Deck 14: Electron Flow in Organotrophy, Lithotrophy, and Phototrophy

Question 1

Although embedded in the membrane as an ETS component, the enzyme __________ does not pump protons.

A) pyruvate dehydrogenase
B) 2-oxoglutarate dehydrogenase
C) succinate dehydrogenase
D) malate dehydrogenase
E) glyceraldehyde dehydrogenase

Answer 1

C

Question 2

In cytochromes, the heme group plays a key role in acquiring and transferring electrons with a(n) __________ transition.

A) Mg0/Mg2+
B) S0/S2-
C) Cu+/Cu2+
D) Fe3+/Fe2+
E) Mn0/MN₂+

Answer 2

D

Question 3

The following are cellular processes that can be directly powered by the proton motive force (Δp), EXCEPT

A) ATP biosynthesis from ADP and Pi.
B) flagellar rotation.
C) nutrient uptake.
D) drug efflux in some pathogens.
E) protein biosynthesis.

Answer 3

E

Question 4

The diagram below shows the structure of the universal FₒF₁ synthase. Which of the following FALSELY labels the figure?

A) i) Fo subunit
B) ii) F1 subunit
C) iii) catalytic subunit
D) iv) subunit a
E) v) subunit b

Question 5

Enzymes transferring electrons at the start of the ETS are referred to as __________, whereas enzymes transferring electrons to the terminal electron acceptor are designated as __________.

A) dehydrogenases; oxidases
B) oxidases; dehydrogenases
C) sulfatases; nitrogenases
D) permeases; proton pumps
E) lyases; hydrolases

Question 6

Which of the following is FALSE regarding the ETS in Escherichia coli?

A) NDH-1 is the main initial substrate oxydoreductase; NDH-2 is an alternative NADH dehydrogenase.
B) It pumps 10-12 protons per NADH.
C) It pumps 2-8 protons per NADH.
D) The main terminal oxidase is the cytochrome bo quinol oxidase, which contains heme b, heme O3, and Cu.
E) An alternative cytochrome bd quinol oxidase has a higher affinity for oxygen than other terminal oxidases and allows E. coli growth in low-O₂ habitats.

Question 7

Which of the following is FALSE regarding the electron transfer system in mitochondria?

A) The subunits of cytochrome c oxidoreductase (complex IV) are associated to eukaryotic proteins.
B) Oxidation of NADH + H+ contributes to the formation of a larger Dp.
C) The initial oxidoreductase, the NADH dehydrogenase (complex I), pumps more protons than the NDH-1 in Escherichia coli.
D) The succinate dehydrogenase (complex II) contributes to Dp by pumping protons onto the intermembrane space.
E) The ETS of some bacteria, such as Paracoccus denitrificans, are organized in a manner similar to that of mitochondria.

Question 8

The chemiosmotic theory states that the proton potential is composed of

A) [ATP] and [ADP]+[Pi].
B) a pH gradient and [Na+] gradient.
C) pH and pNa+.
D) DpH and DY
E) a pH gradient and a [Ca2+] wave.

Question 9

How are drug efflux pumps spread among virulent bacterial strains?

A) They are spread through generalized transduction.
B) Their genes are contained in plasmids that are transmitted among bacterial cells.
C) They are spread through conjugation between two virulent strains.
D) They are spread through transformation with Hfr plasmids.
E) DNA is released from bacterial cells previously infected with bacteriophages.

Question 10

Protons can have different fates in bacterial ETS. Which of the following processes does NOT affect the proton motive force (Δp)?

A) Protons are pumped across the membrane (H+) by oxidoreductase complexes.
B) Protons are consumed from the cytoplasm by the quinone/quinol pool.
C) Protons are released outside the membrane from the quinone/quinol pool.
D) Protons are consumed by combining with terminal electron acceptors such as O₂.
E) Protons combining with O₂, used as a terminal acceptor, compensate protons released by catabolic pathways.

