Bio 121 Chapter 6+7
Which of the following combinations of products would result from three acetyl CoA molecules entering the citric acid cycle (see the figure)?
3 ATP, 3 CoA, 6 CO2, 9 NADH, and 3 FADH2
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:
+ (delta)G, + (delta)H, - (delta)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?
+ (delta)H, - (delta)S, + (delta)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
The ΔG for a particular enzyme-catalyzed reaction is -20 kcal/mol. If the amount of enzyme in the reaction is doubled, what will be the ΔG for the new reaction?
-20 kcal/mol
In a mitochondrion, if the matrix ATP concentration is high and there is no proton gradient across the inner mitochondrial membrane to generate a proton-motive force, then what might you expect to occur?
ATP synthase will hydrolyze ATP and pump protons into the intermembrane space.
Assuming glucose is the only energy source for a cell, what fraction of the carbon dioxide produced by aerobic respiration is generated by the reactions of the citric acid cycle?
2/3
The figure 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
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 an accurate description of the events that occur along the electron transport chain depicted in the figure?
Each electron transfer between carriers results in oxidation of one carrier and reduction of another.
In addition to ATP, what are the products of glycolysis?
NADH and pyruvate
Why does the oxidation of organic compounds by molecular oxygen to produce CO2 and water release free energy?
Electrons are moved from atoms that have a lower affinity for electrons (such as C) to atoms with a higher affinity for electrons (such as O)
The figure illustrates the electron transport chain. Which of the following is initially added to the chain with the highest free energy?
NADH
The figure 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
The figure 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 ΔG for the reaction?
D
The figure 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
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.
When 10,000 molecules of ATP are hydrolyzed to ADP and Pi 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 are not the same
A noncompetitive inhibitor decreases the rate of an enzymatic reaction by
changing the shape of the enzyme active site.
Under anaerobic conditions, what carbon sources can be metabolized by yeast cells to produce ATP from ADP?
glucose
Yeast cells with defective mitochondria are incapable of cellular respiration. Catabolism of which of the following energy sources would allow these to grow?
glucose
Which of the following indicates a primary path by which electrons travel downhill energetically during aerobic respiration?
glucose → NADH → electron transport chain → oxygen
Which of the following sequences represents the correct order in which metabolic reactions occur during the complete oxidation of glucose through aerobic respiration?
glucose → glycolysis → pyruvate oxidation → citric acid cycle → electron transport chain
Which of the following metabolic pathways is common to both aerobic cellular respiration and anaerobic fermentation?
glycolysis
Which of the following metabolic processes in eukaryotic cells will proceed normally whether oxygen (O2) is present or absent?
glycolysis
Which of the following metabolic pathways occur(s) in the cytosol of eukaryotic cells?
glycolysis and fermentation
Which of the following reactions release energy?
hydrolysis reactions
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
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
Enzymes are described as catalysts, which means that they
increase the rate of a reaction without being consumed by the reaction
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
The complete reactions of cellular respiration in the presence of oxygen (C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy) result in which of the following?
oxidation of C6H12O6 and reduction of O2
Which of the following metabolic pathways occur(s) in mitochondria?
oxidation of pyruvate to acetyl CoA and the citric acid cycle
Which of the following metabolic pathways requires a proton gradient?
oxidative phosphorylation
Which of the following metabolic processes produces the most ATP when glucose (C6H12O6) is completely oxidized to carbon dioxide (CO2) and water?
oxidative phosphorylation (chemiosmosis)
When a glucose molecule loses a hydrogen atom as the result of an oxidation-reduction reaction, the glucose molecule becomes
oxidized
Explain cellular respiration
oxygen + energy = carbon dioxide and water
An enzyme-catalyzed reaction is conducted in a test tube with a fixed amount of enzyme. Increasing the enzyme concentration in the test tube may overcome the effect of which of the following conditions?
presence of a fixed amount of a competitive inhibitor
Which of the following best describes enthalpy (H)?
the heat content of a chemical system
Anabolism requires what?
the input of energy
The mathematical expression for the change in free energy of a system is (delta)G = (delta)H-T (delta)S. Which of the following is correct?
(delta)G is the change in free energy.
Approximately what percentage of the ATP formed by the reactions of glycolysis is produced by substrate-level phosphorylation?
