BIOL2210 mito ETC and ATP synth

where is the ETC located

inner mito memb

order of the ETC electron transfer components

from most negative to most positive standard reduction potential

hwat is the E rel from ETC redox reactions used for

to move protons from matrix to Intermemb spacer

examples of redox active molecules in the ETC

flavins

Fe-S centres

Quinones

cytochromes

Haems

Cu centres

difference between some redox active mols in ETC

some hydrogen carriers, some only electron carriers

are flavins hydrogen or electron carriers

hydrogen carriers

can carry 2 hydrogen

Are Fe-S clusters hydrogen or electron carriers

Electron carriers

Fe3+ > Fe2+

how are Fe-S clusters bound within complexes

sulfur in cluster form bonds with cysteine in protein

Complex 1

NADH-Q oxidoreductase

1 MDa in size with 14 central and 30 peripheral subunits (some mito encoded, others nuclear encoded)

redox chemistry induces conf changes that drive H+ pumping

4H+ pumped per pair of electrons

movement thru complex 1

has FMN (most negative) that accepts H from NADH

reduce Fe-S clusters (e carriers only)

till reduce ubiquinone (Q) (hydrogen carrier)

xomplex II

Succinate dehydrogenase

FADH2 is reduced

pass on electrons to ubiquinone via 3 FeS centres and heme b

NO PROTONS PUMPED

beneficial property of ubiquinone (coenzyme Q)

is lipid soluble so can pass within memb between complexes

mobile carrier between complexes

similarities between complex I and II

both reduce ubiquinone

have Fe-S clusters

how do diff cytochromes differ

in side chains on the porphyrin ring

how linked to protein (c by s-s but a and b non-cov)

(giving diff redox potentials)

strcture of cytochromes

porphrin ring with central coordinated Fe (via N atoms)

linked to protein via s-s (thioester) bonds to cysteines for cyt c, non cov link for a and b

xomplex III

Q-cytochrome C oxidoreductase

oxidises ubiquinol,

one ubiquinol reduces 2 cyt c mols

pumps 2 H+

(proton motive Q cycle)

does C III contain an unusually coordinated Fe-S cluster

yes, coord by cys and his (not just cys),

stabilises the reduced form (has more +ve reduction pot than norm) therefore increase its tendency to accept electrons

electron pathway thru complex III

The 2 e from QH2 take diff routes (from Q0 site where bind)

One via Reiske FeS centre and cytochrome c1 to cyt c

one via two cytochrome b’s to a second oxidised Q at Qi site

2H+ from QH2 rel into cytosol

second mol of QH2 req that reduces another cyt c and fully reduce the semiquinone in Qi site with uptake of 2 electrons from matrix

xomplex IV

cytochrome c oxidase

4 reduced cyt c + 4H+ from matrix with O2 mol > which form 4 oxidised cyt c and 2 water mols (terminal e acceptor)

e movement thru complex IV

red cyt c transf e to CuA, heme a, heme a3 (has Fe) to Cu B site.

second e transf from next cyt c to Fe in heme a3 site (so both heme a3 and Cu B site reduced)

O2 binds to reduced Fe and form peroxide bridge between heme a3 and Cu B (Fe and Cu inv)

o-o bond gets cleaved by reduction by another e from a cyt c, and H+ is taken up from matrix, further reduction by another cyt c causes take up another H+

final gain of 2 more H+ from matrix cause release of 2 H2O (now back to start)

why complex 4 causes large change in memp pot.

4 protons removed from matrix (form 2 water) and 4 pumped per 4 electrons transferred (per O2 reduced)

what is the Q cycle a solution to (C III)

getting ubiquinone that is a Hydrogen carrier to interact wit b type cytochromes that carry 1 electron

how are ETC and ATP synth coupled

by the proton gradient

(so inhib either and the other stops)

what does an uncoupler do

prov alternative route for H+ back thru memb, therefore uncouple ETC from ATP synth, as can remove proton gradient

structure of ATP synthase

f1 - 3 alpha (regulatory) and 3 beta (catalytic) subunits

gamma - connects F1 and F0

G0 - ring of Hphobic proteins that act as H+ channel

ATP synthase function

protons flow thru F0 channel it causes rotation. which drives rotation of gamma subunit, which drives conf change in alpha and beta subunits

sequential conf change in beta subunits as gamma rotates (binding change mechanims)

3 ATP per 360 o rotation

what is P:O ratio

describes how many mols of ATP made per O atom reduced to water

P:O ratio for NADH linked substrates vs FADH

lower for FAD (less ATP made per O reduced as pump less H+)

equation for number of protons for 1 ATP made

= number of c subunits/3 (as 1 rotation prods 3 ATP and each subunit transloc 1 e)