Question 11

While testing the chemiosmotic theory across the domains of life, researchers prepared "inside-out" vesicles from bacterial plasma membranes, mitochondrial internal membranes, and chloroplast thylakoids. An inside-out vesicle is a

A) vesicle in which the F1 subunit of the proton-ATPase faces outward.
B) membrane in which the hydrophobic tails of the phospholipids face outward.
C) cell that has been enzymatically stripped of its cell wall.
D) preparation of outer membranes in Gram-negative bacteria, chloroplast envelopes, and mitochondria outer membranes.
E) preparation from bacterial cytoplasm, chloroplast stroma, and mitochondrial matrix.

Question 12

Which of the following is NOT a redox pair?

A) fumarate/succinate
B) NADH + H+/NAD
C) H₂S/H₂O
D) quinone/quinol (Q/QH₂)
E) FAD/FADH₂

Question 13

The following groups or molecules are components of electron transport systems, EXCEPT

A) heme
B) [2Fe-2S] and [4Fe-4S] iron-sulfur clusters.
C) quinones.
D) flavin mononucleotide.
E) acetyl-S-CoA.

Question 14

In a redox reaction, the reduction potential E depends on the ratio of product concentrations ([C] and [D]) to reactant concentrations ([A]  and  [B]), as per equation E  =  E°'  -  60  (mV/n)  log  [C][D]/[A][B]. What would be the effect of increasing the ratio of products to reactants by a factor of 10?

A) No effect: E°' assumes 1-M concentrations of reactants and products.
B) A change of -60 mV will not modify the estimate of E.
C) The value of E will decrease by 60 mV, decreasing energy yield.
D) The value of E will increase by 60 mV, increasing energy yield.
E) The E°' term is unaffected by changes in concentrations of products or reactants.

Question 15

Which of the following substrates is an electron donor in organotrophy?

A) Fe2+
B) succinate
C) NO₂
D) H₂
E) H₂O

Question 16

Reduction potential is defined as

A) the tendency for a compound to release H+ in solution.
B) the tendency for a compound to release OH- in solution.
C) the tendency of a compound to accept electrons.
D) the tendency of a compound to donate electrons.
E) a synonym for chemical valence.

Question 17

What is lithotrophy?

A) breakdown of molecules using light energy
B) oxidation of organic electron donors to CO₂ and H₂O
C) photolysis of H₂S or H₂O coupled to CO₂ fixation
D) oxidation of inorganic electron donors such as Fe2+ using O₂ or anaerobic electronic acceptors
E) physical breakdown of food particles to facilitate ingestion

Question 18

The molecule shown below, __________, is a cofactor for electron transport.

A) a cytochrome
B) ubiquinone
C) flavin mononucleotide
D) nicotine amide dinucleotide
E) heme b

Question 19

Which of the following is NOT true of 2,4-dinitrophenol (DNP)?

A) It is an uncoupler.
B) It can be used to measure ΔpH.
C) Unprotonated DNP can cross the membrane.
D) Protonated DNP can cross the membrane.
E) It dissipates the proton motive force.

Question 20

Electron transport systems are embedded in all of the following membrane systems EXCEPT

A) the mitochondrial inner membrane.
B) thylakoids.
C) the inner membrane of Gram-negative bacteria.
D) the eukaryotic plasma membrane.
E) the archaeal plasma membrane.

Question 21

Ferroplasma acidarmanus produces large amounts of sulfuric acid through

A) oxidation of Cu+ with Cu(NO3)2.
B) oxidation of FeS2 with Fe3+ and H₂O.
C) oxidation of Fe3O₂ with Fe2+.
D) oxidation of H₂S with H₂O.
E) reduction of SO with H₂.

Question 22

Which of the following is FALSE with respect to the use of sulfate by marine archaeal and bacterial groups?

