Biology Chapter 9
This step yields acetyl CoA and one molecule of NADH.
The oxidation of pyruvate to acetate and its subsequent conversion to acetyl CoA is the link between glycolysis and all the other reactions of cellular respiration.
Pathway taken when oxygen is unavailable
When oxygen is unavailable, pyruvate oxidation, the citric acid cycle, and the respiratory chain do not function, and the pyruvate produced by glycolysis is further metabolized by fermentation.
Catabolic interconversion is a metabolic pathway in which
a large molecule is broken down into its constituent molecules and releases energy.
Portion of pathway releasing the greatest total amount of energy
citric acid cycle and respiratory chain produce the most energy in cellular respiration.
The synthesis of ATP from ADP and Pi is an _______ reaction. In mitochondria, ATP synthesis is driven by the flow of _______ down a concentration gradient established by _______.
endergonic; protons; electron transport
Identify the region where hydrogen ions are concentrated
Identify the region where hydrogen ions are concentrated
If 0.5 mole of glucose is oxidized by lactic acid fermentation, the amount of ATP generated in the cytosol will be
1.0 mole.
Which is a viable path that a carbon atom could take as it moves through metabolic pathways in a cell?
Amino acid → purine → DNA → purine → amino acid → acetyl CoA → fatty acid → triglyceride
How should the y (vertical) axis be labeled?
Free energy relative to O2 (kcal/mole)
Which describes how the components of the respiratory chain are ordered?
From high to low reduction potential relative to oxygen
What is an example of anabolic interconversion?
Gluconeogenesis
Which statement could be used as part of a description of how carbohydrate, lipid, and protein are linked through catabolic and anabolic pathways?
Glycolysis and the citric acid cycle occupy a central position in cell metabolism, connecting to lipid, protein, and carbohydrate breakdown and synthesis through small molecule intermediates.
Which sequence of metabolic paths could a carbon atom take to go from a molecule of glucose to a molecule of DNA?
Glycolysis → pyruvate oxidation → citric acid cycle → amino acid biosynthesis → purine biosynthesis
A student made this table as a study guide for learning the various catabolic pathways that cells use for harvesting energy from glucose. Which statement best evaluates the accuracy of the student's efforts?
In eukaryotes, pyruvate oxidation is carried out in the mitochondrial matrix, not in the cytosol.
Select the arrows that represent enzyme inhibition.
-ATP and NADH are the products of cellular respiration, and when they are abundant, they act to inhibit citrate synthase, the first enzyme of the citric acid cycle. In this way, the cell slows down further production of ATP. - The enzyme isocitrate dehydrogenase is the main control point of the citric acid cycle. When the cell has abundant ATP and NADH (high levels of energy), these molecules inhibit isocitrate dehydrogenase, shutting down the citric acid cycle.
Researchers set up test systems similar to those shown in the tutorial. They used vesicles with and without ATP synthase incorporated into their membranes. The vesicles were placed in various solutions to establish a range of pH conditions as shown in the table. Which test systems would be expected to produce ATP?
2 only
Approximately how many ATP molecules per glucose molecule are produced via glycolysis and cellular respiration?
32
How many reaction steps are involved in the citric acid cycle?
8
A student wants to develop a demonstration to explain the energy changes taking place as electrons are transferred along the respiratory chain. Which everyday objects could he use to accomplish his goal?
A ball rolling down a staircase
Some poisons are compounds that interfere with metabolic pathways. Which poison would interfere with the citric acid cycle but not affect glycolysis?
A compound that inhibits pyruvate dehydrogenase
A student made this diagram as a study guide for learning the steps involved in the aerobic catabolism of glucose. One step could be added to better illustrate these steps. Which step should be added?
A step to show that pyruvate is oxidized to acetyl CoA, the compound that enters the citric acid cycle
Which molecule from glycolysis or the citric acid pathway serves as the building block for lipid synthesis?