100%
If 30 molecules of ATP are produced for each molecule of glucose completely oxidized to carbon dioxide and water, how many ATP molecules will be produced for each molecule of pyruvate completely oxidized to carbon dioxide and water?
14
How many carbon atoms from one molecule of pyruvate enter the citric acid cycle?
2
Glycolysis results in a net production of which of the following molecules from each molecule of glucose?
2 NADH, 2 pyruvate, and 2 ATP
Which of the following correctly lists all of the energy-containing molecules produced by the catabolism of one molecule of glucose in glycolysis?
2 NADH, 2 pyruvate, and 2 ATP
For each mole of glucose (C6H12O6) completely oxidized by cellular respiration, how many moles of CO2 are released in the citric acid cycle (see the figure)?
4
In the complete oxidation of a molecule of glucose (C6H12O6) in aerobic cellular respiration, how many molecules of ATP are produced by substrate-level phosphorylation?
4
How many molecules of oxygen (O2) are consumed by the complete oxidation of glucose (C6H12O6) to carbon dioxide and water in aerobic respiration?
6
The complete oxidation of two molecules of glucose (C6H12O6) in cellular respiration produces about how many molecules of ATP?
60-64
Suppose that a cell's demand for ATP suddenly exceeds its supply of ATP from cellular respiration. Which statement correctly describes how this increased demand would lead to an increased rate of ATP production?
ATP levels would fall at first, decreasing the inhibition of PFK and increasing the rate of ATP production.
Brown fat cells produce a protein called thermogenin in their mitochondrial inner membrane. Thermogenin is an ion channel that facilitates diffusion of protons across the membrane. What will occur in the brown fat cells when thermogenin is present in their inner mitochondrial membranes?
ATP synthesis will decrease, and heat generation will increase.
A number of systems for pumping across membranes are powered by ATP. Such ATP-powered pumps are often called ATPases although they donʹt often hydrolyze ATP unless they are simultaneously transporting ions. Small increases in calcium ions in the cytosol trigger a number of different intracellular reactions, so the cells must keep the calcium concentration quite low. Muscle cells also transport calcium from the cytosol into the membranous system called the sarcoplasmic reticulum (SR). If a muscle cell cytosol has a free calcium ion concentration of 10-7 in a resting cell, while the concentration in the SR can be 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 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 would be unlikely to contribute to the substrate specificity of an enzyme?
Environmental factors such as temperature and pH.
Which of the following statements regarding enzymes is true?
Enzymes increase the rate of a reaction by lowering the activation energy barrier
Which of the following statements regarding enzymes is true?
Enzymes increase the rate of a reaction.
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 molecules donates electrons directly to the electron transport chain at the lowest energy level?
FADH2
During strenuous exercise, anaerobic conditions can result if the cardiovascular system cannot supply oxygen fast enough to meet the demands of muscle cells. Assume that a muscle cell's demand for ATP under anaerobic conditions remains the same as it was under aerobic conditions. What would happen to the cell's rate of glucose utilization?
Glucose utilization would increase a lot.
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.
Under anaerobic conditions (a lack of oxygen), the conversion of pyruvate to acetyl CoA stops. which is the correct explanation for this observation?
In the absence of oxygen, electron transport stops. NADH is no longer converted to NAD+, which is needed for the first three stages of cellular respiration.
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.
As a result of an oxidation-reduction reaction, how is the oxidizing agent changed?
It gains electrons and gains potential energy.
Which of the following statements is true for a molecule that is phosphorylated?
It has increased chemical potential energy that may be used to do cellular work.
In liver cells, the inner mitochondrial membranes are about five times the area of the outer mitochondrial membranes. What purpose must this serve?
It increases the surface area for oxidative phosphorylation.
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.
When chemical, transport, or mechanical work is done by an organism, what happens to the heat generated?
It is lost to the environment.
Upon completion of glycolysis, what is the fate of the majority of the potential energy contained in the original glucose molecule?
It is retained in two pyruvate molecules.
A glucose molecule is completely broken down to carbon dioxide and water in glycolysis and the citric acid cycle, but together these two processes yield only a few molecules of ATP. What happened to most of the energy that the cell obtains from the oxidation of glucose?
It is stored in NADH and FADH2
In an oxidation-reduction reaction, how is the reducing agent changed?
It loses electrons and loses potential energy.
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.
