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Microbiology > Chapter 14 > Flashcards

Chapter 14 Flashcards

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1
Q

How do microbes transfer energy?

A

By moving electrons

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2
Q

generates a “proton motive force” that drives protons across the membrane

A

electron transport system

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3
Q

stores energy to make ATP.

A

Proton motive force

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4
Q

Most energy-yielding reactions involve transfer of
electrons from a

A

reduced electron donor to an
oxidized electron acceptor

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5
Q

transfer of electrons occurs through a series of membrane-soluble carriers called an electron transport system (ETS)/Electron transport chain

A

aerobic respiration

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6
Q

What are the three major classes of prokaryotic energy acquiring processes using the ETS

A
  1. Organotrophy
  2. Lithotrophy
  3. Phototrophy
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7
Q

involves organic electron donors and inorganic
or organic terminal electron acceptors

A

Organotrophy

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8
Q

involves inorganic electron donors and inorganic or
organic terminal acceptors

A

Lithotrophy

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9
Q

Involves light capture by chlorophyll, usually coupled to the splitting of H2S or H2O or organic molecules

A

Phototrophy

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10
Q

A reaction is favored by

A

positive values of E, which
yield negative values of DG.

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11
Q

What is reduction potential (E)?

A

It is a measure of the tendency of a molecule to accept electrons.

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12
Q

How are ΔG and E related in redox reactions?

A

ΔG values are proportional to the difference in reduction potential between the electron donor and acceptor.

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13
Q

What does a negative ΔG mean in a redox reaction?

A

The reaction is energetically favorable.

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14
Q

What does a high (positive) reduction potential mean about a molecule?

A

It has a strong tendency to accept electrons (good electron acceptor).

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15
Q

What is the proton motive force (PMF)?

A

It is the electrochemical gradient of protons (H⁺) generated across a membrane by a proton pump.

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16
Q

What drives the creation of the proton motive force?

A

The transfer of H⁺ through a proton pump in the electron transport system (ETS).

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17
Q

What is the main purpose of the proton motive force?

A

To drive the conversion of ADP to ATP via ATP synthase.

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18
Q

What is the name of the process that uses the proton motive force to synthesize ATP?

A

The chemiosmotic theory.

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19
Q

Which enzyme uses the proton motive force to make ATP?

A

ATP synthase (F₀F₁ complex).

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20
Q

What happens to protons (H⁺) after they are pumped across the membrane?

A

They flow back through ATP synthase, powering ATP production.

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21
Q

What are the two forms of energy stored when protons are pumped across the membrane?

A

Electrical potential and pH difference.

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22
Q

What causes the electrical potential in the proton motive force?

A

Separation of charge between the cytoplasm and the external solution.

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23
Q

What causes the pH difference in the proton motive force?

A

The difference in H⁺ concentration between the inside and outside of the cell membrane.

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24
Q

How is the pH difference quantified?

A

As the log ratio of external to internal chemical concentration of H⁺.

