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

Question 1

Which of the following groups or molecules are components of electron transport systems?

A) heme and flavin mononucleotide
B) [2Fe-2S] and [4Fe-4S] iron-sulfur clusters
C) quinones and quinols
D) all of the above
E) none of the above

Answer 1

D

Question 2

A special kind of __________ flows among membrane-embedded proteins and cofactors, generating a(n) __________.

A) proton current; ion gradient
B) electrical current; pH gradient
C) electrical current; proton current
D) all of the above
E) none of the above

Answer 2

B

Question 3

Which of the following is NOT a redox pair?

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

Answer 3

C

Question 4

Extreme halophilic archaea exclusively utilize which kind of ion gradient?

A) proton
B) sodium ion
C) potassium ion
D) calcium ion
E) magnesium ion

Question 5

Electron transport systems are embedded in what membrane system, among others?

A) mitochondrial inner membrane
B) thylakoids
C) the inner membrane of Gram-negative bacteria
D) all of the above
E) none of the above

Question 6

Some pathogenic bacteria use __________ to expel antibiotics from the cell.

A) proton-driven efflux pumps
B) sugar or amino acid inward carriers
C) heme cofactors
D) all of the above
E) none of the above

Question 7

In Gram-negative bacteria, the ETS is embedded in the:

A) inner membrane
B) cell wall
C) periplasm
D) outer membrane
E) none of the above

Question 8

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

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

Question 9

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) $\Delta$ pH and $\Delta$$\varPsi$
E) none of the above

Question 10

How are drug efflux pumps spread among virulent bacterial strains?

A) generalized transduction
B) their genes are contained in plasmids that are transmitted among bacterial cells
C) conjugation between virulent and nonvirulent strains
D) transformation with Hfr plasmids
E) DNA is released from bacterial cells previously infected with bacteriophages

Question 11

In some electron carriers, small energy transitions may involve cofactors such as:

A) dehydrogenase and oxidases
B) heteroatom and peptide bonds
C) metal ions, conjugated bonds, and heteroaromatic rings
D) none of the above
E) all of the above

Question 12

Which of the following enzymes is embedded in the membrane as an ETS component?

A) pyruvate dehydrogenase
B) 2-oxoglutarate dehydrogenase
C) succinate dehydrogenase
D) aconitase
E) none of the above

Question 13

The relationship between the electrical and chemical components of $\Delta$ p is given by the equation:

A) $\Delta$ p = $\Delta$$\varPsi$ - (2.3RT/F) $\Delta$ pH
B) $\Delta$ p = $\Delta$$\varPsi$ - 60 $\Delta$ pH
C) $\Delta$ pH = |pH_o - pHi|
D) both A and B
E) none of the above

Question 14

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) none of the above

Question 15

In the electron transport system, each cytochrome receives the electrons from a stronger __________ and transfers them to a stronger __________.

A) nitrogen compound series; sulfur compound series
B) reductant; oxidant
C) inorganic donor; organic donor
D) all of the above
E) none of the above

Question 16

The proton motive force drives the following process in bacteria:

A) ATP biosynthesis from ADP and Pi
B) flagellar rotation
C) nutrient uptake
D) all of the above
E) none of the above

Question 17

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 18

The chemiosmotic model does NOT explain synthesis of ATP in:

A) the chloroplast thylakoid membrane
B) the inner mitochondrial membrane
C) substrate-level phosphorylations
D) the purple bacteria thylakoids
E) inner membranes of Gram-negative bacteria

Question 19

NADH + H⁺ has more reducing power than FADH₂, therefore:

A) oxidation of NADH will contribute to form a larger $\Delta$ p and more ATP
B) oxidation of FADH₂ by respiratory ETS contributes less to $\Delta$ p formation, and as a consequence fewer ATP can be made
C) the NADH + H⁺/NAD⁺ redox pair has a more negative E°' value than the FAD/FADH₂ pair
D) all of the above
E) none of the above

Question 20

What are the units of E°'?

A) kJ/mol
B) kcal/mol
C) mV
D) ohm
E) faraday

Question 21

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

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

Question 22

Ferroplasma acidarmanus produces large amounts of sulfuric acid through:

A) oxidation of Cu⁺ with Cu(NO₃)₂
B) oxidation of FeS₂ with Fe³⁺
C) oxidation of Fe₃O₂ with Fe²⁺
D) all of the above
E) none of the above

Question 23

In seawater, sulfate is the most common anion after chloride. Which of the following is correct with respect to the use of sulfate by some 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) All of the above.

Question 24

Anaerobic corrosion of steel is accelerated by:

A) nitrifiers
B) sulfur-reducing bacteria
C) methanogenic archaea
D) all of the above
E) none of the above

Question 25

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

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

Question 26

Alkaliphiles maintain an inverted pH gradient in which:

A) the pH in their immediate environment is lower than the cytoplasmic pH
B) their immediate environment has a pH several units above that of the cytoplasm
C) pH in the immediate environment is equal to that of the cytoplasm
D) all of the above
E) none of the above

Question 27

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; nitrite can be absorbed by plants
C) anaerobic ammonium oxidation by nitrite; half the biosphere's nitrogen is returned as N₂ to the atmosphere
D) reduction of ammonium by oxygen; ammonium becomes ammonia
E) reduction of N₂ to ammonium; nitrogen atoms are incorporated into amino acids

Question 28

The reduction of uranium to uranite by Geobacter metallireducens is an example of:

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

Question 29

What is the chromophore group in bacteriorhodopsin?

