Day 41 Flashcards
1
Q
Thermodynamics of Electron Transport
A
- Oxygen is the final electron receptor for both NADH and FADH2
- Remember that electron affinity increases with standard reduction potential
2
Q
ETC Sequence of Transport
A
- electrons passed from NADH and FADH2 to Complex 1 and Complex 2 respectively
- those electrons are then carried by Coenzyme Q (CoQ or ubiquinone) to Complex 3
- Complex 3 electrons are then carried by a peripheral membrane known as Cytochrome C to Complex 4
- Each complex catalyzes the redox reaction of electron transfer from one molecule to another - Complex 4 catalyzes electron transfer from cytochrome c to oxygen
- Transversing of electrons through Complex 1,3, and 4 power the synthesis of ATP
3
Q
Complex 1 Inhibitors
A
- Rotenone (plant toxin)
- Amytal )barbiturate
- they both block the electrons from transporting though
- ALLLL complex inhibitors block oxygen consumption because no use for final electron accepter
4
Q
Complex 3 Inhibitors
A
Antimycin A (antibiotic)
5
Q
Complex 4 Inhibitors
A
Cyanide
6
Q
More fun complex facts
A
- Each protein complex in the ETC have prosthetic groups capable of redox activity
- They all laterally mobile in the membrane and don’t form a higher stable structure ( not even present in equimolar amounts)
7
Q
Complex 1
A
Name: NADH-CoQ Oxidoreductase
- L-shaped with one arm in membrane other in matrix
- has flavin thing like FAD but no AMP moiety 6-7iron/sulfer clusters
8
Q
Complex 1 Coenzymes
A
1) Iron-Sulfur Cluster
- [2Fe-2S] and [4Fe-4s] but both have 4 cysteine sulfhydryls
- Cluster can undrgo one-electron redox reactions
2) FMN and CoQ
- together have three oxidation states (fully oxidized, semiquinone, fully reduced)
- Both can accept two or one electron
- FMN is tightly bound to proteins while CoQ has a hydrophobic tail and is soluble in lipid bilayer
9
Q
Electron Transport in Complex 1
A
- transit of electrons from NADH to CoQ is probably stepwise
- must involve reduction of each group as it binds electrons followed by oxidation as it passes the electrons along to the next group
- electrons can “jump” 14angstrums cuz quantum mechanics so redox centers don’t have to touch
- NADH can only give 2 electrons but cytochromes can only participate in 1 electron transfers…..so there are the two initial electron carriers FMN and CoQ to go from NADH trying to give 2 e to a 1e cytochrome
10
Q
Proton Translocation
A
- during electron transfer in Complex 1, 4 protons go into intermembrane space
- we don’t know how pumping works but pK values of side chains are probs altered
- Protons “hop” along a chain of hydrogen bonded groups unlike other ions.
- bacteriorhodopsin is light driven proton pump. When retinal changes, the protein conformation and pK change of a protein channel
11
Q
Complex 2
A
Name: Succinate-CoQ Oxidoreductase
- has enzyme succinate dehydrogenase (like the CAC with that FAD cofactor)
- has 3 iron-sulfur clusters and cytochrom b560 that comes with a heme group with reaction iron center
- Transport of electrons from succinate to CoQ DOES NOT MAKE ATP NOT SEQUENTIAL
12
Q
Complex 3
A
Name: CoQ-Cytochrom c Oxidoruductase
- passes electrons from reduced CoQ to cytochrome c
- has two b-type cytochromes, one cytochrome c1, and one iron-sulfur cluster that is coordinated by histidines know as Rieske Center
13
Q
The Q Cycle
A
- Electron transport and proton pumping in complex 3
- CoQH2 is an electron carrier that will permit two electrons to be carried in ordre to reduce two molecules of cytochrome c which is a one elecron carrier
- Occurs by a split in the electrons where one goes to cytochrome c and one goes to cytochrome b in a cyclic manner
- CoQH2 goes through a two cycle reoxidation where it froms a stable radical as an intermediate
- two independent binding sites. Qo–CoQH2 and Qi—CoQ’ and CoQ
14
Q
Cytochrome C
A
- electrons in cytochrome c1 are transferred to cytochrome c which is a peripheral membrane protein the the intermembrane space
- shuttles electrons from Com3 to Com4
- just like to other cytochromes, have redox-reactive iron coordinated in bound heme group
15
Q
Complex 4
A
Name: Cytochrome c Oxidase
- catalyzes the 1-electron oxidations of four consecutive reduced cytochrome c molecules and the 4 electron reduction of one O2 molecules
- 4 redox centers; cytochrome a, cytochrome a3, a copper atom known as CuB, and a pair of copper atoms knows as the CuA center