Why is ATP an important molecule in metabolism?
It provides energy coupling between exergonic and endergonic reactions.
Which of the following describes the process of glycolysis?
It represents the first stage in the chemical oxidation of glucose by a cell.
Select the correct statement about chemical energy, a term used by biologists to refer to potential energy available for release in a chemical reaction.
Light energy is converted to chemical energy during photosynthesis.
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 is a noncompetitive inhibitor.
Which of the following is the most comprehensive definition of metabolism in living organisms?
Metabolism consists of all the energy transformation reactions in an organism.
Which of the following is true of metabolism in its entirety?
Metabolism is a property of organismal life
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 of the following is NOT a way in which an enzyme can speed up the reaction that it catalyzes?
The active site can provide heat from the environment that raises the energy content of the substrate.
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 enzymeʹs active site.
The binding of a compound to an enzyme is observed to slow down or stop the rate of the reaction catalyzed by the enzyme. Increasing the substrate concentration reduces the inhibitory effects of this compound. Which of the following could account for this observation?
The compound is a competitive inhibitor.
Which of the following statements about the role of ATP in cell metabolism is true?
The energy from the hydrolysis of ATP may be directly coupled to endergonic processes by the transfer of the phosphate group to another molecule.
Which of the following statements about the combustion of glucose with oxygen to form water and carbon dioxide (C6H12O6 + 6 O2 → 6 CO2 + 6 H2O) is correct?
The entropy of the products is greater than the entropy of the reactants.
What is the free energy change (ΔG) of the hydrolysis of ATP to ADP?
The free-energy change (ΔG) of the hydrolysis of ATP to ADP and Pi may vary considerably with variations in pH, temperature, atmospheric pressure, and concentrations of reactants and products.
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.
Which one of the following statements about the redox reactions of the electron transport chain is correct?
The redox reactions of the electron transport chain are directly coupled to the movement of protons across a membrane.
Which of the following statements about a system at chemical equilibrium is true?
The system can do no work.
What must be the difference (if any) between the structure of ATP and the structure of the precursor of the A nucleotide in DNA and 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 is true for anabolic pathways?
They consume energy to build up polymers from monomers.
Why are carbohydrates and fats considered high-energy foods?
They have a large number of electrons associated with hydrogen.
Which statement about the binding of enzymes and substrates is correct?
When substrate molecules bind to the active site of the enzyme, the enzyme undergoes a slight change in shape.
The process of cellular respiration, which converts simple sugars such as glucose into CO2 and water, is an example of
a catabolic pathway
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
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.
Which of the following is an example of potential rather than kinetic energy?
a food molecule made up of energy-rich macromolecules
In the complete reactions of aerobic respiration, the energy for most of the ATP produced is provided by
a proton gradient across a membrane.
An enzyme-catalyzed reaction is conducted in a test tube with a fixed amount of enzyme. Increasing the enzyme concentration in the test tube may overcome the effect of which of the following conditions?
a saturated enzyme population
Describe the metabolic pathway
a series of metabolic reactions within an initial substrate and a final product. The product of one reaction becomes the substrate for the subsequent reaction.
The free-energy change for the hydrolysis of ATP to ADP + Pi, 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 Pi) would be under cellular conditions?
about +13 kcal/mol
The oxygen consumed during cellular respiration is involved directly in which process or event?
accepting electrons at the end of the electron transport chain
In the presence of oxygen, the pyruvate can be catabolized in the citric acid cycle. First, however, the pyruvate (1) loses a carbon, (2) is oxidized to form a two-carbon compound, which (3) is covalently bound to coenzyme A. These three steps result in the formation of
acetyl CoA, NADH, H+, and CO2.
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.
Reactants capable of interacting to form products in a chemical reaction must first overcome a thermodynamic barrier known as the reactionʹs
activation energy.
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
In addition to its critical role in cellular metabolism, ATP may also be described as which of the following?
an RNA nucleotide
Which of the following is most similar in structure to ATP?
an RNA nucleotide
Which kind of metabolic poison would most directly interfere with glycolysis?
an agent that closely mimics the structure of glucose but is not metabolized
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
An organism's metabolism transforms
matter and energy
The synthesis of ATP by oxidative phosphorylation, using the energy released by movement of protons across the membrane down their electrochemical gradient, is an example of
an endergonic reaction coupled to an exergonic reaction.