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25
Where is the proton concentration higher in a typical PMF setup?
Outside the membrane (acidic, more H⁺), compared to the cytoplasm (basic, less H⁺).
26
What is the proton motive force (PMF) used to generate inside the cell?
ATP, via F₀F₁ ATP synthase
27
How does the PMF contribute to drug resistance in bacteria?
It powers drug efflux pumps, which expel toxic compounds from the cell.
28
Which cellular motor is powered by the proton motive force?
The bacterial flagellum (for rotation/movement).
29
Name three types of transport proteins powered by the PMF.
Uniport (moves one type of ion/molecule) Symport (moves two substances in the same direction) Antiport (moves two substances in opposite directions)
30
What role does the electron transport system (ETS) play in PMF generation?
The ETS pumps protons across the membrane, creating the gradient that powers the PMF.
31
Where does the PMF accumulate protons?
On the outside of the cell membrane (or the periplasm in Gram-negative bacteria).
32
33
transfer electrons ultimately to O2, producing H2O.
NADH and FADH2
34
What is the role of cofactors in the electron transport system (ETS)?
Cofactors mediate electron transfer by enabling small energy transitions in ETS proteins like cytochromes.
35
What type of proteins commonly use cofactors for electron transfer?
Cytochromes and other ETS proteins.
36
What kinds of molecular structures are typically involved in energy transitions mediated by cofactors?
Metal ions (e.g., iron or copper) Conjugated double bonds and heteroaromatic rings
37
How are metal ions stabilized in ETS proteins?
They are held in place by amino acid residues.
38
What is an example of a heteroaromatic ring involved in energy transitions?
The nicotinamide ring of NAD⁺/NADH.
39
What is the function of flavin mononucleotide (FMN) in the electron transport system?
FMN acts as an electron carrier and participates in redox reactions.
40
What amino acid binds iron-sulfur clusters in proteins?
Cysteine (through its sulfur atom).
41
What is required to build an ETS?
1. An initial substrate oxidoreductase (or dehydrogenase) 2. A mobile electron carrier 3. A terminal oxidase
42
What is the function of the NADH:quinone oxidoreductase complex?
It transfers electrons from NADH to quinone (Q), while pumping protons (H⁺) across the membrane to generate the proton motive force.
43
What cofactor first accepts electrons from NADH in this complex?
Flavin mononucleotide (FMN).
44
What happens to NADH during this process?
NADH is oxidized to NAD⁺, releasing 2 electrons and 1 proton (H⁺).
45
What electron carriers are used within the NADH:quinone oxidoreductase complex?
FMN, iron-sulfur clusters ([4Fe-4S]), and ubiquinone/ubiquinol.
46
What is the reduced form of ubiquinone?
Ubiquinol.
47
How many protons are pumped across the membrane by this complex per NADH?
4 protons (H⁺).
48
What is the role of iron-sulfur clusters in this complex?
They shuttle electrons from FMN to ubiquinone.
49
What type of proteins make up the ETS?
Oxidoreductases – enzymes that facilitate redox reactions.
50
What are cytochromes?
Colored proteins in the ETS that shift absorbance spectra when their redox state changes.
51
What role does the quinone pool play in the ETS?
It transfers electrons from NDH-1 to cytochrome bo while shuttling protons across the membrane.
52
What is the final electron acceptor in aerobic respiration?
Oxygen (O₂), which is reduced to H₂O.
53
How many total protons are pumped per NADH in this ETS pathway?
8 protons (4 by NDH-1 and 4 by cytochrome bo complex via quinone cycle).
54
What complex in the ETC oxidizes NADH?
Complex I (NADH dehydrogenase)
55
What is the role of Complex II (succinate dehydrogenase)?
It oxidizes FADH₂ to FAD and transfers electrons to ubiquinone (Q).
56
Which complexes pump protons (H⁺) into the intermembrane space?
Complex I, Complex III, and Complex IV.
57
What is the final electron acceptor in the mitochondrial ETC?
Oxygen (O₂), which is reduced to H₂O at Complex IV
58
What mobile electron carriers shuttle electrons between complexes?
Ubiquinone (Q) between Complexes I/II and III Cytochrome c between Complexes III and IV
59
What is the function of the F₁F₀ ATP synthase complex?
It synthesizes ATP using the energy from the proton motive force (PMF) as protons flow through it.
60
What are the two major parts of the ATP synthase complex?
F₀: Membrane-bound, pumps protons F₁: Cytoplasmic, generates ATP
61
How does proton movement drive ATP synthesis in this complex?
Proton flow through F₀ causes rotation, which induces conformational changes in F₁ that catalyze ATP synthesis.
