most precisely describes the cellular process of breaking down large molecules into smaller ones?
Which of the following is (are) true for anabolic pathways?
they consume energy to build up polymers from monomers
Which of the following is a statement of the first law of thermodynamics?
energy cannot be created or destroyed
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
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
Whenever energy is transformed, there is always an increase in the
entropy of the universe
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
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
Which of the following types of reactions would decrease the entropy within a cell?
Biological evolution of life on Earth, from simple prokaryote-like cells to large, multicellar eukaryotic organisms,
has occurred in accordance with the laws of thermodynamics
Which of the following is an example of potential rather than kinetic energy?
a molecule of glucose
Which of the following is the smallest closed system?
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
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
A system at chemical equilibrium
can do no work
Which of the following is true for all exergonic reactions?
the reaction proceeds with a net release of free energy
Chemical equilibrium is relatively rare in living cells. Which of the following could be an example of a reaction at chemical equilibrium in a cell?
a chemical reaction in which both the reactants and products are not being produced or used in any active metabolic pathway
Which of the following shows the correct changes in thermodynamic properties for a chemical reaction in which amino acids are linked to form a protein?
+ΔH, -ΔS, +ΔG
When glucose monomers are joined together by glycosidic linkages to form a cellulose polymer, the changes in free energy, total energy, and entropy are as follows:
+ΔG, +ΔH, -ΔS
A chemical reaction that has a positive ΔG is correctly described as
Which of the following best describes enthalpy (H)
the heat content of a chemical system
For the hydrolysis of ATP to ADP +(p) 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 (p) i under cellular conditions?
it is about +13 kcal/mol
Why is ATP an important molecule in metabolism?
it provides energy coupling between exergonic and endergonic reactions
When 10,000 molecules of ATP are hydrolyzed to ADP and (p) i in a test tube, about twice 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
Which of the following is most similar in structure to ATP?
an RNA nucleotide
Which of the following statements is true concerning catabolic pathways?
they 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?
it is lost to the environment
When ATP releases some energy, it also releases inorganic phosphate. What purpose does this serve (if any) in the cell?
the phosphate may be incorporated into any molecule that contains phosphate
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?
ATPase activity must be pumping calcium from the cytosol to the SR against the concentration gradient
What is the difference (if any) between the structure of ATP and the structure of the precursor of the A nucleotide in RNA?
there is no difference
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
Reactants capable of interacting to form products in a chemical reaction must first overcome a thermodynamic barrier known as the reaction's
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 be surmounted
Which of the following statements regarding enzymes is true?
enzymes 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?
The active site of an enzyme is the region that
is involved in the catalytic reaction of the enzyme
According to the induced fit hypothesis of enzyme catalysis, which of the following is correct?
the binding of the substrate changes the shape of the enzyme's active site
Mutations that result in single amino acid substitutions in an enzyme
may affect the physicochemical properties of the enzyme such as its optimal temperature and pH
Increasing the substrate concentration in an enzymatic reaction could overcome which of the following?
Which of the following is true of enzymes?
enzymes increase the rate of chemical reaction by lowering activation energy barriers
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)
cofactor necessary for enzyme activity
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?
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?
in or near the active site
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
When you have a severe fever, what grave consequence may occur if the fever is not controlled?
change in the tertiary structure of your enzymes
How does a noncompetitive inhibitor decrease the rate of an enzyme reaction?
by changing the shape of the enzyme's active site
The mechanism in which the end product of a metabolic pathway inhibits an earlier step in the pathway is most precisely described as
Which of the following statements describes enzyme cooperativity?
a substrate molecule bound to an active site of one subunit promotes substrate binding to the active site of other subunits
Allosteric enzyme regulation is usually associated with
an enzyme with more than one subunit
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
Protein kinases are enzymes that catalyze phosphorylation of target proteins at specific sites, whereas protein phosphatases catalyze removal of phosphate(s) from phosphorylated proteins. Phosphorylation and dephosphorylation can function as an on-off switch for a protein's activity, most likely through
the change in a protein's charge leading to a conformational change
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
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?
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?
in or near the active site and at surface sites away from the active site
How might an amino acid change at a site distant from the active site of the enzyme alter the enzyme's substrate specificity?
by changing the shape of the protein
For the enzyme-catalyzed reaction shown in the figure, which of these treatments will cause the greatest increase in the rate of the reaction, if the initial reactant concentration is 1.0 micromolar?
doubling the enzyme concentration
In the figure, why does the reaction rate plateau at higher reactant concentrations?
most enzyme molecules are occupied by substrate at high reactant concentrations
Which curve(s) 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 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 of the following terms best describes the forward reaction in Figure 8.1?
exergonic, ∆G < 0
Which of the following represents the ΔG of the reaction in Figure 8.1?
Which of the following in Figure 8.1 would be the same in either an enzyme-catalyzed or a noncatalyzed reaction?
Which of the following represents the activation energy needed for the enzyme-catalyzed reverse reaction, C + D → A + B, in Figure 8.1?
Which of the following represents the difference between the free-energy content of the reaction and the free-energy content of the products in Figure 8.1?
Which of the following represents the activation energy required for the enzyme-catalyzed reaction in Figure 8.1?
Which of the following represents the activation energy required for a noncatalyzed reaction in Figure 8.1?
Which of the following represents the activation energy needed for the noncatalyzed reverse reaction, C + D → A + B, in Figure 8.1?
Assume that the reaction in Figure 8.1 has a ΔG of -5.6 kcal/mol. Which of the following would be true?
the reaction would result in an increase in entropy (S) and a decrease in the total energy content (H) of the system
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
How do cells use the ATP cycle shown in the figure?
cells use the cycle to recycle ADP and phosphate
Succinate dehydrogenase catalyzes the conversion of succinate to fumarate. The reaction is inhibited by malonic acid, which resembles succinate but cannot be acted upon by succinate dehydrogenase. Increasing the ratio of succinate to malonic acid reduces the inhibitory effect of malonic acid. Based on this information, which of the following is correct?
succinate is the substrate, and fumarate is the product
What is malonic acid's role with respect to succinate dehydrogenase?
it is a competitive inhibitor
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?
With respect to the enzyme that converts X to Y, substance A functions as
an allosteric inhibitor
Choose the pair of terms that correctly completes this sentence: Catabolism is to anabolism as ________ is to ________.
Most cells cannot harness heat to perform work because
temperature is usually uniform throughout a cell
Which of the following metabolic processes can occur without a net influx of energy from some other process?
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O
If an enzyme in solution is saturated with substrate, the most effective way to obtain a faster yield of products is to
add more of the enzyme
Some bacteria are metabolically active in hot springs because
their enzymes have high optimal temperatures
If an enzyme is added to a solution where its substrate and product are in equilibrium, what will occur?
nothing; the reaction will stay at equilibrium