oxidative phosphoryaltion

five oligomeric complexes

• I NADH-ubiquinone (Q) oxidoreductase

• II succinate-ubiquinone (Q) oxidoreductase

• III ubiquinol- cytochrome c reductase

• IV cytochrome c oxidase

• V ATP synthase

ubiquinone

• oxidised form of coenzyme q

• aliphatic chain

• electrons are captured from the head

coenzyme q

• reduced one electron at a time

• semiquinone is a free radical from reduction of coenzyme q

  • reduced to dihydroquinone

  • which is then oxidised one electron at a time

complex i - enzyme and modules

• NADH-ubiquinone reductase

• largest of complexes

• nadh binds to dehydrogenase n module

• ubiquinone found in q module

• H+ move across the membrane arm P module

protons and electron movement with complex i

• two electrons from NADH transferred - oxidation to NAD+

• 4 protons move from mitochondrial matrix to the inter membrane space

  • against the conc gradient, nadh giving electrons to ubiquinone releases energy to allow this

• FMN acts as intermediate

complex ii properties and enzyme

• only enzyme common to citric acid cycle and respiratory chain

• does not move protons

• succinate Q reductase

electron movement and products from complex ii step

• FADH2 accepts the two electrons

• ubiquinone → ubiquinol

• succinate → fumarate releases two electrons to reduce FAD to FADH2 then ubiquinone to ubiquinol

cytochrome c

• electron carrier between complexes III and IV

• alpha helical haem protein, iron atom in the centre, does not bind oxygen

• small, highly soluble protein from the intermembrane space protein, associated to inner mitochondrial membrane

complex iii enzyme

ubiquinol-cytochrome c oxidoreductase

electron and protons transfer in complex iii

• 4 H+ are translocated, two from the matrix and two from QH2 using free eenrgy

• electrons are transferred from ubiquinol (QH2) to two molecules of cytochrome C - Q cycle

  • iron atom can change oxidative state in cytochrome C which allows the transfer of electrons

complex iv function

• receives electrons from cytochrome C carrier, one at a time

• iron atoms and copper atoms are both reduced and oxidised as electrons flow to oxygen

• catalyses the reduction of oxygen and water

• two more hydrogen ions are translocated using free energy

complex v enzyme, location and structure

• atp synthase

• found at the tips of the cristae

• knob and stalk structure

  • F1 - catalytic subunits (faces the matrix)

  • F0 - proton channel (embedded in the inner membrane)

proton movement for complex v

• use the proton gradient energy for the synthesis of ATP

• protons flow back into the matrix via ATP synthase

  • through rotation of proton channel and move up the stable ring

F1 subunits

• 3a, 3beta, 1 gamma, 1δ, 1ε

• alpha and beta alternate like orange segments

  • does not move

• gamma is main component of central axle and allows the rotation

• δ is in peripheral stalk

• each beta subunit has active site for ATP synthesis

rotational catalysis conformations for each beta unit

• open state - available to bind ADP and Pi

• loose state - active site closes loosely on ADP and Pi

• tight state - converts ADP and Pi into ATP

what drives the conformational changes of beta subunits for f1

flow of protons drive F0 and gamma rotation

this forces cyclic conformational changes to each beta subunit

number of protons per ATP

• one full rotation of ATP synthase - 3 molecules of ATP

• number of subunits in c ring of F0 = number of H+ needed for one full rotation

• number of H+ per ATP

• oxidative phosphorylation ~3H+/ATP

what transports atp, adp and pi

• adenine nucleotide translocate (antiporter)

• then pi enters through symport mechanism with H+

atp synthase stochiometry

P:O ratio = molecules of ADP phosphorylated / atoms of oxygen reduced

• 4H+ per ATP synthesised

• one H+ needed for transport of Pi across inner mitochondrial membran e

NADH: 2 e–, 10 H+ transported, ~2.5 ATP/O FADH2: 2 e–, 6 H+ transported, ~1.5 ATP/O