Unit 6 - Electron Transport by Respiratory Chain Flashcards
where is the respiratory chain located? what are its components?
enzymes are embedded in the inner mitochondrial membrane
- complex I - NADH dehydrogenase
- Q - quinone (dissolved in liquid phase)
- complex III - bc1 complex
- cytochrome c - bound to IMM in intermembrane space
- complex IV - cytochrome oxidase
what are the advantages of a membrane-bound respiratory chain?
- not limited by the rate of diffusion
- no mobile carrier needed
- E stored in reduced fuels are converted to E stored in electrochemical gradient (needs 2 compartments provided by membrane)
what are the 5 REDOX centers of respiratory chain?
- flavins
- Fe-S centers
- ubiquinone
- hemes
- copper centers
what are flavins? and examples?
2-electron donor/acceptor + 2H+ via 1,4 addition
- includes FMN (flavin mononucleotide; oxidized), FMNH2 (reduced), and FAD (flavin adenine dinucleotide; oxidized)
- -FAD has adenine bound, so needs specific binding site
what REDOX center does NADH dehydrogenase have?
tightly bound FMN
what REDOX center does succinate dehydrogenase have?
covalently bound FAD
what REDOX center does FA-CoA dehydrogenase have?
FAD
what REDOX center does glycerol phosphate dehydrogenase have?
FAD
what are Fe-S centers? examples?
accept electrons from flavins and Q
- no matter how many Fe, only accept/donate 1 electron
- Fe2S2 of complex III
- -2 Fe+++ + e- –> 2 Fe2.5+
- Fe4S4 of succinate dehydrogenase
- -2 Fe+++ + 2 Fe+++ e- –> Fe+++ + 3 Fe++
- -3 Fe+++ + Fe++ + e- –> 2 Fe+++ + 2 Fe++
what happens if Fe-S centers are acidified?
makes H2S gas (like what happens in old eggs)
what is ubiquinone? (also Q, Ub-Q, CoQ, etc.)
-why is it unique?
two electron donor/acceptor + 2H+
- 1,6 addition
- 10 isoprenoid chains in mammals
- very hydrophobic
- 10-fold excess over other components
- function as electron buffer
- unlike the other REDOX centers, it’s not a prosthetic group
- unique b/c excess mobile electron carrier between early dehydrogenases and later part of respiratory chain
what is heme as a REDOX center?
one-electron donor/acceptor
- Fe+++ + e- –> Fe++
- covalently attached to 2 cysteine side chains in cytochromes c and c1
- -Fe atom coordinates to met 80 and his 18 side chains
how is the structure of cytochrome:c, cytochrome b, and heme c?
- cytochrome c has highly conserved structure
- cytochrome b hemes are 1 protein with 2 cytochrome complexes bound to same IMM walls
- heme C has thioester linkages to a protein
what are copper centers as REDOX centers?
one electron donor/acceptors in cytochrome oxidase (complex IV)
- CC A: has 2 Cu
- -2 Cu++ + e- Cu++ + Cu+
- CC B: along with heme of cyt a3 forms O2 binding site at end of respiratory chain
how are electron carriers arranged along respiratory chain?
increasing affinity for electrons (Eo’)
- important for efficiency of extracting useful energy
- NAD –> Q –> bc1 complex –> cytochrome c –> cytochrome a
- when electron passes thru large Eo’ drop, it’s passing from REDOX center of low affinity to greater affinity
- -stabilization of electron is an exergonic process that could be coupled to endergonic generation of electrochemical gradient
what is the only heme group in the respiratory chain that binds O2?
cytochrome a3 of cytochrome oxidase
-it’s the last thing to be reduced, thus maintaining ferric Fe
what are the components of cytochrome oxidase? why are these components necessary?
cytochrome c –> Cu A –> heme A –> heme a3 (bound to O2 and Cu B)
-participation of 2 Cu centers and 2 heme irons in cytochrome oxidase are required to rapidly deliver 4 electrons to O2, and avoid production of H2O2 and superoxides
ATP synthase (FoF1) structure
- F1 has 3 catalytic sites for ATP synthesis (juts into matrix)
- Fo is hydrophobic complex that traverses membrane and carries H+ from one site to another (sits on membrane)
- connected by central stalk (rotor) and external stalk (stator)
overall reaction for oxidative phosphorylation
-how is this related to respiratory control?
NADH + H+ + 1/2 O2 + 3 ADP + 3 Pi –> NAD+ + 3 ATP + 4 H2O
- IOW: 1 NADH ~ 3 ATP (actually about 2.7)
- obligatory linkage of endergonic ATP synthesis to exergonic REDOX RXNs
respiratory control and what causes it
electrochemical gradient functions as a common intermediate linking oxidation to phosphorylation
- O2 consumption is coupled to ATP synthesis
- rate of respiration is controlled by availability of ADP
what is the P/O ratio?
ADP consumed / O consumed = ATP formed per pair of electrons from substate to O2
what is the overall job of the respiratory chain?
break up the 52 kcal/mol available from flow of 2 electrons from NADH to O2 into 3 equal amounts, used to drive formation of ATP
