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MBB266 > Poole (Biological energy transformations) > Flashcards

Poole (Biological energy transformations) Flashcards

1
Q

How much ATP does an adult convert per day at diff activity levels?

A
  • rest = 1/2 body weight ATP
  • normal = body weight ATP
  • hard work = up to 1 ton ATP
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2
Q

What did Mitchell propose?

A
  • chemiosmotic hypothesis

- link between e- transport phosphorylation need NOT involve chemical intermediates

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3
Q

How does chemiosmosis underpin all contemporary thought in bioenergetics?

A
  • redox reactions –> transmembrane grad

ATP synthesis

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4
Q

What is chemiosmosis?

A
  • partially permeable membrane separates 2 solutions w/ v diff concs
  • water moves through membrane to equalise concs
  • at non eq distribution coupling device driven by H+ movement down ec grad and uncoupled leak of H+
  • piston could be trying to push water back the way it came
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5
Q

How is ox and phosphorylation chemiosmotically coupled?

A
  • resp chain extrudes protons
  • gen ec pot across membrane (interior alkaline and +ve)
  • return of protons through ATP synthase coupled to ATP formation
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6
Q

What is the structure of mito membrane?

A
  • IM folded into cristae

- periplasm between IM and OM

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7
Q

What do P and N mean w/ respect to unfractionated bacterium?

A
  • P = +ve phase, periplasm

- N = -ve phase, cyto

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8
Q

In fractionated bacterium what are P and N phase?

A
  • lysozyme and osmotic shock = right side out vesicle (N inside)
  • French press = inside out vesicle (P inside)
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9
Q

How can mito membranes be prepped?

A
  • ultrasonication yields particles analogous to everted bacterial vesicles
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10
Q

In mito membranes which is P and N phase?

A
  • P phase = IMS

- N phase = matrix

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11
Q

What 3 stages do all novel ideas in science pass though?

A

People say:

  • not true
  • true but not important
  • true and important but not new
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12
Q

What is the physical reality of ‘energised state’ of, eg. a mito?

A
  • ‘activated chemical intermediates’
    • -> redox reaction creates high energy intermediate w/ assoc phosphate, but couldn’t figure out what P was
  • or charged particles w/in membrane
  • or pmf across membrane, ie. chemiosmosis
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13
Q

What are the major points of chemiosmosis?

A
  • metabolic reactions that energise membrane gen ec grad across it
  • resp chains, photosynthetic centres and ATP synthase all cat proton translocation
  • polarity of pot not always +ve
  • energy coupling req topologically closed membrane (vesicle)
  • reagents of mutations that dissipate proton circulation also de-energise membranes
  • membrane can be energised by imposing ‘artificial’ grad of pH or electrical pot
  • accum of many metabolites accompanied by proton movements
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14
Q

How is pmf calculated?

A
  • Δp (mV) = Δψ - 61ΔpH

- Δψ is charge diff across membrane

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15
Q

Why measure driving forces?

A
  • quantitative approach will exorcise mistaken idea that ATP magical ‘high energy compound’
  • can calc conditions req for eq and how far a reaction is displaced from eq
  • displacement defines capacity of reaction to perform useful work
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16
Q

How does Gibbs energy and entropy vary in diff systems?

A
  • isolated system = no exchange of energy and materials
  • closed system = ΔH, heat flows
  • open system = living systems exchange energy w/ surroundings
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17
Q

What is the Gibbs equation?

A
  • ΔG = ΔH - TΔS
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18
Q

What does a value of less than 0 for ΔH mean?

A
  • net increase in entropy of system and surroundings

- ∴ spontaneous process

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19
Q

How can Gibbs energy constant be observed as a function of its displacement from eq?

A
  • if push reaction further away from eq, Gibbs energy changes
  • if put energy in poss to move reaction left/right and increase Gibbs
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20
Q

Does the eq constant (K) have units?

A
  • yes unless no. product molecules = no. substrate molecules
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21
Q

What relation must K and T (temp constant) have in order for ΔG to be +ve/-ve?

A
  • ΔG -ve if TK
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22
Q

How can ΔG be calc using mass action ratio?

A
  • ΔG = -2.3RT log10 [K/Γ)
  • R = gas constant
  • T = temp constant
  • Γ = observed mass action ratio
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23
Q

What does the equation ΔG = -2.3RT log10 [K/Γ) tell us about ΔG?