Energy transformations in organisms are always associated with
an increase in the entropy of the universe.
Which of the following is considered an open system?
an organism
Which of the following types of reactions would decrease the entropy within a cell?
anabolic reactions
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.
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.
Which of the following terms describes metabolic pathways that break down complex molecules to release stored energy?
catabolic pathways
The cellular process of breaking down large molecules into smaller ones is defined as
catabolism
Which term most precisely describes the cellular process of breaking down large molecules into smaller ones?
catabolism
Metabolism as a whole manages the material and energy of the
cell
Which of the protein complexes labeled with Roman numerals in the figure transfers electrons to O2?
complex IV
Which temperature and pH profile curves on the graphs in the figure were most likely generated from analysis of an enzyme from a human stomach, where conditions are strongly acidic?
curves 1 and 4
Where does glycolysis occur in animal cells?
cytosol
Which of the following types of reactions would decrease the entropy within a cell?
dehydration reactions
A chemical reaction that has a positive ΔG is best described as
endergonic
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
In chemiosmosis, what is the most direct source of energy that is used to convert ADP + Pi to ATP?
energy released from movement of protons down their electrochemical gradient through ATP synthase
Whenever energy is transformed, there is always an increase in the
entropy of the universe.
The mechanism by which the end product of a metabolic pathway inhibits an enzyme that catalyzes an earlier step in the pathway is most precisely described as
feedback inhibition.
Where in mitochondria is the enzyme ATP synthase localized?
inner membrane
Where are the proteins of the electron transport chain located in a eukaryotic cell?
inner mitochondrial membrane
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.
The totality of an organism's chemical reactions is called
metabolism
Which organelles or organisms are capable of synthesizing ATP using energy from chemiosmosis?
mitochondria, chloroplasts, and bacteria that generate proton gradients across their plasma membranes
Energy released by the electron transport chain is used to pump H+ into which location in eukaryotic cells?
mitochondrial intermembrane space
The oxygen atoms used to form water in the complete reactions of cellular respiration are derived from which of the following molecules?
molecular oxygen (O2)
What is the change in free energy of a system at chemical equilibrium?
no net change
Which of the following processes would be an example of a catabolic pathway?
providing energy that can be used to drive cellular work
Cells use the ATP cycle shown in the figure to perform which of the following processes?
recycle ADP and phosphate
What is the source of the energy used to generate the proton gradient across the inner mitochondrial membrane?
redox reactions in the electron transport chain
When a molecule of NAD+ (nicotinamide adenine dinucleotide) gains a hydrogen atom (not a proton), the NAD+ molecule becomes
reduced.
During alcohol fermentation in yeast, NAD+ is regenerated from NADH by which of the following processes?
reduction of acetaldehyde to ethanol
Catabolism is the process during which energy is
released
Which chemical process generates the ATP produced in the citric acid cycle?
substrate-level phosphorylation
Which of the following processes is responsible for the ATP made during fermentation?
substrate-level phosphorylation
Most cells cannot harness heat to perform work because
temperature is usually uniform throughout a cell
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.
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.
Energy is observed in two basic forms: potential and kinetic. Which of the following correctly matches these forms with a source of energy?
the covalent bonds of a sugar molecule: potential energy
When hydrogen ions are pumped from the mitochondrial matrix across the inner membrane and into the intermembrane space, the result is
the creation of a proton-motive force.
Which of the following metabolic pathways generates a proton gradient?
the electron transport chain
What is the immediate source of the energy used to synthesize ATP by oxidative phosphorylation in eukaryotic cells?
the proton-motive force across the inner mitochondrial membrane
Which of the following statements describes a primary function of both alcohol fermentation and lactic acid fermentation?
to oxidize NADH to NAD+
Which of the following is the most important result of the process of cellular respiration in biological systems?
transforming the energy in glucose and related molecules in a chemical form that cells can use for work
In the absence of oxygen, what is the net gain of ATP for each glucose molecule that enters glycolysis?
two ATP
The electrons stripped from glucose in cellular respiration end up in which compound?
water
Carbon skeletons for amino acid biosynthesis are supplied by intermediates of the citric acid cycle (see the figure). Which intermediate would you predict may directly supply the carbon skeleton for synthesis of a five-carbon amino acid?
α-ketoglutarate
