Lecture 4 Flashcards
What are the names for Complex I?
NADH dehydrogenase and NADH:ubiquinone oxidoreductase
What is the overall reaction that occurs in Complex I?
NADH + Q + (H+) -> (NAD+) + QH2
What is Complex I’s main job?
To reduce ubiquinone to ubiquinol and to move 4 protons from the matrix to the IMS
Describe the electron transfer process in Complex I
NADH gives 2e- to the FMN transformer, which passes e- one at a time to Fe-S proteins. These Fe-S proteins then pass 2e- off one at a time to ubiquinone, which gets reduced to ubiquinol. The free energy from the reduction of Q to QH2 is harnessed to create a conformational change in the HL region, which allows 4 protons to flow from the matrix-side half channels to the IMS
What are other names for Complex III?
Cytochrome c or cytochrome bc1
Describe the electron transfer process in Complex III
QH2 takes one of two pathways:
- Passes off e- to Fe-S proteins, which then transfer e- to cytochrome c on the P-side
- Becomes radical Q-, which then becomes reduced by 2 protons from the matrix to reform QH2 on the N-side
Describe the cytochrome b monomers in Complex III
They form a homodimer that surrounds a cave in the inner membrane, where Q can move freely from the matrix to the IMS
What is the name of Complex IV?
Cytochrome oxidase
Describe the main job of Complex IV
It’s main job is to transfer electrons to oxygen
Describe the electron transfer process in Complex IV
Cytochrome c transfers e- to CuA in subunit I. CuA then transfers e- to heme A, which goes to the CuB-a3 binuclear complex in subunit II. O2 reduction to H2O happens at this binuclear complex.
How can ROS form at Complex IV?
Since oxygen is reduced at redox centers that carry only 1e- at a time, incompletely reduced O2 stays bound until completely converted to water. However, sometimes the incompletely reduced oxygen species escape as ROS
What is the name for Complex II?
Succinate dehydrogenase
What is the main job of Complex II?
Its main job is to oxidize succinate to fumarate in order to reduce Q to QH2
Describe the electron transfer process in Complex II
FADH2 donates 2e- to Fe-S centers (1 at a time I think). Fe-S proteins transfer electrons to Q, which reduces to QH2
Describe the electron transfer distance in Complex II
It’s long! The site of succinate oxidation is 40 angstroms away from the site of Q reduction. However, none of the individual e- transfer distances exceed 11 angstroms (remember the limit is 14 angstroms)
