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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
How many protons are extruded if FADH2 is the electron donor
only 4 because you skip complex 1
26
In which 2 general ways do bacterial ETCs vary ?
1. Vary among species | 2. Vary among the same species under different growth conditions
27
Describe the general ETC for a bacteria under aerobic conditions (2 main points)
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
28
Describe the general ETC for a bacteria under anaerobic conditions (3 steps)
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-
29
How is light generated by photobacterium?
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
30
In the photobacteria producing light, which compounds are oxidized and which are reduced?
FMN and the hydrocarbon are oxidized and oxygen is reduced
31
Are free living photobacteria generally bioluminescent?
Not usually - typically when they colonize the tissues of marine animals such as squid and fish that they use their light-generating pathway.
32
What special adaptation does the flashlight fish have?
(K. alfredi), has a special organ near its mouth that is specially adapted for the growth of luminescent bacteria.
33
What is oxidative phosphorylation ?
Process by which energy is used from the ETC to produce ATP
34
As many as __ ATP can be made when 2 electrons pass from NADH through to a molecule of O2
3 ATP
35
ATP synthesis is catalyzed by
F1F0ATPase
36
Which components of the F1F0ATPase are in the membrane and which are in the cytosol?
F0 is in the membrane F1 is in the cytosol
37
What is the role of F0
Almost identical to the flagellar motor | - where the protons enter
38
What is the role of F1
where the binding change mechanism results in the formation of ATP
39
How many ATP are made in the ETC from 1 molecule of glucose?
34
40
What is the total amount of ATP produced from the complete oxidation of 1 molecule of glucose?
38 | -ideal model
41
How many NADH are produced in glycolysis?
2
42
How many NADH are produced in the formation of acetyl-CoA and TCA cycle combined?
8
43
How many FADH2 are produced in the TCA cycle?
2
44
Who developed chemiosmotic theory?
Peter Mitchell
45
What is the central idea of chemiosmotic theory?
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
The PMF (ΔP, mV) is defined as:
The sum of all forces (including proton concentrations) between the cytoplasm and outside the cell
47
ΔΨ is?
Membrane potential | - constitutes all charged EXCEPT protons
48
ΔpH is?
proton concentration across the membrane
49
How is ∆pH calculated?
(pHi – pHo). pHi: cytoplasmic pH, pHo: external pH.
50
Most bacteria balance the ∆pH and the ΔΨ such that the ∆P is between?
-60 to -200 mV
51
∆P = ? (equation)
ΔP = ΔΨ - 60 ΔpH
52
In neutrophiles ∆P is contributed by...?
Both ΔΨ and ΔpH.
53
In acidophiles ∆P is contributed by...?
almost entirely by ΔpH
54
In alkaliphiles ∆P is contributed by...?
almost entirely by ΔΨ
55
How is ΔΨ measured?
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
What is an inonophore?
compounds that perturb ion gradients by forming lipid-soluble complexes with cations -rapidly equilibrate across the cell membrane.
57
Equation for measuring ΔΨ
ΔΨ = - 60log10([ion]in/[ion]out)
58
How is ∆pH usually measured?
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
What practical accommodation is made when measuring ∆pH?
Using radioactive acid or base
60
What are the 5 ways in which bacteria can generate a ∆P?
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
What are 2 equations for ∆G (with respect to ∆P)
``` ∆G = -nF∆E' ∆G = yFΔP ```
62
∆P = ? (using ∆G reactions)
``` -nF∆E = yF∆P ∆P = -nF∆E/yF ```
63
How does ATP hydrolysis contribute to ∆P?
Energy generated by hydrolysis of ATP is used to translocate protons to the outside.
64
What equation is used to calculate the effect of ATP hydrolysis on ∆P?
∆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
How is end product efflux used for generate a ∆P?
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
How does bacteriorhodopsin contribute to the ∆P? What is its structure
acts as a proton pump Large membrane protein with 7 transmembrane domains that form a channel
67
Describe how bacteriorhodopsin acts as a proton pump? What pigment is involved?
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
What are lithotrophs?
chemotrophs that derive energy from the oxidation of inorganic compounds such as H2, CO, NH3, NO2-, H2S, or Fe2
69
Many lithotrops are...?
aerobes
70
Most lithotrops are also what kind of troph?
Autotrophs - use CO2 as the sole or major source of carbon. | - makes them chemolithoautotrophs
71
What kind of oxidizers do not carry out reverse electron flow?
hydrogen oxidizers, sulfate oxidizers, and CO oxidizers
72
Why do many organisms need to conduct reverse electron flow?
Because the the electron donors are more electropositive than the NAD+/NADH
73
What are the 3 types of lithotrophs we discussed?
1. Nitrite oxidizing 2. Ammonia oxidizing 3. Iron oxidizing
74
Ammonia is _____in the environment and produced from ____
abundant ; deamination of amino acids, urea, or dissimilation of nitrate.
75
Ammonia oxidizing bacteria are ____ that assimilate CO2 via the _______
Autotrophs; calvin benson cycle
76
Ammonia oxidizing bacteria oxidize ammonia to ___ then to ____
Hydroxylamine which is then oxidized to nitrite
77
What is generated during the oxidation of ammonia (besides the end products)?
2 net electrons and 6 protons are pumped to the periplasm | - generates ∆P
78
Nitrite-oxidizing bacteria are ___ that oxidize nitrite to ____
Autotrophs; nitrate (NO3-)
79
Nitrite-oxidizing bacteria work with what other bacteria to convert ammonia to nitrate?
Nitrifiers | -process called nitrification
80
What kind of bacteria are important in the health of fish tank water?
nitrifying bacteria
81
What are the 4 steps in the electron flow of a Nitrite-oxidizing bacteria?
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
What do iron-oxidizing bacteria accomplish?
Oxidize ferrous (Fe2+) to ferric (Fe3+) and derive energy from such an oxidation
83
Most iron oxidizing bacteria are also what type of oxidizer?
acidophilic sulfur oxidizers that oxidize sulfide to sulfuric acid
84
Where are iron-oxidizing bacteria usually found?
sites containing deposits of iron sulphide minerals where there is also water and oxygen
85
What are iron-oxidizing bacteria also responsible for generating?
acid mine water
86
What are the 4 steps in the electron flow of iron-oxidizing bacteria?
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
What are mine tailings?
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
How is acid mine water generated?
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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