A) Oxidized sulfur-containing molecules have redox potentials lower than those of the nitrogen series.
B) Oxidized sulfur molecules such as sulfate and sulfite serve as electron acceptors.
C) Sulfate and sulfite can receive electrons from hydrocarbons.
D) Sulfate-reducing archaea and bacteria are widespread in the ocean.
E) Sulfate is more abundant than chloride in the ocean.

Question 23

The Fₒ portion of Escherichia coli ATP synthase that rotates while translocating protons is

A) the g drive shaft.
B) subunits a and
C) a ring of 8 to 15 c subunits.
D) an ab - subunit.
E) the catalytic active site.

Question 24

Which of the following is NOT a terminal electron acceptor in anaerobic respirations?

A) nitrate
B) nitrite
C) hydrogen sulfide
D) carbon dioxide
E) sulfate

Question 25

The reduction of U⁶⁺ to U⁴⁺ by Geobacter metallireducens is an example of

A) assimilatory metal reduction.
B) fermentation.
C) dissimilatory metal reduction.
D) organotrophy.
E) lithotrophy.

Question 26

In marine sediments, CO₂ is reduced to CH₄ by

A) bacteria containing proteorhodopsin.
B) oxygenic cyanobacteria.
C) methanotrophic archaea.
D) methanogenic archaea.
E) nonpurple sulfur bacteria.

Question 27

Sulfolobus species produce __________; as a result, their immediate environment has a pH __________.

A) H₂SO₄; as low as 2
B) H3PO4; as low as 3
C) HCl; of 1
D) CH3COOH; of 4
E) HCOOH; of 3

Question 28

Which of the following is NOT correct about the process of methanogenesis?

A) CO₂ and H₂O are weak electron acceptors, whereas CH4 and H₂ are strong electron donors.
B) CH4 synthesis from CO₂ releases energy for growth.
C) CH4 and water can be formed from CO₂ and 4H₂ from a hydrogen donor.
D) Oxygen atoms in CO₂ are reduced one at a time.
E) Oxygen atoms in CO₂ are reduced to water at the same time.

Question 29

In anaerobic soils, some yeasts and filamentous fungi can reduce nitrate to nitrite and nitrite to

A) ammonia (NH3).
B) nitric oxide (NO).
C) urea.
D) nitrogen gas (N₂).
E) ammonium hydroxide (NH4OH).

Question 30

Which of the following is FALSE regarding dehalorespiration?

A) It is a type of hydrogenotrophy.
B) Cl- can be removed from toxic compounds by dehalorespiration.
C) Nitrogen (N₂) is a by-product of dehalorespiration.
D) Halogenated organic molecules serve as electron acceptors for H₂.
E) Hydrogenotrophs can be used in bioremediation.

Question 31

Which of the following reactions is possible by reverse electron flow?

A) reduction of Fe3+ to Fe2+
B) NADP+ reduction to NADPH
C) protein biosynthesis
D) reduction of oxygen by Fe2+ to form H₂O and Fe3+
E) anammox

Question 32

The anammox reaction consists of __________ and, as a consequence, __________.

A) reduction of sulfate by ammonia; sulfur and nitrogen are incorporated into amino acids
B) reduction of ammonium to form nitrite; plants can absorb nitrite
C) anaerobic ammonium oxidation by nitrite; large amounts of N₂ are released into the atmosphere
D) reduction of ammonium by water; ammonium becomes ammonia
E) reduction of N₂ to ammonium; nitrogen atoms are incorporated into amino acids

Question 33

Which species can be utilized in biomining because it oxidizes copper and iron sulfides?

A) Geobacter metallireducens
B) Sulfurospirillum barnesii
C) Haloferax volcanii
D) Acidithiobacillus ferrooxidans
E) Bacillus subtilis

Question 34

In purple bacteria, bacteriochlorophylls are supplemented by accessory pigments called

A) antenna complexes.
B) bacteriorhodopsin.
C) carotenoids.
D) chlorophylls.
E) thylakoids.

