Oxidative Phosphorylation Flashcards
What happens during oxidative phosphorylation?
Electrons are transferred through electron carriers
Process generates a proton gradient for ATP synthase
Where does oxidative phosphorylation take place?
Inner mitochondrial membrane
More acidic in the ___________
Intermembrane space
What are 4 examples of electron carriers?
- NAD and FAD
- Ubiquinone/Coenzyme Q
- Cytochromes
- Iron-sulphur proteins
What are the properties of ubiquinone/coenzyme Q?
- Fat-soluble so able to move through membrane
- Can accept 1 or 2 electrons
What are cytochromes?
Iron heme-containing proteins that act as an electron carrier
What are the 3 types of cytochromes involves in oxidative phosphorylation? Are they membrane-bound or soluble?
- A is membrane-bound
- B is membrane-bound
- C is soluble
What is the basic formation of iron-sulphur proteins?
Fe and S coordinates with 4 cysteine residues from a protein
Complex I: where are the electrons transferred?
NADH to ubiquinone
Structure of complex I
- 42 polypeptide chains
- 6 iron-sulphur centres
What is formed at complex I and where does it diffuse to?
Ubiquinol diffuses to complex III
Complex II: where are the electrons transferred?
Succinate to ubiquinone
What happens at complex II?
Electron is removed from succinate and transferred to FAD then to ubiquinone to form ubiquinol
Complex III: where are the electrons transferred?
Ubiquinone to cytochrome c
What is the problem with the reaction at complex III and how is it overcome?
Cytochrome c can only accept 1 electron but ubiquinone donates 2 electrons so there’s a process called the Q cycle
What is the Q cycle?
1 electron is transferred to cytochrome c and the other electron is recycled through the complex forming semi-ubiquinone
Complex IV: where are the electrons transferred?
Cytochrome c to O2
What is the relation between the inter membrane space and complex I and IV?
4 protons are pumped into the inter membrane space
What is formed at complex IV?
H2O
During the formation of H2O in Complex IV of oxidative phosphorylation what is consumed? What is the significance of this?
- 4 protons are consumed from inside the mitochondria
- This helps to amplify the proton gradient across the inner mitochondrial membrane
What does ATP synthase act as a pore for?
Hydrogen ions
What are the subunits of ATP synthase and what are their functions?
F1 - ATPase for formation
F0 - membrane-embedded portion which acts as a pore for protons to pass through to drive ATPase
What makes up the F1 subunit?
ß units, present in 3 states
What are the 3 states of the ß units?
Empty
ADP
ATP
What is bound at each state of the ß units?
Empty - nothing bound
ADP - ADP and Pi bound, loose
ATP - ATP-bound, tight configuration
How does the movement of protons through ATP synthase drive ATP formation?
- As the protons pass through the F0 complex they cause the subunits to rotate by 1/3
- Each 1/3 turn causes a conformational change in the Beta subunit of F1 ATPase
What regulates oxidative phosphorylation?
ADP and ATP levels
How is oxidative phosphorylation regulated at rest?
The proton motive force is high but due to high ATP levels
–> minimal flow of protons through ATP synthase and low transfer of electrons
How is oxidative phosphorylation regulated during exercise?
ATP is consumed therefore ADP levels rise
–> proton movement through synthase discharging the proton motive force. Results in increase electron transfer to keep proton motive force
What are the two types of inhibitors of oxidative phosphorylation?
- Electron transport inhibitor
- Uncoupling agents
Give an example of an electron transport inhibitor and how it works
Cyanide, stops carriers from receiving electrons
Give an example of an uncoupling agent and how it works
2,4-Dinitrophenol, dissipates the proton gradient so have to work harder to make ATP
