Lecture 18 - Electron transport 2 Flashcards
(22 cards)
Slide 30 - 38
Describe the mitochondrial electron transport system
Electrons from NADH enter the electron transport system at complex I, then flow to coenzyme Q, complex III, and complex IV. A total of 10 H+ are concomitantly translocated.
Electron pairs are derived from FADH2 oxidation at complex II (succinatedehydrogenase), from ETF-Q oxidoreductase of the fatty acid oxidation pathway, or from mitochondrial glycerol-3-phosphate dehydrogenase, which is part of the glycerol-3-phosphate shuttle. A total of 6 H+ are concomitantly translocated when electrons are derived fromFADH2.
What is Complex I called in the METS and what does it do
NADH-Ubiquinone Oxidoreductase
NADH oxidation coupled to FMN reduction
At least 7 Fe-S centres carrying 1e- at a time
Translocates 4 H+ into intermembrane space
How does complex I work in METS
NADH transfers 2 e- to FMN
2e- transferred from carrier to carrier
2e- + 2H+ bind Q, forming QH2
What does rotenone do
blocks electron transport in complex I, prevents reduce reactions between 2 Fe-S centres
What is FMN
Flavin Mononucleotide
What is the job of FMN in OP
FMN accepts one electron
Reduction by one electron forms a semiquinone intermediate
Reduction by a second electron leads to the fully reduced species (FMNH2)
Isoalloxazine ring identical to that of FAD
How are the Fe-S clusters composed and what are they coordinated by
2 Fe-2 S clusters or 4 Fe-4 S cluster
coordinated through cysteine residues in the protein subunits
How many electrons does each Fe-S cluster transfer to the next
1
What is the redox potential in the Fe-S clusters
-0.5V to +0.4V depending on protein microenvironment
Sequence of Fe-S clusters in complex I will have increasing redox potentials
What is Coenzyme Q also known as
Ubiquinone/ Ubiquinol
What are the key roles of CoQ
Mobile, lipid-soluble e- carrier - transports electrons in membrane from complex I to III
- Entry point into electron transport system for e- pairs from citric acid cycle, fatty acid oxidation, and glycerol-3-phosphate dehydrogenase
- Converts 2e- transport system in complexes I and II to 1e- system in complex III, which then passes electrons one at a time to cytochrome c
What is complex II also called
Succinate Dehydrogenase
What does Complex II do
Direct physical link to CA cycle
Oxidises succinate to fumarate, coupled with FAD-FADH2
Electron pair then used to reduce Q via Fe-S and a haem
What is complex III also called
Ubiquinone-Cytochrome C Oxidoreductase
How many binding sites does complex III have
2 Q bonding sites - Qp and QN
along with several prosthetic groups which act as electron carriers
What does complex III do
Reduces Cyt c while translocating 4H+
Dimeric complex - 2x11 subunits
CoQ uses Q cycle to convert 2e- processes into two 1e- transfers
What does a type a haem have
Hydrophobic tail
What does a type b haem have
standard
What does a type c haem have
Protein link between 2 cysteine residues
What is Complex IV also called
Cytochrome c oxidase
What does complex IV do
Cyt C oxidation
then electron transfer through one monomer of the homodimer, culminating in O2 reduction to form H2O
Four H+ are involved in the complex IV reactions:
2 H+ translocated into intermembrane space 2 H+ used to form H2O