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80 terms

Chap:9 solutions

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What is the term for metabolic pathways that release stored energy by breaking down complex molecules?
catabolic pathways
The molecule that functions as the reducing agent (electron donor) in a redox or oxidation-reduction reaction
loses electrons and loses potential energy
When electrons move closer to a more electronegative atom, what happens?
The more electronegative reduced, and energy is released
) Why does the oxidation of organic compounds by molecular oxygen to produce CO2 and water release free energy?
Electrons are being moved from atoms that have a lower affinity for electrons (such as C) to atoms with a higher affinity for electrons (such as O
Which of the following statements describes the results of this reaction?
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy
C6H12O6 is oxidized and O2 is reduced.
) When a glucose molecule loses a hydrogen atom as the result of an oxidation-reduction reaction, the molecule becomes
oxidized
When a molecule of NAD+ (nicotinamide adenine dinucleotide) gains a hydrogen atom (not a proton), the molecule becomes
reduced
Which of the following statements describes NAD+?
NAD+ is reduced to NADH during glycolysis, pyruvate oxidation, and the citric acid cycle
Where does glycolysis take place in eukaryotic cells
in the cytosol
The ATP made during glycolysis is generated by
substrate-level phosphorylation
The oxygen consumed during cellular respiration is involved directly in which process or event?
accepting electrons at the end of the electron transport chain
Which process in eukaryotic cells will proceed normally whether oxygen (O2) is present or absent
glycolysis
An electron loses potential energy when it
shifts to a more electronegative atom.
Why are carbohydrates and fats considered high energy foods
They have a lot of electrons associated with hydrogen.
Substrate-level phosphorylation accounts for approximately what percentage of the ATP formed by the reactions of glycolysis?
100%
During glycolysis, when each molecule of glucose is catabolized to two molecules of pyruvate, most of the potential energy contained in glucose is
retained in the pyruvate
In addition to ATP, what are the end products of glycolysis?
NADH and pyruvate
The free energy for the oxidation of glucose to CO2 and water is -686 kcal/mol and the free energy for the reduction of NAD+ to NADH is +53 kcal/mol. Why are only two molecules of NADH formed during glycolysis when it appears that as many as a dozen could be formed?
Most of the free energy available from the oxidation of glucose remains in pyruvate, one of the products of glycolysis
Starting with one molecule of glucose, the energy-containing products of glycolysis are
2 NAD+, 2 pyruvate, and 2 ATP.
In glycolysis, for each molecule of glucose oxidized to pyruvate
two molecules of ATP are used and four molecules of ATP are produced
A molecule that is phosphorylated
has an increased chemical potential energy; it is primed to do cellular work
Which kind of metabolic poison would most directly interfere with glycolysis
an agent that closely mimics the structure of glucose but is not metabolized
Why is glycolysis described as having an investment phase and a payoff phase
It uses stored ATP and then forms a net increase in ATP.
The transport of pyruvate into mitochondria depends on the proton-motive force across the inner mitochondrial membrane. How does pyruvate enter the mitochondrion
active transport
Which of the following intermediary metabolites enters the citric acid cycle and is formed, in part, by the removal of a carbon (CO2) from one molecule of pyruvate?
Acetyl CoA
During cellular respiration, acetyl CoA accumulates in which location
mitochondrial matrix
How many carbon atoms are fed into the citric acid cycle as a result of the oxidation of one molecule of pyruvate
two
Carbon dioxide (CO2) is released during which of the following stages of cellular respiration
oxidation of pyruvate to acetyl CoA and the citric acid cycle
) A young animal has never had much energy. He is brought to a veterinarian for help and is sent to the animal hospital for some tests. There they discover his mitochondria can use only fatty acids and amino acids for respiration, and his cells produce more lactate than normal. Of the following, which is the best explanation of his condition?
His mitochondria lack the transport protein that moves pyruvate across the outer mitochondrial membrane.
During aerobic respiration, electrons travel downhill in which sequence
food → NADH → electron transport chain → oxygen
What fraction of the carbon dioxide exhaled by animals is generated by the reactions of the citric acid cycle, if glucose is the sole energy source?
2/3
Where are the proteins of the electron transport chain located
mitochondrial inner membrane
In cellular respiration, the energy for most ATP synthesis is supplied by
a proton gradient across a membrane.
During aerobic respiration, which of the following directly donates electrons to the electron transport chain at the lowest energy level?
FADH2
The primary role of oxygen in cellular respiration is to
act as an acceptor for electrons and hydrogen, forming water.
Inside an active mitochondrion, most electrons follow which pathway
citric acid cycle → NADH → electron transport chain → oxygen
During aerobic respiration, H2O is formed. Where does the oxygen atom for the formation of the water come from
) molecular oxygen (O2)
) In chemiosmotic phosphorylation, what is the most direct source of energy that is used to convert ADP + Pi to ATP?
energy released from movement of protons through ATP synthase, down the electrochemical gradient
Energy released by the electron transport chain is used to pump H+ into which location in eukaryotic cells?
D) mitochondrial intermembrane space
The direct energy source that drives ATP synthesis during respiratory oxidative phosphorylation in eukaryotic cells is
the proton-motive force across the inner mitochondrial membrane
When hydrogen ions are pumped from the mitochondrial matrix across the inner membrane and into the intermembrane space, the result is the
lowering of pH in the mitochondrial matrix
Where is ATP synthase located in the mitochondrion
inner membrane
It is possible to prepare vesicles from portions of the inner mitochondrial membrane. Which one of the following processes could still be carried on by this isolated inner membrane
oxidative phosphorylation
How many oxygen molecules (O2) are required each time a molecule of glucose (C6H12O6) is completely oxidized to carbon dioxide and water via aerobic respiration
6
Which of the following produces the most ATP when glucose (C6H12O6) is completely oxidized to carbon dioxide (CO2) and water?
oxidative phosphorylation (chemiosmosis)
Approximately how many molecules of ATP are produced from the complete oxidation of two molecules of glucose (C6H12O6) in aerobic cellular respiration?
