lecture 32 Flashcards
What is the oxidative part of oxidative phosphorylation
Respiration-oxidation of NADH through a series of intermediates leading to ultimately O2
Where does respiration occur?
mitochondrial inner membrane
How is the energy used in oxidative phosphorylation?
the energy derived from these oxidative reactions is used to pump H+ ions from the mitochondrion matrix to the space between inner and outer mitochondrial membranes
Proton-motive force
the force produced from the electrochemical gradient that is generated from the H+ concentration difference across the inner membrane
Mitochondrial complex I-IV
- composed of multiple subunits
- multiple electron carriers within each of the complexes
- Complexes I, II, and III act as proton pumps (H+ translocases)
Translocases
- Mitochondrial complexes I, II, and III
- direct the movement of H+ against the concentration and electropotential gradient
- H+ is higher on the P side of the membrane and the net charge is positive on the P side
- work during the sequential oxidation/reduction of the electron carriers
Oxidative Phosphorylation
- Complexes I-IV contains the enzymes and coenzymes involved in reduction/oxidation reactions
- H+ are translocated to the transmembrane space, which creates the concentration and charge difference between the inter membrane and matrix spaces
- ATP synthase will use re-entering H+ ions as a source of energy for the conformational changes that occur during ATP synthesis
What reaction is used for complexes I, III, IV?
NADH + H+ + 1/2O2 -> NAD+ + H20
-movement of 10 H+ to the inter membrane space during passage of one e- through the complexes
What reaction is used for complexes II, III, IV?
Succinate + 1/2O -> Fumarate + H20
-movement of 6 H+ to the inter membrane space during passage of one e- through the complexes
Complex I
- is NADH/Q oxidoreductase (Or NADH dehydrogenase)
- overall reaction: NADH + H+ + Q-> NAD+ + QH2
- there are 9 intermediary carriers inside the NADH dehydrogenase Module
NADH Dehydrogenase Module
FMN and 8 Fe-S centers
QH2
FADH2
- lipid soluble
- diffuses through the membrane to complex III
Complex II
- is succinate dehydrogenase (only membrane bound molecule of the TCA Cycle)
- overall reaction: succinate + Q-> fumarate + QH2
- electron carriers: 1 FAD and 3 Fe-S centers before the 2 electrons are used for Q reduction
- No H+s are translocated during the oxidation/reduction reactions
Why are no H+s translocated in complex II
the reduction energy is nearly the same as QH2 so there is not net energy available for the reactions in complex II
What are the two dehydrogenase that carry out reactions similar to succinate dehydrogenase?
- acyl-CoA dehydrogenase (involved in B-oxidation of fatty acids)
- Glycerol 3-phosphate dehydrogenase (involved in oxidation of glycerol)-located in the outside of the inner mitochondrion membrane
Complex III
- is cytochrome bc1 complex
- 11 subunits total in the complex, but the three involved in the electron transport are cytochrome B subunit, ISP, and cytochrome c1 subunit
- Q cycle
Q cycle
1st stage-Binding of 1st QH2
2nd Stage-Binding of 2nd QH2
What is the net number of H+s translocated in the Q cycle?
4, because two H+s effectively come from the N side and 2 from QH2 (originating in the membrane), but they all count as H+p
1st stage of Q cycle: Binding of 1st QH2
-the 2 H+ are dissociated and translocated to the P side
The two electrons are divided into two paths:
- one goes through intermediaries to cyt c1
- the second goes through intermediaries to a ubiquinone to make a semiquinone radical
2nd Stage of Q cycle: Binding of 2nd QH2
-the 2 H+ are dissociated and translocated to the P side again
The two electrons are divided into two paths:
- one goes through the intermediaries again to a second cut c1
- the second goes through intermediaries again to reduce the semiquinone radical which with two H+s from the Nside forms QH2- which is released into the membrane lipid
Complex IV
- is cytochrome c oxidase
- 13 subunits in the eukaryotic version
- Subunits I, II, and III are the most important and are involved in e- flow and O2 reduction
- Subunit I contains two hemes and a Cu/Fe center
- four cyt c molecules bind and the electrons are transferred to the Cub center
- these transfers result in the splitting of the O2 molecule and the addition of H+ to form H20
- One H+ ion is translocated for each electron transferred from cyt c to O2
In what process does all of the energy in NADH is captured during respiration?
Proton-motive force
