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Phys-Pro - section 2 > Membrane energetics > Flashcards

Membrane energetics Flashcards

1
Q

Redox reactions are those in which electrons move from a ______ to a ______

A

from a donor (reductant/reducing agent) to an electron acceptor (oxidant/oxidizing agent).

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2
Q

What is the standard reduction (electrode) potential ?

A

The equilibrium constant for the redox reaction

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3
Q

What is the standard reduction potential a measure of?

A

the tendency of the reductant to lose electrons.

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4
Q

Oxidant/reductant pair is referred to as?

A

The redox couple

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5
Q

If the E’ is more negative, the compound is more likely to?

A

Donate electrons

  • act as the reductant
  • becomes oxidized
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6
Q

If the E’ is more positive, the compound is more likely to ?

A

Accept electrons

  • act as the oxidant
  • becomes reduced
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7
Q

Redox couples with more ____ reduction potentials will donate electrons to couples with more ____ potentials.

A

negative, positive

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8
Q

What is released when electrons move from a reductant to an oxidant with a more positive potential?

A

free energy (ΔGo’)

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9
Q

what is the equation for (ΔGo’) ?

A

ΔGo’ = -nFΔE’

where n = number of electrons transferred
F = Faraday constant (96.5 kJ/mole/volt)

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10
Q

What is ∆E?

A

E’ of reduction - E’ of oxidation

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11
Q

What are the 4 types of electron carriers?

A
  1. Flavoproteins
  2. Quinones
  3. Iron-sulphur proteins
  4. Cytochromes
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12
Q

What are flavoproteins? What kind of carriers are they?

A

Proteins with a flavin (which acts as the electron carrier)
-ex: FMN and FAD
Act as hydrogen and electron carriers

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13
Q

What are examples of quinones? What kind of carriers are they?

A

Coenzyme Q, ubiquinone

Act as hydrogen and electron carriers

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14
Q

What are iron-sulphur proteins and give 1 example? What kind of carriers are they?

A

FeS clusters within the proteins are the electron carriers
-ex: Ferredoxin

Act as electron carriers only

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15
Q

What are cytochromes? what kind of carriers are they?

A

use heme as the electron carrier.

Act as electron carriers only

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16
Q

How does FAD act as an electron carrier

A

Accepts 2 electrons and 2 protons to form FADH2

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17
Q

How do quinones act as electron carriers?

A

By accepting an electron and a proton to go from O- to OH

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18
Q

What are the 3 possible forms of ferredoxins?

A

2Fe2S, 3Fe4S, or 4Fe4S

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19
Q

What is the general structure of a heme group? What does this structure permit?

A

Highly conjugated ring system (which allows electrons to be very mobile) surrounding a metal ion

The metal ion readily converts between the oxidation states
-typically iron

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20
Q

which 3 complexes in the ETC are coupling sites?

A

Complexes I, III, and IV

  • coupled to proton extrusion
  • also called proton pumps
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21
Q

What happen at complex I ?

A

NADH is oxidized to NAD+ and 2 protons are pumped out

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22
Q

What happens at complex II?

A

FADH2 is oxidized to FAD+

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23
Q

What happens at complex III?

A

2 protons are pumped out

-electrons are transferred to complex 3 from ubiquinone in complex 2

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24
Q

What happens in complex IV?

A

electrons flow from cytochrome c to cytochrome a and then to cytochrome a3

finally transferred to O2 which is reduced to H20

2 protons are pumped out

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25
Q

How many protons are extruded if FADH2 is the electron donor

A

only 4 because you skip complex 1

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26
Q

In which 2 general ways do bacterial ETCs vary ?

A
  1. Vary among species

2. Vary among the same species under different growth conditions

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27
Q

Describe the general ETC for a bacteria under aerobic conditions (2 main points)

A
  1. Dehydrogenase complex removed electrons from an electron donor and transfers them to a quinone
  2. Transfer of electrons from the quinone to an oxidase complex via a branched pathway
    - depending on the bacteria the pathways may branch at the quinone or the cytochrome
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28
Q

Describe the general ETC for a bacteria under anaerobic conditions (3 steps)

A
  1. Dehydrogenase complex removed electrons from an electron donor and transfers them to a quinone
  2. Electrons transferred to reductase complexes
    - specific for each electron acceptor
  3. the final electron acceptor is an inorganic compound that insn’t oxygen
    - ex: fumarate and NO3-
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29
Q

How is light generated by photobacterium?

A

By diverting the flow of electrons from the usual ETC and into FMN

in the presence of an enzyme called luciferase and a long-chain hydrocarbon, the alternate chain emits light as it transfers electrons to O2

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30
Q

In the photobacteria producing light, which compounds are oxidized and which are reduced?

