MCB Exam 3 HW Questions And
Answers
/.Animals and most microorganisms are classified as chemoorganoheterotrophs. The
prefixes "chemo," "organo," and "hetero" refer to how the organism meets its needs,
respectively, for:
Choose one:
A. carbon, energy, and electrons
B. energy, electrons, and carbon
C. electrons, carbon, and energy
D. carbon, electrons, and energy
E. electrons, energy, and carbon
/.The Gibbs free energy change of a reaction can be calculated using the equation ΔG =
ΔH - TΔS. A biochemical reaction that can provide energy for cellular metabolism would
be one in which:
Choose one:
A. all terms on the right are positive.
B. ΔG was positive.
C. all terms on the right are negative.
D. ΔG was negative.
/.The final step in glycolysis catalyzed by pyruvate kinase couples the hydrolysis of
phosphoenolpyruvate (PEP) to the formation of ATP via substrate-level phosphorylation
of ADP. If the ΔG°' of ATP + H2O → ADP + Pi + H+ is -30.5 kJ/mol and the ΔG°' of the
coupled reaction is -31.4 kJ/mol, what is the ΔG°' of PEP + H2O → pyruvate + Pi?
Choose one:
A. +61.9 kJ/mol
B. More information is needed
C. -0.9 kJ/mol
D. +0.9 kJ/mol
E. -61.9 kJ/mol
/.Sugars are used by many chemoheterotrophs as an important source of carbon and
energy. Indeed, complete oxidation of glucose using oxygen as a terminal electron
acceptor has a free energy change of -2,883.0 kJ/mol. What strategy do cells use to
minimize the amount of that energy that is lost as heat during the catabolism of sugars?
Choose one:
A. The oxidation reaction occurs within insulated organelles.
B. Energy is harvested using a series of smaller oxidations.
,C. The cells employ high-capacity energy carriers (e.g., ΔG°' of hydrolysis ~ -1000
kJ/mol).
D. Oxidations of sugars directly power membrane-bound ATP synthases.
E. Oxidation is directly coupled to biomass synthesis.
/.What are characteristics of respiration, fermentation, and both? - Answer-✅-
Respiration: high ATP yield (mostly from oxidative phosphorylation), most carbon
released as CO2, electrons reduce an external electron acceptor (like oxygen)
- Fermentation: low ATP yield (primarily from glycolysis), electrons from catabolism end
up back on partially oxidized substrate, most carbon remains in organic form
- Both: important for catabolism of sugars, NADH is the major electron carrier, pyruvate
is the major intermediate
/.Ultimately, respiration and fermentation are simply different ways to conclude sugar
catabolism. Following the energy-yielding reactions, respiring cells pass electrons to
oxygen (or other external inorganic oxidant), while fermenting cells dump electrons back
onto a partially oxidized organic molecule (such as pyruvate), which then exits the cell
as a waste product. Either way, the goal is to do which of the following?
Choose one:
A. fully oxidize NADH into CO2 and H2O
B. recycle NADH back to NAD+
C. generate as much NADH as possible (then synthesize more NAD+ if necessary)
D. break down NADH into biosynthetic precursors
E. stimulate de novo production of NAD+
/.Ethanolic fermentation results in which of the following end product(s)?
Choose one or more:
A. acetone
B. carbon dioxide
C. water
D. lactic acid
E. oxygen
F. alcohol
/.The explosive gas, H2, may be produced by commensal E. coli metabolizing sugars
via ___ fermentation. - Answer-✅mixed-acid
/.Certain archaea can also generate a small amount of energy by using the hydrogen
released by E. coli to produce ___ - Answer-✅methane
/.The three tubes in the photograph contain a fermentable carbohydrate (e.g., glucose)
and the pH indicator phenol red. The middle and left tubes were inoculated with
bacteria, and the right tube was left uninoculated as a control. Which of the tubes shows
evidence of fermentation?
, A. left tube
B. middle tube
C. both
D. none
E. impossible to tell without further analysis
/.The pyruvate dehydrogenase complex plays an important role in cellular metabolism
by connecting __ to __.
. - Answer-✅glycolysis; the TCA cycle
/.Because the reduction potential of the CO2/glucose redox pair is more negative than
the Fe3+/Fe2+ redox pair, energy is released as electrons flow
Choose one:
A. from glucose (the donor) to Fe3+ (the acceptor).
B. from glucose (the donor) to Fe2+ (the acceptor).
C. from Fe2+ (the donor) to CO2 (the acceptor).
D. from CO2 (the donor) to Fe3+ (the acceptor).
E. from Fe2+ (the donor) to glucose (the acceptor).
/.What is the minimum number of NADH molecules that must be oxidized for oxygen to
be reduced to water?
Choose one:
A. 1
B. 2
C. 3
D. None; the electrons to reduce water are picked up free from the cytoplasm.
/.The video explains how O2 becomes reduced to H2O during aerobic respiration. In the
example of the bacterial ETS that was given, how many protons were actually lost from
the cytoplasm for every O2 molecule that was consumed?
Choose one:
A. 4
B. 8
C. 28
D. 20
E. 16
/.The ATP synthase can be thought of as a type of molecule motor that is powered by
the flow of ____________ through the subunits and __________ their concentration
gradient.
