Oxidative phosphorylation

Question 1

what is oxidative phosphorylation?

Answer 1

where ATP formed as result of e- transfer from NADH or FADH2 to O2 by e- carriers

mitochondria in eukaryotes
cytoplasmic membrane in bacteria
generates 26/30 molecules of ATP

Question 2

mitochondrial structure

Answer 2

cristae impermeable to protons
gradient across membrane
respiratory proteins bounds within inner membrane of mitochondria

Question 3

how are the mitochondrial mechanically complex?

Answer 3

proton complexes in inner mitochondrial membrane
pumping H+ out of mitochondrial matrix

uneven distribution creates pH gradient & transmembrane electrical potential
proton motive force

Question 4

what is proton motive force used for?

Answer 4

to drive ATP synthesis

Question 5

how does oxidative phosphorylation work?

Answer 5

energy converted to different forms is always conserved

e- motive force converted to H+ motive force
proton motive force converted to phosphorylation transfer potential

just changing different forms of energy

Question 6

what are the e- driven proton pumps

Answer 6

NADH-Q oxioreductase
Q-cytochrome c oxioreductase
cytochrome c oxidase

Question 7

where are the redox centres?

Answer 7

quinones
flavins
iron-sulphur clusters
hemes
copper ions

large transmembrane complexes that contain multiple redox centres

Question 8

coupled transmembrane movement

Answer 8

oxidation andATP synthesis are coupled b transmembrane proton movement

process of e- transfer causes pump of protons

Question 9

what is the first e- carrier in the respiratory chain?

Answer 9

NADH-Q oxioreductase
takes e- from NADH and transfers them to Q

Question 10

what is NADH-Q oxioreductase?

Answer 10

structure consists of a membrane spanning part and long arm that extends into the matrix

NADH oxidised in the arm
e- transfered to reduced Q in the membrane

huge and very complex
half sits within membrane half outside

Question 11

what is the mechanism of NADH-Q oxioreductase

Answer 11

NADH + Q + 5H+ —> NAD+ +QH2 + 4H+

Question 12

what is the function of NADH-Q oxioreductase

Answer 12

transfer of 2e- from NADH to FMN
e- fro FMNH2 are transferred to series Fe-S clusters
e- from Fe-S clusters shuttles to Coenzyme Q
Q is reduced

Question 13

what is Q?

Answer 13

coenzyme

comes from NADH and FADH2
hydrophobic
diffuses rapidly within inner mitochondrial membrane
3 oxidation states

Question 14

what are the e- carriers in the respiratory chain?

Answer 14

succinate dehydrogenase
uses FADH2 as e- donor

Question 15

what is succinate dehydrogenase?

Answer 15

membrane protein of inner mitochondrial membrane
e- from FADH2 transferred to Fe-S clusters then to Q

doesn’t pump protons
less ATP formed by oxidation of FADH2 than NADH

Question 16

what I the second e- carrier in the respiratory chain?

Answer 16

Q-cytochrome c oxioreductase

Question 17

what is Q-cytochrome c oxioreductase

Answer 17

homo-dimer with 11 distinct polypeptide chains
3 heheh and a 2Fe-2S cluster

taking e- from Q and transferring them to cytochrome c

Question 18

what is the mechanism of Q-cytochrome c oxioreductase?

Answer 18

QH2 + 2Cytcox + 2H+matrix —> Q + 2Cytcred + 4H+cytosol

Question 19

what is the function of Q-cytochrome c oxioreductase?

Answer 19

catalyses transfer of e- from QH2 ro oxidised cytochrome
pumps protons out of mitochondrial matrix

Question 20

what is cytochrome c?

Answer 20

small soluble protein containing c-type heme
carries one e- from Q-cytochrome c oxioreductase to cytochrome c oxidase
reaction takes place twice

Question 21

what I the third e- carrier in the respiratory chain?

Answer 21

cytochrome c oxidase

Question 22

what is cytochrome c oxidase?

Answer 22

enzyme that has 13 polypeptide chains

prosthetic groups are:
Cua/ Cua
heme a
heme a3-cub
- heme a3-cub is site of reduction of oxygen to water

have multiple redox cofactors, copper and dinucleotide centre

Question 23

what I the mechanism of cytochrome c oxidase?

Answer 23

4Cytcred + 8H+matrix + O2 —> 4Cytcox + 2H2O + 4H+cytosol

4 chemical protons taken from matrix side to reduce one molecule of O2 to 2xH2O

4 pumped protons transported out of the matrix & released on cytosolic side in the course of reaction

Question 24

pumped protons

Answer 24

double efficiency of free energy storage in the form of a proton gradient
end of e- transfer

Question 25

what is atp synthase?

Answer 25

contains F1 subunits and Fo subunit

Question 26

what is the F1 subunit?

Answer 26

catalytic unit
5 types of polypeptide chains
a & b subunits makeup bulk
central stalk consists of 2 proteins

Question 27

what is the F0 subunit?

Answer 27

proton conducting unit
hydrophobic segment
spans inner mitochondrial membrane
contains proton channel of the complex
10c subunits and a subunit

Question 28

what is the mechanism of ATP synthase?

Answer 28

ADP3- + HPO4 2- + H+ <—> ATP4- + H2O

readily forms in absence of a proton motive force
ATP doesn’t leave catalytic site unless protons flow through enzyme
role of proton gradient is to release it from ATP synthase

need gradient for ATP to leave active site of the substrate
can only spin using proton motive force

Question 29

Inhibition of oxidative phosphorylation?

Answer 29

e- transport chain can be inhibited at various stages
coupling of e- transport and op disrupted by DNP

allows protons to flow back across membrane without going through ATP synthase

Question 30

what in an uncoupling protein?

Answer 30

in hibernating animals uncoupling of oxidative phosphorylation is a way of generating heat without synthesis of ATP