BIO 111 General Biology Chapter 6 (Mastering Biology)
Which of the following processes would be an example of a catabolic pathway?
providing energy that can be used to drive cellular work
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.
A noncompetitive inhibitor decreases the rate of an enzymatic reaction by
changing the shape of the enzyme active site.
The free-energy change for the hydrolysis of ATP to ADP + ℗ i, under standard conditions (1 M concentration of both reactants and products) is -7.3 kcal/mol. However, in the cytoplasm of the cell, the free-energy change is about -13 kcal/mol. Based on this observation, what would you predict the free-energy change for the reverse reaction (formation of ATP from ADP and ℗ i) would be under cellular conditions?
about +13 kcal/mol
In most exergonic reactions, before products can be formed, the reactants must first overcome a thermodynamic barrier known as the
activation energy of the reaction.
A series of enzymes catalyze the reactions illustrated in the following metabolic pathway: 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 of A decreases the activity of the enzyme that converts X to Y. The product A functions as which of the following in terms of its effect on the enzyme that converts X to Y?
an allosteric inhibitor
Energy transformations in organisms are always associated with
an increase in the entropy of the universe.
Which of the following types of reactions would decrease the entropy within a cell?
anabolic reactions
The cellular process of *SYNTHESIZING* large molecules from smaller ones is defined as
anabolism.
Cooperativity is a form of allosteric activation in which
binding of a substrate molecule to one active site in a multisubunit enzyme stimulates the binding of substrate molecules to the active sites of other subunits.
A mutation results in an amino acid substitution at a site distant from the active site of an enzyme. How might this amino acid change alter the active site and substrate specificity of the enzyme?
by changing the conformation of the enzyme
The cellular process of breaking down large molecules into smaller ones is defined as
catabolism.
The activity of many cellular enzymes is regulated by activators and inhibitors. Enzyme activity is also regulated in eukaryotic cells by which of the following mechanisms?
compartmentalization and restricting enzymes to specific organelles or membranes
Which temperature and pH profile curves on the graphs in Figure 6.3 were most likely generated from analysis of an enzyme from a human stomach, where conditions are strongly acidic?
curves 1 and 4
Which curves on the graphs in Figure 6.3 may represent the temperature and pH profiles of an enzyme taken from a bacterium that lives in a mildly alkaline hot spring at temperatures of 70°C or higher?
curves 3 and 5
Which of the following reactions tend to require an input of energy?
dehydration
Figure 6.4 illustrates various aspects of the free-energy change (ΔG) for the reaction A + B ↔ C + D. Which of the following changes in free-energy represents the overall Δ G for the reaction?
e
Figure 6.4 illustrates various aspects of the free-energy change (ΔG) for the reaction A + B ↔ C + D. Which of the following best describes the forward reaction?
exergonic, G< 0
Choose the pair of terms that correctly completes this sentence: Catabolism is to anabolism as ________ is to ________.
exergonic; endergonic
Which of the descriptions below is an example of an exergonic reaction?
hydrolysis of glycogen to release glucose monomers
Which of the following reactions release energy?
hydrolysis reactions
In experimental tests of enzyme evolution, a gene encoding an enzyme was subjected to multiple cycles of random mutagenesis and selection for altered substrate specificity. The resulting enzyme with altered substrate specificity had multiple amino acid changes. Where in the enzyme might these amino acid changes be located?
in or near the active site, in the hydrophobic interior, and/or at surface sites distant from the active site
Under a particular set of conditions in the lab, the enzyme in a chemical reaction is saturated. Which of the following alterations to the reaction will increase the rate at which substrate is converted to product?
increasing the amount of enzyme in the reaction
A solution of starch at room temperature does not readily decompose to form a solution of glucose because
the activation energy barrier for this reaction cannot easily be overcome at room temperature.
Which of the following descriptions would be an example of potential energy?
the chemical bonds in a molecule of sucrose
The ∆ G for a particular enzyme-catalyzed reaction is -20 kcal/mol. If the enzyme is removed, what will be the ∆ G for the noncatalyzed reaction?
-20 kcal/mol
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.
Which of the following is a statement of the first law of thermodynamics?
Energy cannot be created or destroyed.
Which of the following statements is true of enzymes?
Enzymes increase the rate of chemical reactions by lowering activation energy barriers.
An aminoacyl-tRNA synthetase is the enzyme that catalyzes the attachment of a particular amino acid to its corresponding tRNA. This reaction requires energy from ATP. The enzyme initially binds the amino acid and ATP, but it is unable to bind the tRNA at this point. Which of the following would be a likely next step in the reaction by which the enzyme ultimately binds the tRNA and attaches the amino acid?
Hydrolysis of ATP phosphorylates the amino acid, which results in a conformational change in the active site that allows the tRNA to bind.
Hydrolysis of ATP releases energy, which ultimately results in the production of ADP and inorganic phosphate. What is commonly the immediate fate of the phosphate released by ATP hydrolysis in the cell?