62
What molecule rotation is driven by H⁺ flux in ATP synthase?
The γ (gamma) subunit rotates inside the F₁ complex, facilitating ATP production.
63
What are obligate aerobes?
Organisms that grow only when using O₂ as the terminal electron acceptor.
64
What types of organisms are obligate aerobes?
Animals, plants, and many bacteria.
65
What do prokaryotes use instead of O₂ in anaerobic respiration?
Metals, oxidized nitrogen ions, and sulfur compounds as terminal electron acceptors.
66
Under what conditions does anaerobic respiration usually occur?
In environments where oxygen is scarce.
67
What is the difference between aerobic and anaerobic respiration in terms of electron acceptors?
Aerobic uses oxygen (O₂); anaerobic uses alternative acceptors like metals or nitrogen/sulfur compounds.
68
Anaerobic respiration is unique to
prokaryotes.
69
Why is anaerobic respiration unique to prokaryotes
They usually possess alternative electron donors and electron acceptors
70
What is the full reduction sequence of nitrate (NO₃⁻) in anaerobic respiration?
NO₃⁻ → NO₂⁻ → NO → ½ N₂O → ½ N₂ (nitrate → nitrite → nitric oxide → nitrous oxide → nitrogen gas)
71
Can most microbes complete the full nitrate reduction sequence?
No, most species can only perform one or two transformations in the series.
72
What microbial process uses nitrogen or sulfur compounds as electron acceptors?
Anaerobic respiration
73
What is the end product of sulfate reduction?
Hydrogen sulfide (H₂S)
74
What is the end product of complete nitrate reduction?
Nitrogen gas (N₂)
75
What is lithotrophy (or chemolithotrophy)?
It is the acquisition of energy by the oxidation of inorganic electron donors.
76
What is an example of a molecule used in lithotrophy?
Hydrogen gas (H₂) or ferrous iron (Fe²⁺).
77
What do some organotrophs use to conduct lithotrophy?
Alternative oxidoreductases that oxidize inorganic molecules like H₂ or Fe²⁺.
78
What are obligate lithotrophs?
Bacteria that oxidize only inorganic molecules for energy.
79
What types of organisms are lithotrophs?
Nearly all are bacteria or archaea.
80
What kind of microbial metabolism involves nitrogen and sulfur oxidation?
Lithotrophy (specifically, chemolithotrophy)
81
What is the sequence of nitrogen oxidation?
NH₄⁺ → NH₂OH → HNO₂ → HNO₃ (ammonium → hydroxylamine → nitrous acid/nitrite → nitric acid/nitrate)
82
What is the starting compound in nitrogen oxidation?
Ammonium (NH₄⁺)
83
What is the final product of nitrogen oxidation?
Nitric acid (HNO₃) / nitrate
84
What is the final product of sulfur oxidation?
Sulfuric acid (H₂SO₄)
85
What role do these compounds (like H₂S and NH₄⁺) play in lithotrophy?
They serve as inorganic electron donors that are oxidized for energy.
86
What is a hidden hazard caused by anaerobic sulfur and iron reactions?
Corrosion of steel in underwater bridge supports and other human structures
87
What type of bacteria contributes to iron corrosion under anaerobic conditions?
Sulfur-reducing bacteria
88
How do sulfur-reducing bacteria initiate corrosion?
They reduce elemental sulfur (S⁰) to hydrogen sulfide (H₂S) using H₂.
89
What happens when iron reacts with hydrogen sulfide (H₂S)?
Fe + H₂S → FeS + H₂ — Iron forms iron sulfide (FeS) and hydrogen gas.
90
What compound precipitates on the corroded surface during anaerobic iron oxidation?
Iron sulfide (FeS)
91
What role does sulfate (SO₄²⁻) play in iron corrosion?
It is reduced to FeS and hydroxide ions (OH⁻), promoting further corrosion.
92
What is hydrogenotrophy?
It is the use of molecular hydrogen (H₂) as an electron donor in microbial metabolism.
93
Why is H₂ an effective electron donor?
Because it has a sufficiently negative reduction potential to donate electrons to nearly all biological electron acceptors.
94
What is dehalorespiration?
A type of hydrogenotrophy where chlorinated organic molecules are used as electron acceptors, often useful in bioremediation.
95
What environmental role does hydrogenotrophy play?
It supports anaerobic respiration and contributes to the removal of toxic chlorinated compounds in polluted environments.
96
the reduction of CO2 and other single-carbon compounds to methane.
Methanogenesis
97
What organisms perform methanogenesis?
Only archaea called methanogens.
98
What are methanotrophs?
Prokaryotes that oxidize methane (CH₄) using a terminal electron acceptor (TEA) such as O₂, nitrate, or sulfate.
99
How are methanogenesis and methanotrophy related?
Methanogenesis produces methane, which serves as a substrate for methanotrophs in ecosystems.
100

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