A
  • has value that is function of displacement from eq

- means 37° reaction maintained 1 order of magnitude from eq has ΔG of 5.9kJ/mol

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24
Q

Are spontaneous/non spontaneous processes reversible?

A
  • spontaneous = only reversible w/ difficulty

- non spontaneous = reversible

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25
Q

How does cell make reactions spontaneous in matrix and cyto?

A
  • pushes reaction away from eq
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26
Q

What defines the capacity of reactants to do work?

A
  • extent to which observed Γ displaced from eq
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27
Q

Why is the high energy phosphate bond a myth?

A
  • hypothetical cell could utilise any reaction to transduce energy from mito, if maintained certain no. orders from eq
  • but is important that eq constant for ATP hydrolysis has approx value it does, as provides sufficient driving force for many +ΔG processes
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28
Q

What is membrane pot?

A
  • diff in electrical pot between 2 aq compartments separated by membrane
29
Q

How is ΔpH defined?

A
  • pH in P phase - pH in N phase
30
Q

In respiring mito is ΔpH usually +ve or -ve?

A
  • -ve
31
Q

How is Δψ defined, and is it usually +ve or -ve?

A
  • P-phase - N-phase

- usually +ve

32
Q

What can Δp be made up of?

A
  • ΔpH and Δcharge (more H+ on 1 side)
  • Δcharge only (more +ve ions on 1 side, same no. H+)
  • ΔpH only (same no +ve ions, more H+ on 1 side)
33
Q

What is DNP, and why is it dangerous?

A
  • an uncoupling agent (protonophores)

- allows H+ in mito to link back to other side w/o doing useful work

34
Q

What is a protonophore?

A
  • proton carrier
35
Q

What is an ionophore?

A
  • carriers of ions across membrane
36
Q

When are ATP, ADP and inorganic phosphate no use?

A
  • when at equilibrium
37
Q

What is the structure of ATPase?

A
  • F1 is catalytic part –> formed by α3 β3 hexamer w/ γ subunit inside it, and ε attached to γ
  • subunit δ bound to ‘top’ of hexamer and subunits b
  • hydrophobic transmembrane segment of b in contact w/ a
  • γ and ε bound to ring shaped oligomer of c-subunits
  • proton translocation takes place at interface of subunits a and c
38
Q

What is the catalytic mechanism of ATPase?

A
  • rotary catalysis

- involves rotation of γ subunit w/ ε and c subunit oligomer relative to rest of enzyme

39
Q

What is the binding change mechanism for ATP synthesis?

A
  • DIAGRAM*
  • central asymmetric cam rotates in step 1 relative to 3 α/β subunit pairs
  • forces 3 catalytic sites to undergo conformational changes
  • tight = where ATP made
  • loose = where substrates come in and bind
  • open = substrates ADP+Pi can easily come in
40
Q

How is ATP made?

A
  • pmf drives protons through –> drives rotation of c-subunit oligomer ring relative to α and β subunits
  • rotation passed to γ and ε bound to c-subunit oligomer ring
  • rotation of asymmetric γ mechanistically causes conformational changes in αβ hexamer, each 120°γ rotation forces 1 of 3 catalytic sites located at αβ interface into open conformation
  • freshly synthesised ATP released and ADP+Pi bound instead, high affinity of opened site to phosphate impairs ATP rebinding and favours ADP binding
  • rotation cont, forcing next site into open conformation, ADP+Pi bound to previous O site occluded and ATP synthesis occurs
  • ATP formed released when γ makes 1 360° turn and once again open site
41
Q

What have more recent experiments revealed about how ATP is made?

A
  • that if γ mechanistically forced into rotation, ATP synthesis takes place even w/o proton translocating F0 part
42
Q

How many protons req to make ATP?

A
  • complete 360° req passage of no. of protons = no. of subunits
  • generally agreed that 1 rotation of γ w/in αβ synthesises 3ATP
  • so H+/ATP might be 3.3 (ie. 3H+ needed to make 1ATP
43
Q

What does no H+ req to make ATP depend upon?

A
  • no. c-subunits
44
Q

What input of Gibbs energy is req to maintain [ATP]/[ADP] ratio?

A
  • 57kJ/mol to keep ratio 10^10 away from eq
45
Q

What are the muscles of inspiration?

A
  • accessory = sternocleidomastoid, scalenes group, pectoralis major
  • principal = external intercostals, diaphragm
46
Q

What are the muscles of expiration?

