Chapter 8 Study Questions
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:
+△G, +△H, -△S
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?
+△H, -△S, +△G
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
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. Which of the following statements describes enzyme cooperativity?
A substrate molecule bound to an active site affects the active site of several subunits.
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 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^-7while 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.
How can one increase the rate of a chemical reaction?
Add a catalyst.
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 create more disorder in their environment than the decrease in entropy associated with their growth.
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 is a statement of the first law of thermodynamics?
Energy cannot be created or destroyed.
Which of the following statements regarding enzymes is true?
Enzymes increase the rate of a reaction
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.
When ATP releases some energy, it also releases inorganic phosphate. What purpose does this serve (if any) in the cell?
It can be added to other molecules in order to activate them
When chemical, transport, or mechanical work is done by an organism, what happens to the heat generated?
It is lost to the environment
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?
Metabolism is a property of organismal life
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-dimensional change that opens another active site on the enzyme.
According to the induced fit hypothesis of enzyme catalysis, which of the following is correct?
The binding of the substrate depends on the shape of the active site
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 (are) true about enzyme-catalyzed reactions?
The reaction is faster than the same reaction in the absence of the enzyme.
Which of the following is true for all exergonic reactions?
The reaction proceeds with a net release of free energy
What must be 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 concerning catabolic pathways?
They are usually coupled with anabolic pathways to which they supply energy in the form of ATP
Which of the following is (are) true for anabolic pathways?
They consume energy to build up 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 both the reactants and products are only used in a metabolic pathway that is completely inactive
Which of the following is an example of potential rather than kinetic energy?
a food molecule made up of energy-rich macromolecules
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
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
Which of the following is most similar in structure to ATP?
an RNA nucleotide
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. Substance A functions as
an allosteric inhibitor.
Some enzymatic regulation is allosteric. In such cases, which of the following would usually be found?
an enzyme with more than one subunit
Which of the following is likely to lead to an increase in the concentration of ATP in a cell?
an increase in a cell's catabolic activity
Which of the following is considered an open system?
an organism
Sucrose is a disaccharide, composed of the monosaccharides glucose and fructose. The hydrolysis of sucrose by the enzyme sucrase results in
breaking the bond between glucose and fructose and forming new bonds from the atoms of water.
How does a noncompetitive inhibitor decrease the rate of an enzyme reaction?
by changing the shape of an enzyme
Which term most precisely describes the cellular process of breaking down large molecules into smaller ones?
catabolism
When you have a severe fever, what may be a grave consequence if this is not controlled?
change in the folding of enzymes
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.
Besides turning enzymes on or off, what other means does a cell use to control enzymatic activity?
compartmentalization of enzymes into defined organelles
Increasing the substrate concentration in an enzymatic reaction could overcome which of the following?
competitive inhibition
Which of the following types of reactions would decrease the entropy within a cell?
dehydration reactions
A chemical reaction that has a positive △G is correctly described as
endergonic.
What term is used to describe the transfer of free energy from catabolic pathways to anabolic pathways?
energy coupling
Whenever energy is transformed, there is always an increase in the
entropy of the universe.
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. The mechanism in which the end product of a metabolic pathway inhibits an earlier step in the pathway is known as
feedback inhibition.
The organization of organisms has become increasingly complex with time. This statement
is consistent with the second law of thermodynamics
The active site of an enzyme is the region that
is involved in the catalytic reaction of the enzyme
What is the change in free energy of a system at chemical equilibrium?
no net change
Competitive inhibitors block the entry of substrate into the active site of an enzyme. On which of the following properties of an active site does this primarily depend?
the ability of an enzyme to form a template for holding and joining molecules
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.
Among enzymes, kinases catalyze phosphorylation, while phosphatases catalyze removal of phosphate(s). A cell's use of these enzymes can therefore function as an on-off switch for various processes. Which of the following is probably involved?
the change in a protein's charge leading to a conformational change
Which of the following best describes enthalpy (H)?
the heat content of a chemical system
The mathematical expression for the change in free energy of a system is △G =△H-T△S. Which of the following is (are) correct?
△G is the change in free energy