A) tocopherol
B) $\beta$ -carotene
C) folic acid
D) retinal
E) none of the above

Question 30

Which organism oxidizes copper and iron sulfides?

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

Question 31

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

A) H₂SO₄; 2
B) H₃PO₄; 0
C) HCl; 1
D) CH₃COO^-; 4
E) none of the above

Question 32

Neisseria species are known to 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) None of the enzymes involved in dissimilatory reduction of nitrate are known from Neisseria.
E) none of the above.

Question 33

Bacterial activity in Earth's crust may have deposited most of the gold through the process of:

A) reduction of hydrosoluble Au³⁺
B) oxidation of Au³⁺
C) oxidation of gold ores
D) all of the above
E) none of the above

Question 34

Which of the following is correct with respect to dehalorespiration?

A) It is a type of hydrogenotrophy.
B) Cl^- can be removed from toxic compounds by dehalorespiration.
C) Hydrogenotrophs can be used in bioremediation.
D) All of the above.
E) None of the above.

Question 35

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) all of the above
E) none of the above

Question 36

In marine sediments, CO₂ is reduced to CH₄ by:

A) bacteria containing proteorhodopsin
B) oxygenic cyanobacteria
C) methanotrophic archaea
D) methanogenic archaea
E) none of the above

Question 37

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 38

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

A) Mg⁰/Mg²⁺
B) S⁰/S^2-
C) Cu⁺/Cu²⁺
D) Fe²⁺/Fe³⁺
E) none of the above

Question 39

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

A) the $\gamma$ drive shaft
B) the $\alpha$ proton channel
C) a ring of 12 c subunits
D) an $\alpha$$\beta$ -subunit
E) none of the above

Question 40

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) none of the above
E) all of the above

Question 41

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

Question 42

The chlorophyll chromophore consists of a heteroaromatic ring complexed to a:

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

Question 43

Which of the following is correct with respect to anaerobic photosystem I?

A) It can be found in chlorobia (the green sulfur bacteria) and chloroflexi (filamentous green bacteria).
B) It separates electrons associated with hydrogens from H₂S, HS^-, or H₂.
C) It separates electrons from Fe²⁺.
D) All of the above.
E) None of the above.

Question 44

What is the direction of the proton current in the chloroplast F₁F_o ATP synthase during ATP synthesis?

A) from stroma to cytoplasm
B) from cytoplasm to stroma
C) from lumen to stroma
D) from stroma to lumen
E) none of the above

Question 45

Which of the following is a common component of photolytic electron transport systems?

A) antennae system
B) electron carriers
C) energy carriers
D) all of the above
E) none of the above

Question 46

Why do electron transport systems have to occur within a membrane?

Question 47

In purple bacteria, bacteriochlorophylls are supplemented by accessory pigments called:

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

Question 48

Electricity production by metal-reducing bacteria is a possibility. Describe how a metal with multiple redox states can be used to produce an electrical current.

Question 49

What are facultative phototrophs? Provide an example and its possible use in biotechnology.

Question 50

Is the synthesis of ATP by the F₁F_o ATPase reversible? If so, are there any examples?

Question 51

Describe how an uncoupler functions. Can it be used as an antibiotic to treat bacterial infections?

Question 52

How has the Geobacter metallireducens redox energy been harnessed in the production of electricity?

Question 53

How does bacteriorhodopsin couple photoexcitation with proton pumping?

A) Bacteriorhodopsin has a proton channel domain.
B) Bacteriorhodopsin makes the membrane porous to protons.
C) Light-induced conformational changes of retinal cause the protein to extrude one proton.
D) All of the above.
E) None of the above.

Question 54

How can $\Delta$ p be measured in bacterial cells? Compare that with ways to measure it in eukaryotic cells.

Question 55

Describe Peter Mitchell's chemiosmotic model for coupling the electron transfer system with ATP synthesis.

Question 56

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

A) 65-700
B) 750-850
C) 800-1,100
D) all of the above
E) none of the above

Question 57

Electron donors for anaerobic photosystem I in green sulfur bacteria include:

A) H₂S
B) organic molecules
C) Fe²⁺
D) all of the above
E) none of the above

Question 58

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

A) H₂S; S⁰
B) O_2; H₂
C) O_2; H₂O
D) H₂O; H₂S
E) all of the above

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) none of the above

Question 60

Briefly discuss what factors may affect the relative contributions of the membrane potential ( $\Delta$$\varPsi$ ) and the proton gradient ( $\Delta$ pH) to $\Delta$ p.

Question 61

What could be the advantages of having a Na⁺-pumping oxidoreductase in pathogens such as Vibrio cholerae and Yersinia pestis?

Question 62

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

Question 63

What are nitrifiers? What damages and benefits may they have for human activities?

Question 64

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

Question 65

What is dissimilatory metal reduction? How is it different from assimilatory metal reduction?

Question 66

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 67

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

Question 68

What is photoheterotrophy? Give examples of photoheterotrophic organisms.

Question 69

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

Question 70

The F₁F_o 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?