Acetyl CoA
Which two solutions can be paired across a membrane to create the greatest potential energy gradient, and in which direction will the flow of protons release this energy?
B to A, 3 to 9
A suspension of yeast supplied with glucose as its source of energy was transferred from an aerobic environment to an anaerobic one. Which result would you predict for the rate of glucose utilization and the rate of ethanol production after the transfer? Assume that the yeast must expend the same amount of energy to survive in both environments.
Both glucose usage and ethanol production would increase.
Which phrase best fills in the missing information in the flowchart?
Chemical energy stored in a proton concentration gradient
Which component of the respiratory chain is a peripheral protein?
Cytochrome c
What is the cellular location of glycolysis in eukaryotes?
Cytosol
This part of the pathway takes place in the inner mitochondrial membrane.
Electrons from NADH + H+ are passed through the respiratory chain, a series of protein complexes in the inner mitochondrial membrane containing electron carriers and enzymes. The carriers gain free energy when they become reduced and release free energy when they are oxidized.
Which compounds link glycolysis and the citric acid cycle to the electron transport chain?
FADH2 and NADH
Electrons are shuttled from glycolysis and the citric acid cycle to the respiratory chain via
FADH2 and NADH.
Which sequence represents a possible path of a carbon atom as it moves through a catabolic series of reactions in a cell?
Fatty acid → acetyl CoA → carbon dioxide
Metabolic pathways are
large sets of interconnected chemical transformational steps, each with a specific enzyme.
In eukaryotes, the organelle containing the enzyme(s) necessary for oxidation of glucose beyond glycolysis is the
mitochondrion.
Compare the amount of glucose consumption needed by an anaerobic fermenting microorganism with that needed by an aerobic organism in order to perform the same functions. The anaerobe would need much (more/less) _______ glucose than the aerobe.
more
The types of chemical reactions involved in the aerobic breakdown of glucose by a cell include
oxidation-reduction reactions and phosphorylations.
The electron transport chain
oxidizes the intermediate electron carriers NADH and FADH2.
The conversion of malate to oxaloacetate in the citric acid cycle takes place with the conversion of NAD+ to NADH. In this reaction, NAD+ is a(n)
oxidizing agent
"Anaerobic conditions" means that there is an absence of
oxygen
Life in its earliest stages was very simple, and bacteria were the dominant life form. However, things changed about 2.3 billion years ago that allowed many new life forms to evolve and multicellularity to emerge. These changes were due to the rise in _______ levels in the atmosphere.
oxygen
Portion of pathway containing the fewest steps
pyruvate oxidation—the portion of the pathway that contains the fewest biochemical steps.
Portion of pathway releasing the smallest amount of energy
pyruvate oxidation—the portion of the pathway that releases the smallest amount of energy.
The end products of glycolysis are
pyruvate, ATP, and NADH
The main difference between lactic acid fermentation and alcoholic fermentation is that lactic acid fermentation
regenerates a three-carbon molecule and alcoholic fermentation does not.
ATP molecules are important in metabolism because ATP can
release chemical energy, which drives endergonic reactions.
Fermentation
results in the formation of either lactic acid or ethanol
The figure illustrates how the F1 subunit _______ as protons move from high to low concentration through the channel formed by the F0 subunit.
rotates
Proteins are built from carbons that come directly from
the citric acid cycle.
Identify the molecule where transported electrons finally end up
water—the final resting place for electrons transported in the electron transport chain. NADH is oxidized by the respiratory chain, and in the process, O2 is reduced to H2O. The electrons from the oxidation of NADH and FADH2 pass from one carrier to the next in the chain, in a process called electron transport
In the complete oxidation of glucose, six CO2 molecules are formed per glucose molecule. The number of CO2 molecules released by glycolysis is _______, by pyruvate oxidation is _______, and by the citric acid cycle is _______.
zero; two; four
Cyanide inhibits the enzyme in the mitochondrial electron transport chain that reduces O2 to water. Suppose you added cyanide to a suspension of muscle cells from a rat. Which statement is accurate with respect to the effects of cyanide on glucose catabolism?
