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In alcohol fermentation, NAD⁺ is regenerated from NADH by
In alcohol fermentation, NAD⁺ is regenerated from NADH by
A) reduction of acetaldehyde to ethanol (ethyl alcohol).
B) oxidation of pyruvate to acetyl CoA.
C) reduction of pyruvate to form lactate.
D) oxidation of ethanol to acetyl CoA.
E) reduction of ethanol to pyruvate.
Answer: A
One function of both alcohol fermentation and lactic acid
fermentation is to
A) reduce NAD⁺ to NADH.
B) reduce FAD⁺ to FADH₂.
C) oxidize NADH to NAD⁺.
D) reduce FADH₂ to FAD⁺.
E) do none of the above.
Answer: C
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
A) must use a molecule other than oxygen to accept
electrons from the electron transport chain.
B) is a normal eukaryotic organism.
C) is photosynthetic.
D) is an anaerobic organism.
E) is a facultative anaerobe.
Answer: E
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?
A) Glycolysis is widespread and is found in the domains
Bacteria, Archaea, and Eukarya.
B) Glycolysis neither uses nor needs O₂.
C) Glycolysis is found in all eukaryotic cells.
D) The enzymes of glycolysis are found in the cytosol
rather than in a membrane-enclosed organelle.
E) Ancient prokaryotic cells, the most primitive of
cells, made extensive use of glycolysis long before oxygen was present in
Earth's atmosphere.
Answer: A
Why is glycolysis considered to be one of the first
metabolic pathways to have evolved?
A) It produces much less ATP than does oxidative
phosphorylation.
B) It does not involve organelles or specialized
structures, does not require oxygen, and is present in most organisms.
C) It is found in prokaryotic cells but not in eukaryotic
cells.
D) It relies on chemiosmosis, which is a metabolic
mechanism present only in the first cells' prokaryotic cells.
E) It requires the presence of membrane-enclosed cell organelles
found only in eukaryotic cells.
Answer: B
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?
A) It is converted to NAD⁺.
B) It produces CO₂ and water.
C) It is taken to the liver and converted back to
pyruvate.
D) It reduces FADH₂ to FAD⁺.
E) It is converted to alcohol.
Answer: C
When skeletal muscle cells are oxygen-deprived, the heart
still pumps. What must the heart muscle cells be able to do?
A) derive sufficient energy from fermentation
B) continue aerobic metabolism when skeletal muscle
cannot
C) transform lactate to pyruvate again
D) remove lactate from the blood
E) remove oxygen from lactate
Answer: B
When skeletal muscle cells undergo anaerobic respiration,
they become fatigued and painful. This is now known to be caused by
A) buildup of pyruvate.
B) buildup of lactate.
C) increase in sodium ions.
D) increase in potassium ions.
E) increase in ethanol.
Answer: B
A mutation in yeast makes it unable to convert pyruvate
to ethanol. How will this mutation affect these yeast cells?
A) The mutant yeast will be unable to grow anaerobically.
B) The mutant yeast will grow anaerobically only when
given glucose.
C) The mutant yeast will be unable to metabolize glucose.
D) The mutant yeast will die because they cannot
regenerate NAD⁺ from NAD.
E) The mutant yeast will metabolize only fatty acids.
Answer: A
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?
A) It was released as CO₂ and H₂O.
B) It was converted to heat and then released.
C) It was converted to ATP, which weighs much less than
fat.
D) It was broken down to amino acids and eliminated from
the body.
E) It was converted to urine and eliminated from the
body.
Answer: A
Phosphofructokinase is an important control enzyme in the
regulation of cellular respiration. Which of the following statements correctly
describes phosphofructokinase activity?
A) It is inhibited by AMP.
B) It is activated by ATP.
C) It is activated by citrate, an intermediate of the
citric acid cycle.
D) It catalyzes the conversion of fructose
1,6-bisphosphate to fructose 6-phosphate, an early step of glycolysis.
E) It is an allosteric enzyme.
Answer: E
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 to
A) inhibit the enzyme and thus slow the rates of
glycolysis and the citric acid cycle.
B) activate the enzyme and thus slow the rates of
glycolysis and the citric acid cycle.
C) inhibit the enzyme and thus increase the rates of
glycolysis and the citric acid cycle.
D) activate the enzyme and increase the rates of
glycolysis and the citric acid cycle.
E) inhibit the enzyme and thus increase the rate of
glycolysis and the concentration of citrate.
Answer: A
Even though plants carry on photosynthesis, plant cells
still use their mitochondria for oxidation of pyruvate. When and where will
this occur?
A) in photosynthetic cells in the light, while
photosynthesis occurs concurrently
B) in nonphotosynthesizing cells only
C) in cells that are storing glucose only
D) in all cells all the time
E) in photosynthesizing cells in the light and in other
tissues in the dark
Answer: D
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?
A) to increase the rate of oxidative phosphorylation from
its few mitochondria
B) to allow the animals to regulate their metabolic rate
when it is especially hot
C) to increase the production of ATP
D) to allow other membranes of the cell to perform
mitochondrial functions
E) to regulate temperature by converting most of the
energy from NADH oxidation to heat
Answer: E
What is the purpose of beta oxidation in respiration?
A) oxidation of glucose
B) oxidation of pyruvate
C) feedback regulation
D) control of ATP accumulation
E) breakdown of fatty acids
Answer: E
Where do the catabolic products of fatty acid breakdown
enter into the citric acid cycle?
A) pyruvate
B) malate or fumarate
C) acetyl CoA
D) α-ketoglutarate
E) succinyl CoA
Answer: C
What carbon sources can yeast cells metabolize to make
ATP from ADP under anaerobic conditions?
A) glucose
B) ethanol
C) pyruvate
D) lactic acid
E) either ethanol or lactic acid
Answer: A
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
A) competitive inhibition.
B) allosteric regulation.
C) the specificity of enzymes for their substrates.
D) an enzyme requiring a cofactor.
E) positive feedback regulation.
Answer: B
During intense exercise, as skeletal muscle cells go into
anaerobiosis, the human body will increase its catabolism of
A) fats only.
B) carbohydrates only.
C) proteins only.
D) fats, carbohydrates, and proteins.
E) fats and proteins only.
Answer: B
Yeast cells that have defective mitochondria incapable of
respiration will be able to grow by catabolizing which of the following carbon
sources for energy?
A) glucose
B) proteins
C) fatty acids
D) glucose, proteins, and fatty acids
E) Such yeast cells will not be capable of catabolizing
any food molecules, and will therefore die.
Answer: A