60-64
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.
Chemiosmotic ATP synthesis (oxidative phosphorylation) occurs in
all respiring cells, both prokaryotic and eukaryotic, using either oxygen or other electron acceptors
If a cell is able to synthesize 30 ATP molecules for each molecule of glucose completely oxidized by carbon dioxide and water, how many ATP molecules can the cell synthesize for each molecule of pyruvate oxidized to carbon dioxide and water
12
What is proton-motive force?
the force exerted on a proton by a transmembrane proton concentration gradient
In liver cells, the inner mitochondrial membranes are about five times the area of the outer mitochondrial membranes. What purpose must this serve
increasing surface area for oxidative phosphorylation.
) Brown fat cells produce a protein called thermogenin in their mitochondrial inner membrane. Thermogenin is a channel for facilitated transport of protons across the membrane. What will occur in the brown fat cells when they produce thermogenin?
ATP synthesis will decrease, and heat generation will increase
In a mitochondrion, if the matrix ATP concentration is high, and the intermembrane space proton concentration is too low to generate sufficient proton-motive force, then
ATP synthase will hydrolyze ATP and pump protons into the intermembrane space.
In prokaryotes, the respiratory electron transport chain is located
in the plasma membrane
Which catabolic processes may have been used by cells on ancient Earth before free oxygen became available?
glycolysis, pyruvate oxidation, the citric acid cycle, and oxidative phosphorylation, using an electron acceptor other than oxygen
Which of the following normally occurs regardless of whether or not oxygen (O2) is present
glycolysis
Which of the following occurs in the cytosol of a eukaryotic cell
glycolysis and fermentation
Which metabolic pathway is common to both cellular respiration and fermentation
glycolysis
The ATP made during fermentation is generated by which of the following?
substrate-level phosphorylation
In the absence of oxygen, yeast cells can obtain energy by fermentation, resulting in the production of
ATP, CO2, and ethanol (ethyl alcohol).
) In alcohol fermentation, NAD+ is regenerated from NADH by
reduction of acetaldehyde to ethanol (ethyl alcohol
One function of both alcohol fermentation and lactic acid fermentation is to
oxidize NADH to NAD+
An organism is discovered that thrives both in the presence and absence of oxygen in the air. Curiously, the consumption of sugar increases as oxygen is removed from the organism's environment, even though the organism does not gain much weight. This organism is
falcutative anerobe
Which statement best supports the hypothesis that glycolysis is an ancient metabolic pathway that originated before the last universal common ancestor of life on Earth?
Glycolysis is widespread and is found in the domains Bacteria, Archaea, and Eukarya
Why is glycolysis considered to be one of the first metabolic pathways to have evolved?
It does not involve organelles or specialized structures, does not require oxygen, and is present in most organisms.
) When an individual is exercising heavily and when the muscle becomes oxygen-deprived, muscle cells convert pyruvate to lactate. What happens to the lactate in skeletal muscle cells
It is taken to the liver and converted back to pyruvate.
) When skeletal muscle cells are oxygen-deprived, the heart still pumps. What must the heart muscle cells be able to do?
continue aerobic metabolism when skeletal muscle cannot
When skeletal muscle cells undergo anaerobic respiration, they become fatigued and painful. This is now known to be caused
build up of lactate
A mutation in yeast makes it unable to convert pyruvate to ethanol. How will this mutation affect these yeast cells?
The mutant yeast will be unable to grow anaerobically
You have a friend who lost 7 kg (about 15 pounds) of fat on a regimen of strict diet and exercise. How did the fat leave her body?
It was released as CO2 and H2O.
Phosphofructokinase is an important control enzyme in the regulation of cellular respiration. Which of the following statements correctly describes phosphofructokinase activity?
It is an allosteric enzyme
Phosphofructokinase is an allosteric enzyme that catalyzes the conversion of fructose 6-phosphate to fructose 1,6-bisphosphate, an early step of glycolysis. In the presence of oxygen, an increase in the amount of ATP in a cell would be expected
) inhibit the enzyme and thus slow the rates of glycolysis and the citric acid cycle
Even though plants carry on photosynthesis, plant cells still use their mitochondria for oxidation of pyruvate. When and where will this occur?
) in all cells all the time
In vertebrate animals, brown fat tissue's color is due to abundant blood vessels and capillaries. White fat tissue, on the other hand, is specialized for fat storage and contains relatively few blood vessels or capillaries. Brown fat cells have a specialized protein that dissipates the proton-motive force across the mitochondrial membranes. Which of the following might be the function of the brown fat tissue
to regulate temperature by converting most of the energy from NADH oxidation to heat
What is the purpose of beta oxidation in respiration
breakdown of fatty acids
Where do the catabolic products of fatty acid breakdown enter into the citric acid cycle
acetyl coA
What carbon sources can yeast cells metabolize to make ATP from ADP under anaerobic conditions?
glucose
High levels of citric acid inhibit the enzyme phosphofructokinase, a key enzyme in glycolysis. Citric acid binds to the enzyme at a different location from the active site. This is an example of
allosteric regulation.
During intense exercise, as skeletal muscle cells go into anaerobiosis, the human body will increase its catabolism of
carb only
Yeast cells that have defective mitochondria incapable of respiration will be able to grow by catabolizing which of the following carbon sources for energy?
glucose