A
  • quiet breathing = passive elastic recoil of lungs, rib cage and diaphragm
47
Q

Is it poss to reverse molecular respiration?

A
  • yes, if put energy into system

* DIAGRAM*

48
Q

What is cytochrome c?

A
  • soluble e- carrier in mito/bacteria etc.

- most widely used e- transporters

49
Q

What is the structure of cytochrome c?

A
  • haem in centre
  • square planar structure w/ central Fe, coord by 4 pyrrole rings
  • Fe cycles between Fe(II), Fe(III) and occasionally Fe(IV)
  • same prosthetic group in Hb and myoglobin
50
Q

What is ubiquinone?

A
  • lipid soluble carrier of H
51
Q

What is the e- tower of redox pots?

A
  • in general e-s flow from -ve to +ve redox pot
52
Q

What is the redox reaction of cytochrome c?

A
  • cyt c [Fe(III)] + e- cyt c [Fe(II)]
53
Q

What is the redox reaction of ubiquinone (UQ)?

A
  • UQ + 2e- + 2H+ UQH2
54
Q

What is the biggest redox pot in most mito and bacteria?

A
  • NAD+/NADH to 1/2O2/H2O
55
Q

What are the diff redox carriers (complexes) in mito chain?

A
  • complex I = NADH deHase, FMN, 8 Fe/S centres
  • complex II = succinate deHase, FAD, 3Fe/S, haem b
  • complex III = cytochrome bc, complex II haem b, Fe/S, c1
  • complex IV = 2x haem a, 3 Cu
56
Q

What is the pathway of redox carriers in mito chain?

A
  • complex I, glycerol-3-P-deHase and complex II feed into UQ/UQ2 pool
  • feeds to complex III
  • then to complex IV
57
Q

Does H+ pumping in mito chain exceed H+/ATP ratio of 3?

A
  • yes, greatly exceeds it
58
Q

Do e- carriers all ox or red?

A
  • rarely, grad of e- occupancy
59
Q

Unlike mito resp chain, resp apparatus of bacteria is what?

A
  • highly flexible
60
Q

How is the resp apparatus of bacteria flexible?

A
  • modular –> mix and match assembly of components put together to achieve particular function
  • numerous deHases, several types of quinones, 3 oxidases and numerous anaerobic reductases
  • so system must be branched
  • composition and ∴ function is controlled by circuits of gene reg in response to growth conditions
61
Q

Is NADH deHase of E. Coli a proton pump?

A
  • yes
62
Q

What is the 1st terminal oxidase of E. Coli?

A
  • cytochrome bo’ or Cyo, a proton pump

- H+/e- = 2

63
Q

What is the result of coupling NADH deHase to cytochrome bo’?

A
  • makes efficient proton pumping resp chain
64
Q

What are the 2nd and 3rd oxidases of E. Coli, and what is there role?

A
  • NOT pumps, but DO translocate protons
  • structurally and functionally similar
  • 2nd is CydAB
  • 3rd is AppBC or bd-II
  • spatially separate e- and H+ from ubiquinol
  • H+/e- = 1
65
Q

How can energy conservation be manipulated?

A
  • expression of diff deHases and oxidases

- routes reg at level of gene expression

66
Q

What are the characteristics of Azotobacter vinelandii?

A
  • obligate aerobe
  • carries out N fixation which is v O sensitive
  • has 1 of highest resp capacities known
  • removes internal O by phenomenal oxidase activity of cytochrome bd
  • bd mutant cannot grow by N fixation in air
67
Q

What are the energetics of growth at pH 1-3?

A
  • favourable pH grad
  • balanced by internal +ve membrane pot due to K+
  • to help prevent massive proton influx a membrane pot is used
68
Q

What are energetics of an alkaliphile based on N+ circulation?

A
  • resp chains pump Na+ not H+
  • decarboxylase pumps Na+ outwards to contribute to Na grad
  • ATP synthase and flagellar rotation driven by Na+ flux
  • antiporter used to exchange Na+ for H+
69
Q

How does pmf have a central role in bacteria w/ diff lifestyles?

A
  • resp and glycolysis in facultative like E. Coli
  • fermentative metabolism only, in bacteria like streptococci and clostridia
  • photolithotrophic metabolism in green and purple sulphur bacteria

MBB266 (7 decks)

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