B L2 Flashcards
Describe the structure of the mitochondria. Permeability of its membranes. Contents.
Where do glycolysis, TCA cycle and the ETC occur?
Glycolysis –> Cytoplasm of mitochondria
TCA –> matrix of mito.
ETC –> inner membrane of mito.
What are the requirements for the membrane for ETC/ chemiosmotic energy coupling ?
The proton gradient needed for ATP synthesis can be stably established across a membrane that is impermeable to ions.
– plasma membrane in bacteria
– inner membrane in mitochondria
– thylakoid membrane in chloroplasts
* The membrane must contain proteins that couple the “downhill” flow of electrons in the electron-transfer chain with the “uphill” flow of protons across the membrane.
* The membrane must contain a protein that couples the “downhill” flow of protons to the phosphorylation of ADP.
What are the main reduced fuels for the cell?
Carbs, lipids, amino acids
Which membrane proteins pump protons in the ETC? What is the proton gradient set up by them? What is the chemical and electric potential established as a result of this proton gradient?
- Complex I, III and IV
- Protons pumped from matrix into intermembrane space thus higher conc. of protons in the intermemb space than in matrix
- Chemical: high conc of protons in intermemb. space thus lower pH (acidic) and higher pH (alkaline) in matrix
- Electrical: high conc of protons in intermemb. space thus more +ve charge than in matrix.
How many electrons can a cytochrome carry?
Which protein complexes do they move between?
- one electron carrier
- Move btwn protein complex III and IV
What drives ATP synthesis in the ETC?
The proton motive force set up by the proton gradient establishes a chemical and electric potential.
This electrochemical potential causes the ATP synthase (complex V) to drive production of ATP.
How many electrons can a Fe-S cluster carry?
Which protein complexes are they present in? Where does the sulfur come from?
one electron carrier
- Present in complex I, II and III
- Cysteine residues
How many sulfur atoms will be present in an Fe-S cluster in relation to the iron atoms?
They will be equal in number
same number of Fe as S atoms
What type of macromolecule is ubiquinone?
It is a lipid
NOT A PROTEIN!!
What is the reduced form of ubiquinone? How many electrons and protons does it accept/carry?
Ubiquinol
When ubiquinone accepts 2 electrons and 2 protons it changes into ubiquinol – which is an alcohol and can freely diffuse in the membrane allowing it to transport electrons
What is ubiquinol also known as? What is its function? Which protein complexes is it linked to in the ETC?
Coenzyme Q
Ubiquinone is reduced to form coenzyme Q (gains 2 e- and 2 H+)
It thus transports electrons from complexes I, II and III (From III to IV it’s cytochrome c)
What is the name of complex I? Which cofactor binds to it?
NADH ubiquinone oxidoreductase
NADH binds to this protein complex at its binding site on the matrix side and gets oxidised – thus gives up 2 e-
Which prosthetic group accepts the electrons from NADH that binds to complex I? How many electrons?
NADH gets oxidised and gives up 2 e- which are accepted by the prosthetic group – FMN (Flavin mononucleotide)
Briefly explain what happens at Complex I (protons pumped? Prosthetic groups involved? how electrons are transferred? etc.)
What is the name of Complex II? What does it accept its electrons from? How many electrons?
Succinate dehydrogenase
It accepts its electrons from FADH2 (succinate - a product of TCA cycle - passes on 2 e- to FAD which becomes FADH2 - FADH2 then gives the e- that travel along Fe-S clusters)
It accepts 2 electrons from FADH2
How many protons does complex II pump?
None - it is not involved in the pumping of protons
What are the 2 roles of complex II?
- Converts succinate to fumarate
- Captures and donates e- in the ETC.
What is the final acceptor of electrons in complex II?
Coenzyme Q (ubiquinol –> ubiquinone becomes ubiquinol on accepting electrons)
Briefly explain what happens at Complex II (protons pumped? Prosthetic groups involved? how electrons are transferred? etc.)
What is the name of complex III? What does it accept its electrons from? how many?
Cytochrome c oxidoreductase
From coenzyme Q (QH2)
It uses 2 electrons from from QH2 to reduce cytochrome c (so it can act as an electron carrier)
What is the final acceptor of electrons in complex III? How many electrons does it carry?
Cytochrome c
It carries 1 electron
How are cytochrome c and coenzyme Q different in their movement and electron carrying capacity?
Cytochrome c –
> Moves through the intermembrane space
> Carries one electron
> Its a protein
Coenzyme Q (QH2) –
> moves through the inner membrane itself
> carries 2 electrons
> Its a lipid
Briefly explain what happens at Complex III (protons pumped? Prosthetic groups involved? how electrons are transferred? etc.)
