Electron Transport Chain Flashcards
What is Complex I?
Is a large L shaped enzyme comprised of more than 40 subunits. It contains a FMN-containing flavoprotein, FE-S clusters and N-2.
It catalyses 2 simultaneous reactions:
- the exergonic transfer of a hydride ion and 2e- from NADH and a H+ from the matrix to ubiquinone (Q)
- the endergonic pumping of 4H+ per NADH from matrix to the IMS
The IMS becomes positively charged and the the matrix becomes negative
This process can be inhibited by a range of drugs (insecticide agents)
What is Coenzyme Q?
Is a lipophilic inner mitochondrial membrane dwelling mobile electron carrier that transfers electrons from Complex I and Complex II to Complex III
The oxidised form Q, is known as ubiquinone and the reduced form QH2 is referred to as ubiquinol
Coenzyme Q can also exist as a partly reduced form referred to as a semiquinone QH
What is Complex II?
Is also known as succinate dehydrogenase
Contains 4 protein subunits (A, B, C and D)
Electrons flow through this complex and it is not a hydrogen pump
What is Complex III?
Couples the transfer of electrons from ubiquinol to cytochrome c
Forms a dimer with each monomer comprised of 3 subunits (cytochrome b, Rieske Iron-Sulphur proteins, cytochrome c1)
Pumps 4H+ per NADH from the matrix to the IMS
Common drugs inhibit this complex
What is cytochrome c?
Is a small soluble protein that resides in the inner membrane space that accepts electrons from Complex III and donated them to Complex IV
Cytochrome c contains the prosthetic group Heme C with a central Fe3+ atom that becomes reduced to Fe2+ after accepting an electron from Complex III but returns to 2+ when the electron is donated to Complex IV
What is Complex IV?
Accepts electrons from cytochrome c and donates them to O2 which becomes reduced to H2O
Comprised of 4 subunits
Pumps 2H+ per NADH -> 4H+ per O2
ATP synthase
Uses the H+ gradient formed via the pumping of protons by Complexes I, III and IV to drive the unfavourable synthesis of ATP from ADP + Pi
Is comprised of a F0 (stalk) and a F1 (head) component
F0 spans the inner mitochondrial membrane and is comprised of an a subunit, 2b2 subunits and 10c subunits in yeast or 8c in mammals
F1 is located on the matrix side of the inner membrane and is comprised of 9 subunits
ATP synthesis results from the rotational catalysis mechanism
What is the phosphate translocase?
Phosphate renters the mitochondrial matrix with H+, by an electroneural symport mechanism - Pi is driven by and uses up the pH gradient
What is adenine nucleoside translocase?
Is an antiporter that catalyses the exchange of ADP for ATP across the IMS
What is oxidative phosphorylation and the chemiosmotic model?
Oxidative phosphorylation is the process of transforming redox energy under aerobic conditions during glycolysis and the citric acid cycle into chemical energy in the form of ATP
- Redox energy is converted to an electrochemical gradient which drives the unfavourable formation of ATP
What are the major steps of this?
- Transfer of electrons from NADH to complex I and/or transfer of electrons from FADH2 to complex II
- Flow of electrons through the inner mitochondrial membrane complexes and mobile electron transporters of the electron transport chain
- Pumping of protons from the matrix to the IMS using the proton pumps of Complex I, III and IV as electrons flow through these complexes
- Flow of protons from the IMS through the F0 component of ATP synthase (F0F1 ATPase) back into the matrix resulting in the rotation of the F0 component and gamma subunit of F1 and the synthesis of ATP from ADP and Pi by the F1 component
What rotates ATP synthase?
- The F1 component has 3 nonequivalent adenine nucleotide-binding sites, one for each a/b pair
- One of these sites is in the b-ATP conformation, which binds ATP tightly
- A second is in the b-ADP conformation which binds ADP + Pi
- A third is in the b-empty conformation
- The proton motive force causes rotation of the gamma subunit as H+ is pumped through the F0 component