A

FMN and the hydrocarbon are oxidized and oxygen is reduced

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31
Q

Are free living photobacteria generally bioluminescent?

A

Not usually
- typically when they colonize the tissues of marine animals such as squid and fish that they use their light-generating pathway.

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32
Q

What special adaptation does the flashlight fish have?

A

(K. alfredi), has a special organ near its mouth that is specially adapted for the growth of luminescent bacteria.

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33
Q

What is oxidative phosphorylation ?

A

Process by which energy is used from the ETC to produce ATP

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34
Q

As many as __ ATP can be made when 2 electrons pass from NADH through to a molecule of O2

A

3 ATP

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35
Q

ATP synthesis is catalyzed by

A

F1F0ATPase

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36
Q

Which components of the F1F0ATPase are in the membrane and which are in the cytosol?

A

F0 is in the membrane

F1 is in the cytosol

37
Q

What is the role of F0

A

Almost identical to the flagellar motor

- where the protons enter

38
Q

What is the role of F1

A

where the binding change mechanism results in the formation of ATP

39
Q

How many ATP are made in the ETC from 1 molecule of glucose?

A

34

40
Q

What is the total amount of ATP produced from the complete oxidation of 1 molecule of glucose?

A

38

-ideal model

41
Q

How many NADH are produced in glycolysis?

A

2

42
Q

How many NADH are produced in the formation of acetyl-CoA and TCA cycle combined?

A

8

43
Q

How many FADH2 are produced in the TCA cycle?

A

2

44
Q

Who developed chemiosmotic theory?

A

Peter Mitchell

45
Q

What is the central idea of chemiosmotic theory?

A

energy-transducing membranes pump protons across the membrane, thereby generating an electrochemical gradient of protons across the membrane that can be used to do useful work when the protons return across the membrane to the lower potential

46
Q

The PMF (ΔP, mV) is defined as:

A

The sum of all forces (including proton concentrations) between the cytoplasm and outside the cell

47
Q

ΔΨ is?

A

Membrane potential

- constitutes all charged EXCEPT protons

48
Q

ΔpH is?

A

proton concentration across the membrane

49
Q

How is ∆pH calculated?

A

(pHi – pHo). pHi: cytoplasmic pH, pHo: external pH.

50
Q

Most bacteria balance the ∆pH and the ΔΨ such that the ∆P is between?

A

-60 to -200 mV

51
Q

∆P = ? (equation)

A

ΔP = ΔΨ - 60 ΔpH

52
Q

In neutrophiles ∆P is contributed by…?

A

Both ΔΨ and ΔpH.

53
Q

In acidophiles ∆P is contributed by…?

A

almost entirely by ΔpH

54
Q

In alkaliphiles ∆P is contributed by…?

A

almost entirely by ΔΨ

55
Q

How is ΔΨ measured?

A

Indirectly by using a cation plus an ionophore, or a lipophilic cation.

The cation accumulates in response to the membrane potential until equilibrium is reached.
ΔΨ = -60 log[(R+)in/(R+)out]mV.

56
Q

What is an inonophore?

A

compounds that perturb ion gradients by forming lipid-soluble complexes with cations
-rapidly equilibrate across the cell membrane.

57
Q

Equation for measuring ΔΨ

A

ΔΨ = - 60log10([ion]in/[ion]out)

58
Q

How is ∆pH usually measured?

A

By measuring the distribution of a weak acid of a weak base between the inside and the outside of the cell

On addition of a weak acid (or base) to a cell suspension, the uncharged molecule freely diffuses across the membrane and becomes deprotonated (or protonated).
AH –> A- + H+
or B + H –>BH+

At equilibrium, for a weak acid
Ka = [H+]in[A-]in/[AH]in = [H+]out[A-]out/[AH]out
where Ka is the dissociation constant

If pHin and pHout are at least 2 units higher than pKa, then most of the acid is ionized on both side of the membrane and [AH]in and [AH]out become negligible.
Then, ΔpH = log10[A-]in/[A-]out

59
Q

What practical accommodation is made when measuring ∆pH?

A

Using radioactive acid or base

60
Q

What are the 5 ways in which bacteria can generate a ∆P?

A
  1. Oxidation-recduction reactions
  2. ATP hydrolysis
  3. Sodium transport coupled to decarboxylation of a carboxylic acid.
  4. End product (e.g. lactate) efflux in symport with protons or sodium ions
  5. Light absorption by bacteriorhodopsin (photopigment) which functions as a proton pump
61
Q

What are 2 equations for ∆G (with respect to ∆P)

A 
∆G = -nF∆E'
∆G = yFΔP
62
Q

∆P = ? (using ∆G reactions)

A 
-nF∆E = yF∆P
∆P = -nF∆E/yF
63
Q

How does ATP hydrolysis contribute to ∆P?