The citric acid cycle would be inhibited, but glycolysis would not and so lactic acid would accumulate
Which statement about the respiratory chain best explains the information presented in the graph?
The components of the respiratory chain are arranged in order so that an electron passing from one to the next undergoes a sequential drop in energy.
When purified cytochrome oxidase is exposed to cyanide, the cyanide binds reversibly and with high affinity to the enzyme's active site. What will be the likely outcome if mitochondria are exposed to high levels of cyanide?
The cyanide will prevent movement of electrons along the electron transport chain.
Which statement best describes steps 1, 2, and 3 of glycolysis (glucose → glucose 6-phosphate → fructose 1,6-bisphosphate)?
These reactions require energy in the form of two ATP per glucose molecule.
Pyruvate oxidation to acetyl CoA is a complex reaction because
it is a multistep chemical reaction involving five different coenzymes and 60 individual proteins
The _______ of the mitochondrion contains the proteins making up the _______ that carry out electron transport.
inner mitochondrial membrane; respiratory chain
Cellular respiration refers to the metabolic process that
involves the oxidation of pyruvate to carbon dioxide.
Under anaerobic conditions, pyruvate
is fermented to lactate or alcohol.
Fermentation is a process that occurs
in muscle tissue when there is an insufficient supply of oxygen.
Fermentation in eukaryotes
In eukaryotes, this energy pathway occurs in the cytoplasm.
Glycolysis in eukaryotes
In eukaryotes, this energy pathway occurs in the cytoplasm.
Citric acid cycle in eukaryotes
In eukaryotes, this energy pathway occurs in the matrix of the mitochondrion.
Pyruvate oxidation in eukaryotes
In eukaryotes, this energy pathway occurs in the matrix of the mitochondrion.
Respiratory chain in eukaryotes
In eukaryotes, this energy pathway occurs on the inner mitochondrial membrane.
This step takes place in the cytoplasm, produces a small amount of energy, and generates no CO2.
In glycolysis, a reduced fuel molecule, glucose, gets partially oxidized and in the process releases some of its energy.
Citric acid cycle in prokaryotes
In prokaryotes, Cytoplasm
Fermentation in prokaryotes
In prokaryotes, this energy pathway occurs in the cytoplasm.
Glycolysis in prokaryotes
In prokaryotes, this energy pathway occurs in the cytoplasm.
Pyruvate oxidation in prokaryotes
In prokaryotes, this energy pathway occurs on the inner face of the plasma membrane.
Respiratory chain in prokaryotes
In prokaryotes, this energy pathway occurs on the inner face of the plasma membrane.
A biochemist discovers several new microorganisms in a sample taken from the bottom of a deep lake in Antarctica. In characterizing one of these organisms, she finds that it cannot survive in an aerobic environment and produces lactic acid as a waste product. What is also likely true about this organism?
It lacks genes for citric acid cycle enzymes.
Which statement about the citric acid cycle is false?
It releases less energy than glycolysis.
Suppose you are constructing a diagram to show the results of experiments with vesicles made to contain both bacteriorhodopsin and ATP synthase. What would the diagram show?
It would show light stimulating bacteriorhodopsin to pump hydrogen ions into the vesicle, which then move back outside the vesicle through ATP synthase, causing it to catalyze ATP formation.
Of the compounds shown, which is the most oxidized, and which is the most reduced?
M is the most oxidized, and P is the most reduced.
Which statement correctly describes this oxidation-reduction reaction?
Malate is oxidized to oxaloacetate, and NAD+ is reduced to NADH.
What is the cellular location of the citric acid cycle?
Mitochondrial matrix
Some of the chemical energy present in pyruvate is harvested during an oxidation-reduction process taking place in the multistep reaction shown in the figure. In which molecule is this harvested chemical energy stored?
