Ox Phos - Mitochondria Flashcards
(20 cards)
Where does oxidative phosphorylation take place?
In the inner mitochondrial membrane
- matrix above and inner membrane space underneath
What is the function of the mitochondrial respiratory chain?
- to pump H+ across the inner mitochondrial membrane and generate a proton electrochemical gradient (Δp)
- a substantial Δp is generated
- enough Δp to drive H+ back across the membrane through ATP synthase, causing production of ATP
How many protons are picked up from the matrix for every 2 electrons?
every 2 electrons = 10 protons
What happens at complex I?
- NADH diffuses through the matrix until it encounters Complex I
- Oxidation of NADH by FMN.
- Semiquinone state of FMN enables a change from 2e- to 1e- transfers
- NADH -> NAD+ + H+ - Transfer of e- one at a time, down a “wire” consisting of ~7 FeS clusters
- The e- down the cluster reduces Quinone
- made possible by semiquinone intermediate
- 2H+ + UQ -> UQH2 - Fully reduced UQH2 dissociates from complex I, diffusing within the hydrophobic fatty acid side-chains of the phospholipid
- creates a UQ pool
- eventually will encounter Complex III - E- transfer through complex I is coupled to translocation of 4H+ across the inner mitochondrial membrane, contributing to the Δp
What is the structure of complex I?
4 subunits
Another subunit potruding onto the matrix side which has Flavin (FMN) and also where NADH binds and UQ gets reduced
Long alpha helix
- repeating conformational changes in the first unit so that other protons can be diffused through easier
- positive induction
What happens at complex III/ during the Q cycle?
- Reduced quinone (UQH2) arrive at quinone binding site
- Can give up one e at a time or both at once
- 1 e transfers to iron sulfur cluster
- Then goes to a cytochrome called Heme c1 and then to cytochrome c (inside the mitochondrial space)
- 2nd e- transfers onto heme bl
- Onto bh and then onto another Quinone
- Reducing the Q (leaving radical, Q dot)
Overall reduced cytochrome c & one reduced quinone close to matrix space - A second UQH2 attaches to the quinone binding site
- One e follows 1st path again & reduces cytochrome c
- Another e follows the other pathway and reduces the other quinone near the matrix
Overall reducing one Quinone, 2 cytochrome c’s and pulling 2 protons
What is the structure of complex III?
multi-polypeptide transmembrane protein
- 3 Haems
- 2 Iron sulphurs
- 2UQ-binding sites per monomer
How many cyt c’s are reduced per UQH2 in complex III?
2
Why do the two electrons go to 2 different pathways when being donated by UQH2 in Complex III?
FeS behaves like a pendulum (swinging backwards and forwards) - picking up the first electron and then swinging to the second position
- As the e is being dropped off at the second position (cytochrome c1) the distance is larger and less competitive than the alternate pathway for the second e and so it goes on the alternate route
Why does the 1st electron go through that specific pathway in the Q cycle?
1st e goes through the pathway due to:
- Distance of FeS, Cytochrome c1 and cytochrome c are shorter
- Mid-point potentials give the blue path a more competitive rate
Why does the 2nd electron go through the alternate pathway in the Q cycle?
2nd e goes through alternate path due to:
- going from a lower Em to a higher Em
What is the other name for complex III?
cytochrome bc1
What is the other name for complex IV?
cytochrome aa3
What happens at complex IV?
- 4 cyt c delivering 4 e-
complex has 2 copper atoms - bound to polypeptides in a binuclear copper site - E’s arrive to copper one at a time
- Hop to Haem a3
- Then transfers onto CuB/Haema3 centre
- O2 binds next to the complex and is reduced to O2 2-
- Further reduced to 2H2O (by two more cyt c and 4H+ from matrix)
- Coupled to the O2 reduction, 2H+ are pumped across membrane per 1/2O2
Where does Oxygen bind in complex IV?
Between Haem a3 & CuB
What is the overall Oxidative Phosphorylation reaction?
2Cytc (red) + 1/2O2 + 4H+ -> 2Cytc (ox) +H2O + 2H+
What is complex II used for?
- links Krebs cycle with Ox.Phos - alternate pathway into the ETC
- starts at a lower point in energy
- provides an extra source of electrons into the respiratory chain
- not a proton pump
How are electrons introduced to the ETC from complex II?
mitochondrial succinate DH catalyses the step of turning succinate to fumarate
- the 2e- go down a series of FeS clusters
- can reduce Quinone
What is the structure of Complex II?
- flavin binding site
- FeS clusters
- Quinone Binding site in the membrane
How can a bacteria respire on fumarate?
similar to complex II but operates in opposite way
- Electrons are going up the chain to fumarate
- Neighbour proteins produce the e’s that feed up to fumarate
Proton gradient is still made