A

Energy generated by hydrolysis of ATP is used to translocate protons to the outside.

64
Q

What equation is used to calculate the effect of ATP hydrolysis on ∆P?

A

∆G = yF∆P

  • used for protons going in and out of the cell
  • the ∆P is what you get for translocating 1 proton and hydrolyzing 1 ATP
65
Q

How is end product efflux used for generate a ∆P?

A

Can built up Na or H on the outside which can be useful as a gradient
- Can use end products of fermentation to do this like lactate in streptococcus

66
Q

How does bacteriorhodopsin contribute to the ∆P? What is its structure

A

acts as a proton pump

Large membrane protein with 7 transmembrane domains that form a channel

67
Q

Describe how bacteriorhodopsin acts as a proton pump? What pigment is involved?

A

Retinal (pigment) loses a proton when it is excited by light

Gains a proton from an asparatate which takes protons from the cytoplasm

= a proton has moved from the cytoplasm to outside

68
Q

What are lithotrophs?

A

chemotrophs that derive energy from the oxidation of inorganic compounds such as H2, CO, NH3, NO2-, H2S, or Fe2

69
Q

Many lithotrops are…?

A

aerobes

70
Q

Most lithotrops are also what kind of troph?

A

Autotrophs - use CO2 as the sole or major source of carbon.

- makes them chemolithoautotrophs

71
Q

What kind of oxidizers do not carry out reverse electron flow?

A

hydrogen oxidizers, sulfate oxidizers, and CO oxidizers

72
Q

Why do many organisms need to conduct reverse electron flow?

A

Because the the electron donors are more electropositive than the NAD+/NADH

73
Q

What are the 3 types of lithotrophs we discussed?

A
  1. Nitrite oxidizing
  2. Ammonia oxidizing
  3. Iron oxidizing
74
Q

Ammonia is _____in the environment and produced from ____

A

abundant ; deamination of amino acids, urea, or dissimilation of nitrate.

75
Q

Ammonia oxidizing bacteria are ____ that assimilate CO2 via the _______

A

Autotrophs; calvin benson cycle

76
Q

Ammonia oxidizing bacteria oxidize ammonia to ___ then to ____

A

Hydroxylamine which is then oxidized to nitrite

77
Q

What is generated during the oxidation of ammonia (besides the end products)?

A

2 net electrons and 6 protons are pumped to the periplasm

- generates ∆P

78
Q

Nitrite-oxidizing bacteria are ___ that oxidize nitrite to ____

A

Autotrophs; nitrate (NO3-)

79
Q

Nitrite-oxidizing bacteria work with what other bacteria to convert ammonia to nitrate?

A

Nitrifiers

-process called nitrification

80
Q

What kind of bacteria are important in the health of fish tank water?

A

nitrifying bacteria

81
Q

What are the 4 steps in the electron flow of a Nitrite-oxidizing bacteria?

A
  1. Nitrite is oxidized to nitrate generating 2 electrons
  2. Electrons also flow to O2 to generate a PMF
  3. ∆P drives electrons in reverse flow
  4. Reversed electron flow to reduce NAD+ to NADH
82
Q

What do iron-oxidizing bacteria accomplish?

A

Oxidize ferrous (Fe2+) to ferric (Fe3+) and derive energy from such an oxidation

83
Q

Most iron oxidizing bacteria are also what type of oxidizer?

A

acidophilic sulfur oxidizers that oxidize sulfide to sulfuric acid

84
Q

Where are iron-oxidizing bacteria usually found?

A

sites containing deposits of iron sulphide minerals where there is also water and oxygen

85
Q

What are iron-oxidizing bacteria also responsible for generating?

A

acid mine water

86
Q

What are the 4 steps in the electron flow of iron-oxidizing bacteria?

A
  1. Fe3+ oxidized to Fe2+
    - some electrons also flow to O2 (giving water) and to NAD+ (give NADH)
  2. Fe3+ reduced back to Fe3+ by S2-
    - the S0 generated is oxidized to SO4-(sulfuric acid)
    - electrons flow to NAD+ and O2
  3. Reversed electron flow to produce NADH
    - electrons are from Fe2+ oxidation and S0 oxidation.
  4. Protons are extruded generating a ∆P used to produce ATP and drive reversed electron flow to NAD+
87
Q

What are mine tailings?

A

Mine tailings are large piles of crushed rock that are left over after the metals of interest have been extracted from the mineral rocks

88
Q

How is acid mine water generated?

A

Iron leaches from mine tailings; iron-sulfur bacteria oxidize Fe2+ to Fe3+ resulting in lowering the pH of the water

Phys-Pro - section 2 (5 decks)

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