Question 35

What is the chromophore group in bacteriorhodopsin?

A) tocopherol
B) b-carotene
C) folic acid
D) retinal
E) chlorophyll

Question 36

Extreme halophilic archaea exclusively utilize which kind of ion gradient?

A) H+
B) Na+
C) Ca2+
D) K+
E) Mg2+

Question 37

Nitrifiers are bacteria

A) that generate nitrites or nitrates.
B) that convert N₂ to NH3.
C) capable of oxidizing NH3 using NO.
D) capable of living in symbiosis in the roots of some plants.
E) capable of using NH3 as an electron donor.

Question 38

The figure below shows anaerobic corrosion of a piece of steel accelerated by the action of anaerobic microorganisms. What should be on label 2?

A) Elemental sulfur and iron directly react to produce FeS.
B) Iron reduces
C) Acid rain is produced:
D) Acid rain is produced:
E) Acid rain is produced:

Question 39

Neisseria species use dissimilatory reduction of nitrate to ammonium. How can this reaction be used to distinguish Neisseria gonorrhoeae from other related species?

A) N. gonorrhoeae will test negative for terminal NO reductase.
B) N. gonorrhoeae will test positive for terminal NO reductase.
C) All Neisseria species test negative for terminal NO reductase.
D) All Neisseria species test positive for terminal NO reductase.
E) None of the enzymes involved in dissimilatory reduction of nitrate are known from species of Neisseria.

Question 40

In dehalorespiration of chlorinated pollutants, the chlorine is removed and replaced by

A) hydrogen.
B) oxygen.
C) nitrogen.
D) sulfur.
E) ammonia.

Question 41

While testing the chemiosmotic theory, rescarchers prepared vesicles from bacterial
cells, mitochondrial internal membranes, and chloroplast thylakoids. In an inside-out vesicle, the
subunit of the proton-ATPase faces outward. Using the figure below, briefly discuss how the
use of inside-out vesicles helped to study the relative contributions of the proton gradient
and the membrane potential to

Question 42

How does Shewanella oneidensis donate electrons to oxidized minerals in marine sediments?

Question 43

Use the figure below to describe Peter Mitchell's chemiosmotic model for coupling the electron transfer system with ATP synthesis.

Question 44

The organism __________ is also known as "the bacterium that eats everything." It conducts photoheterotrophy and fixes nitrogen as ammonium while generating H₂. It also produces ATP via cyclic photophosphorylation in photosystem II.

A) Pseudochrobactrum saccharolyticum
B) Nitrobacter winogradskyi
C) Bradyrhizobium japonicum
D) Rhodopseudomonas palustris
E) Brucella pinnipedialis

Question 45

Is the synthesis of ATP by the F₁Fₒ ATPase reversible? If so, are there any examples?

Question 46

Which of the following definitions is FALSE?

A) Photosynthesis is hotolysis followed by CO₂ fixation and biosynthesis.
B) Photolysis is light absorption coupled to splitting of a molecule.
C) Photophosphorylation is the reaction ADP + Pi ATP catalyzed by photons.
D) Photoexcitation is light absorption causing an electron to transfer to a higher energy state.
E) Photoionization is light absorption that causes electron separation.

Question 47

Why and how is it that mitochondria have only a single electron transport system (ETS), unlike many bacteria?

Question 48

Electron donors for anaerobic photosystem I in green sulfur bacteria and chloroflexi include the following, EXCEPT

A) H₂S.
B) HS.-
C) H₂.
D) H₂O.
E) Fe2+.

Question 49

In the Rhodospirillum rubrum photosystem II, bacteriochloropyll P870 can absorb weak infrared wavelengths in the __________ range.