It is attached to a substrate to form a phosphorylated intermediate.
Hydrolysis of ATP releases energy, which ultimately results in the production of ADP and inorganic phosphate. What generally happens to the inorganic phosphate produced in the cytosol?
It is combined with ADP to regenerate ATP
A mutation that results in a single amino acid substitution in the active site of an enzyme may have which of the following consequences?
It may alter the ability of a noncompetitive inhibitor to bind to the enzyme.
Why might a severe fever result in death if it is not brought under control?
It may increase the rate of cellular chemical reactions.
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. The effect of malonic acid on the activity of succinate dehydrogenase suggests which of the following?
Malonic acid blocks the binding of fumarate
Which of the following is the most comprehensive definition of metabolism in living organisms?
Metabolism manages the increase of entropy in an organism.
In Figure 6.2, why does the reaction rate plateau at higher reactant concentrations?
Most enzyme molecules are occupied by substrate at high reactant concentrations.
If an enzyme is added to a solution in which its substrate and product are in equilibrium, what will occur?
Nothing; the reaction will stay at equilibrium.
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. Which of the following statements regarding the molecules involved in this reaction is correct?
Succinate is the substrate, and fumarate is the product.
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 which of the following is the most likely mechanism by which the muscle cell ATPase maintains intracellular calcium concentrations?
The ATPase pumps calcium from the cytosol into the SR against the concentration gradient.
Which of the following statements best describes the induced fit model of enzyme activity?
The binding of substrate changes the conformation of the active site to bind substrate more tightly.
Based on the first law of thermodynamics, which of the following statements about a living organism is true?
The organism ultimately must obtain all of the necessary energy for life from its environment.
What is the difference (if any) between the structure of ATP and the structure of the A nucleoside triphosphate used to make *DNA*?
The sugar molecule is different.
Which of the following statements about a system at chemical equilibrium is true?
The system can do no work.
Anabolic pathways share which of the following characteristics?
They consume energy to synthesize polymers from monomers.
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 neither the reactants nor the products are being produced or used in any other active metabolic pathway at that time in the cell
An enzyme-catalyzed reaction is conducted in a test tube with a fixed amount of enzyme. Increasing the substrate concentration in the test tube may overcome the effect of which of the following conditions?
a saturated enzyme population
Which of the following is an example of an anabolic pathway?
a set of reactions that combine monomers into larger, more energy-rich polymers
Which of the following is the most correct interpretation of Figure 6.1?
ATP is a molecule that acts as an intermediary to store energy for cellular work.
Which of the following statements best describes the critical role that ATP plays in cellular metabolism?
ATP serves as an energy shuttle in the cell, coupling exergonic and endergonic reactions.
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.
When chemical, transport, or mechanical work is performed by an organism, what happens to the heat that is generated?
It is released to the environment.
A mutation that alters a single amino acid in a region of the enzyme outside of the active site may result in which of the following consequences?
It may alter an allosteric site on the enzyme.
ATP hydrolysis in a test tube releases only about half as much energy as ATP hydrolysis in the cell. Which of the following statements is the best explanation for this observation?
Reactant and product concentrations in the cell are different from the standard conditions used in a test tube.
Which of the following statements about enzyme-catalyzed reactions is true?
The rate of the reaction is greater than when the same reaction occurs in the absence of an enzyme.
What is the difference (if any) between the structure of ATP and the structure of the A nucleoside triphosphate used to make *RNA*?
There is no difference; they are the same molecule.
In addition to its critical role in cellular metabolism, ATP may also be described as which of the following?
an RNA nucleotide
Figure 6.4 illustrates various aspects of the free-energy change (ΔG) for the reaction A + B ↔ C + D. Which of the following changes in free-energy represents the activation energy *REQUIRED*for the enzyme-catalyzed reaction?
b
Figure 6.4 illustrates various aspects of the free-energy change (ΔG) for the reaction A + B ↔ C + D. Which of the following changes in free-energy represents the activation energy required for a noncatalyzed reaction?
c
Figure 6.4 illustrates various aspects of the free-energy change (ΔG) for the reaction A + B ↔ C + D. Which of the following changes in free-energy represents the difference between the free-energy content of the reactants and the free-energy content of the products?
d
Figure 6.4 illustrates various aspects of the free-energy change (ΔG) for the reaction A + B ↔ C + D. Which of the following changes in free-energy would be the same in either an enzyme-catalyzed or a noncatalyzed reaction?
d
Figure 6.4 illustrates various aspects of the free-energy change (ΔG) for the reaction A + B ↔ C + D. Which of the following represents change in free-energy for the reverse reaction, C + D → A + B?
d
For the enzyme-catalyzed reaction shown in Figure 6.2, 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
Cells use the ATP cycle shown in Figure 6.1 to perform which of the following processes?
recycle ADP and phosphate
Most cells cannot harness heat to perform work because:
temperature is usually uniform throughout a cell.