NADH
This figure illustrates how two oxidation-reduction reactions are coupled with electrons moving from one compound through another via the coenzyme _______.
NADH
Which statement best describes how key molecules are regenerated to allow continued metabolism in a cell?
NADH and FADH2 can donate their electrons to the electron transport chain and be regenerated to allow the citric acid cycle to continue.
Reagents, such as dinitrophenol, increase the permeability of the mitochondrial inner membrane to protons. The addition of dinitrophenol to a suspension of animal cells should
inhibit mitochondrial ATP synthesis.
Which electron carrier—FADH2 or NADH—contributes more to the proton-motive force across the inner mitochondrial membrane? Click on the correct electron carrier.
NADH donates electrons to the first complex in the respiratory chain. Note that this first complex pumps protons and contributes to the proton gradient (the proton-motive force) that forms across the inner mitochondrial membrane. In contrast, FADH2 bypasses complex I and instead donates electrons to complex II, which does not pump protons. Because the the proton-motive force later drives the production of ATP, more ATP is made from the oxidation of NADH than FADH2 in the respiratory chain.
The outputs of this part of the pathway are carbon dioxide, reduced electron carriers, NADH + H+ and FADH2, and a small amount of ATP.
Overall, for each acetyl group, the citric acid cycle removes two carbons as CO2 and uses four pairs of hydrogen atoms to reduce electron carriers.
If a cell is fed a large supply of fatty acids, which outcome can be expected?
Oxidation of fatty acids through the citric acid cycle will be stimulated until ATP builds up and inhibits citrate synthase, diverting fatty acids into storage molecules such as triglycerides
Malate dehydrogenase is responsible for catalyzing which reaction?
Oxidation of malate to oxaloacetate
Why is oxygen important in the electron transport pathway and ATP synthesis?
Oxygen accepts electrons at the end of the electron transport chain to free the pathway for a new set of electrons.
Which of these arrows represents the allosteric activation of the enzyme phosphofructokinase?
Phosphofructokinase is allosterically activated by ADP or AMP. That is, when the cell needs ATP (energy) and has abundant ADP or AMP available to make ATP, this enzyme is activated.
According to the chemiosmotic mechanism, what is the direct source of the energy used to synthesize ATP from ADP in chloroplasts and in mitochondria?
Proton gradient
Which class of molecules is derived from intermediates in the citric acid cycle?
Pyrimidines
his reaction links glycolysis to the citric acid cycle. Which statement correctly describes the chemical changes depicted in this reaction?
Pyruvate is decarboxylated and oxidized to acetyl CoA, and NAD+ is reduced to NADH.
Which group represents the net outputs of glycolysis?
Pyruvate, 2 NADH, 2 ATP
Which reaction is not an oxidation-reduction reaction?
R — CH = CH — CH3 + H2O → RCH2 — CH (OH) — CH3
How are steps 1-3 of glycolysis different from steps 6-10?
Steps 1-3 catalyze reactions that require ATP, while steps 6-10 catalyze changes that produce NADH and ATP
Which is required for wine production?
Yeast and a source of glucose
Does this figure have any inaccuracies?
Yes, the arrow showing movement of protons through ATP synthase is pointing in the wrong direction; it should be reversed.
The label "X" should be replaced with _______.
carbon dioxide
Portion of pathway that generates the most NADH
citric acid cycle—the portion of the pathway that generates the most NADH.
Like glycolysis, fermentation occurs in theLike glycolysis, fermentation occurs in the
cytosol.
Oxidative phosphorylation has two major components: _______ and _______.
electron transport; chemiosmosis
Metabolic pathways can be controlled through the availability of enzymes and modulation of their catalytic activities. Enzyme availability can be regulated via _______, while enzyme activity is commonly regulated via _______
gene expression; allosteric activation and inhibition
Portion of pathway that consumes ATP
glycolysis—the portion of the pathway that consumes ATP in its initial reactions.
The chemiosmotic mechanism explains
how a proton gradient is coupled to ATP production.