A) 600-650
B) 650-700
C) 700-750
D) 750-800
E) 800-1,100

Question 50

In photosystem II of purple bacteria, electrons flow through cytochrome bc, coupled to pumping of protons and the proton potential drives synthesis of ATP. The cytochrome bc complex transfers the electrons back to bacteriochlorophyll P870. This type of ATP synthesis is called

A) reverse electron flow.
B) membrane potential.
C) noncyclic photophosphorylation.
D) cyclic photophosphorylation.
E) proton motive force.

Question 51

What factors may affect Δp in metabolically active bacterial cells?

Question 52

In oxygenic photosynthesis, __________ is the electron donor, whereas in anaerobic photosynthesis it can be succinate or __________.

A) H₂S; S0
B) O₂; H₂
C) O₂; H₂O
D) H₂O; H₂S
E) H₂S; SO

Question 53

The direction of the proton current in the chloroplast F₁Fₒ ATP synthase during ATP synthesis is from

A) stroma to cytoplasm.
B) cytoplasm to stroma.
C) lumen to stroma.
D) stroma to lumen.
E) one thylakoid to another through their lumen.

Question 54

Phototrophy is

A) photolysis.
B) use of photoexcited electrons to power cell growth.
C) chlorophyll photoexcitation.
D) photoionization.
E) a charge-separating photopigment.

Question 55

Some respiratory bacteria, such as the nitrate oxidizer, nitospira, pack their ETS within intracytoplasmic pockets called

A) insoluable particles.
B) mitochondrial inner membrane.
C) inner membrane space.
D) cristae.
E) lamellae.

Question 56

The figure below represents absorbance spectra of a cytochrome from the membrane of the archaeon Haloferax volcanii. The spectrum from the reduced form is represented by a continuous line and the oxidized form by a dashed line. Describe the differences between the spectra and which wavelength you would use to study the redox reactions of this cytochrome.

Question 57

The chlorophyll chromophore consists of a heteroaromatic ring complexed to a __________ ion.

A) calcium
B) chloride
C) magnesium
D) manganese
E) potassium

Question 58

Use the figure below to describe how an uncoupler functions. Can an uncoupler be used as an antibiotic to treat bacterial infections?

Question 59

Cyanobacteria have __________-based photosynthesis and are the only __________-producing bacteria.

A) H₂S; S0
B) Mg2+; NO
C) H₂O; O₂
D) succinate; O₂
E) fumarate; O₂

Question 60

Which organism can respire with uranium and remediate uranium-contaminated water?

A) R. palustris
B) Shewanella sp
C) G. metallireducens
D) Salmonella sp
E) Brucella sp

Question 61

Use the figure below to describe Salmonella enterica respiration on tetrathionate. What is the advantage of using this anaerobic respiratory mechanism?

Question 62

What is dissimilatory metal reduction? How is it different from assimilatory metal reduction? Is there application of the dissimilatory metal reduction phenomenon?

Question 63

Describe the role of the thylakoids in purple bacteria and cyanobacteria. Why is it that pumping protons into the lumen is essentially equivalent to pumping protons out of the cell?

Question 64

What are methanotrophs? What is their role in the global carbon cycle?

Question 65

Use the figure below to describe how Acidithiobacillus ferrooxidans can utilize iron as an electron donor for ATP production. Discuss how other microbes benefit from or contribute to the process.

Question 66

The F₁Fₒ ATP synthase is a remarkably complex enzyme, its subunit structure highly conserved across life domains. Is it possible to use this enzyme as an antibiotic target?

Question 67

What is photoheterotrophy? Give examples of photoheterotrophic organisms.

Question 68

Explain what kind of reaction bacteriorhodopsin performs and what it accomplishes for the cell. What is the name of the bacteriorhodopsin homologs, in what type of organisms were they identified, and what led to their discovery?

Question 69

How does photosystem I allow Chlorobium and other green sulfur bacteria to live near deep-sea vents?

Question 70

How does bacteriorhodopsin couple photoexcitation with proton pumping? How is ATP synthesized in bacteriorhodopsin-containing organisms?