Choose one:
A. H+ / down
B. e- / down
C. e- / up
D. H+ / up
Answers
/.Animals and most microorganisms are classified as chemoorganoheterotrophs. The
prefixes "chemo," "organo," and "hetero" refer to how the organism meets its needs,
respectively, for:
Choose one:
A. carbon, energy, and electrons
B. energy, electrons, and carbon
C. electrons, carbon, and energy
D. carbon, electrons, and energy
E. electrons, energy, and carbon
/.The Gibbs free energy change of a reaction can be calculated using the equation ΔG =
ΔH - TΔS. A biochemical reaction that can provide energy for cellular metabolism would
be one in which:
Choose one:
A. all terms on the right are positive.
B. ΔG was positive.
C. all terms on the right are negative.
D. ΔG was negative.
/.The final step in glycolysis catalyzed by pyruvate kinase couples the hydrolysis of
phosphoenolpyruvate (PEP) to the formation of ATP via substrate-level phosphorylation
of ADP. If the ΔG°' of ATP + H2O → ADP + Pi + H+ is -30.5 kJ/mol and the ΔG°' of the
coupled reaction is -31.4 kJ/mol, what is the ΔG°' of PEP + H2O → pyruvate + Pi?
Choose one:
A. +61.9 kJ/mol
B. More information is needed
C. -0.9 kJ/mol
D. +0.9 kJ/mol
E. -61.9 kJ/mol
/.Sugars are used by many chemoheterotrophs as an important source of carbon and
energy. Indeed, complete oxidation of glucose using oxygen as a terminal electron
acceptor has a free energy change of -2,883.0 kJ/mol. What strategy do cells use to
minimize the amount of that energy that is lost as heat during the catabolism of sugars?
Choose one:
A. The oxidation reaction occurs within insulated organelles.
B. Energy is harvested using a series of smaller oxidations.
,C. The cells employ high-capacity energy carriers (e.g., ΔG°' of hydrolysis ~ -1000
kJ/mol).
D. Oxidations of sugars directly power membrane-bound ATP synthases.
E. Oxidation is directly coupled to biomass synthesis.
/.What are characteristics of respiration, fermentation, and both? - Answer-✅-
Respiration: high ATP yield (mostly from oxidative phosphorylation), most carbon
released as CO2, electrons reduce an external electron acceptor (like oxygen)
- Fermentation: low ATP yield (primarily from glycolysis), electrons from catabolism end
up back on partially oxidized substrate, most carbon remains in organic form
- Both: important for catabolism of sugars, NADH is the major electron carrier, pyruvate
is the major intermediate
/.Ultimately, respiration and fermentation are simply different ways to conclude sugar
catabolism. Following the energy-yielding reactions, respiring cells pass electrons to
oxygen (or other external inorganic oxidant), while fermenting cells dump electrons back
onto a partially oxidized organic molecule (such as pyruvate), which then exits the cell
as a waste product. Either way, the goal is to do which of the following?
Choose one:
A. fully oxidize NADH into CO2 and H2O
B. recycle NADH back to NAD+
C. generate as much NADH as possible (then synthesize more NAD+ if necessary)
D. break down NADH into biosynthetic precursors
E. stimulate de novo production of NAD+
/.Ethanolic fermentation results in which of the following end product(s)?
Choose one or more:
A. acetone
B. carbon dioxide
C. water
D. lactic acid
E. oxygen
F. alcohol
/.The explosive gas, H2, may be produced by commensal E. coli metabolizing sugars
via ___ fermentation. - Answer-✅mixed-acid
/.Certain archaea can also generate a small amount of energy by using the hydrogen
released by E. coli to produce ___ - Answer-✅methane
/.The three tubes in the photograph contain a fermentable carbohydrate (e.g., glucose)
and the pH indicator phenol red. The middle and left tubes were inoculated with
bacteria, and the right tube was left uninoculated as a control. Which of the tubes shows
evidence of fermentation?
, A. left tube
B. middle tube
C. both
D. none
E. impossible to tell without further analysis
/.The pyruvate dehydrogenase complex plays an important role in cellular metabolism
by connecting __ to __.
. - Answer-✅glycolysis; the TCA cycle
/.Because the reduction potential of the CO2/glucose redox pair is more negative than
the Fe3+/Fe2+ redox pair, energy is released as electrons flow
Choose one:
A. from glucose (the donor) to Fe3+ (the acceptor).
B. from glucose (the donor) to Fe2+ (the acceptor).
C. from Fe2+ (the donor) to CO2 (the acceptor).
D. from CO2 (the donor) to Fe3+ (the acceptor).
E. from Fe2+ (the donor) to glucose (the acceptor).
/.What is the minimum number of NADH molecules that must be oxidized for oxygen to
be reduced to water?
Choose one:
A. 1
B. 2
C. 3
D. None; the electrons to reduce water are picked up free from the cytoplasm.
/.The video explains how O2 becomes reduced to H2O during aerobic respiration. In the
example of the bacterial ETS that was given, how many protons were actually lost from
the cytoplasm for every O2 molecule that was consumed?
Choose one:
A. 4
B. 8
C. 28
D. 20
E. 16
/.The ATP synthase can be thought of as a type of molecule motor that is powered by
the flow of ____________ through the subunits and __________ their concentration
gradient.
Choose one:
A. H+ / down
B. e- / down
C. e- / up
D. H+ / up
