Oxidative Phosphorylation In Health + Disease Wk4 Flashcards
Oxidative phosphorylation overview
-electrons transferred through four protein complexes - to oxygen to form water
-transfer of electrons drive proton pumps establishing a proton gradient
-proton gradient drives ATP-synthase to generate ATP from ADP
Glycolysis generates Pyruvate
Pyruvate feeds into TCA/Krebs cycle
NADH and FADH2 generation feeds into electron transport chain
Electron flow through complexes is achieved via Fe-S or Haem groups
Electron carriers in complex proteins
Fe based EC are found in protein complexes + cytochromes
Fe-S (lower affinity) predominate in early complexes
Haem groups (higher affinity) predominate in later complexes
Even if Fe-S centres have multiple Fe atoms, each Fe-S will only carry 1 electron at a time
Mobile electron carriers - Ubiquinone
-Coenzyme Q
-hydrophobic quinone molecule, move through lipid bilayer
-carries electrons from complexes | and || to |||
MEC - cytochrome c
Carries electrons from complex ||| to |V
-fe groups in Haem c group
-highly conserved through evolution
-water soluble, loosely associated with outer side of IMM
Acts as anti-oxidant
Complex I of ETC - NADH-ubiquinone oxidoreductase
-L-shaped membrane bound protein
-peripheral arm responsible for electron transfer
Membrane arm responsible for proton pumping
14 core subunits (7 peripheral, 7 membrane) 30 accessory subunits
I structure-function
-electrons donated from NADH to FMN
-^ transferred through 7 Fe-S clusters
-final Fe-S donates to ubiquinone
-negative charge on ubiquinone drives conformational changes in the E-channel
Moves through ‘open’ and ‘closed’ states driving proton transport through the membrane region
Complex II - succinct dehydrogenase
Involved in Krebs cycle + ETC
-catalyses conversion of Succinate to Fumarate in Krebs
- passes electrons to ubiquinone for transfer to complex III
II - electron flow
-four subunit protein complex
-succinate to Fumarate conversion transfers electrons to FAD to generate FADH2
-electrons are passed through 3 Fe-S groups to ubiquinone
Complex III - Cytochrome bc1 oxidoreductase
-11 subunits : 3 respiratory subunits, 2 core proteins + 6 low-molecular weight proteins
-initiates proton flow via the Q cycle
III - the Q cycle - step 1
Cytochrome b binds a ubiquinol and a ubiquinone
Ubiquinol releases electron to Fe-S and L-Haem, releasing 2 protons
Fe-S transfers electron to cytochrome C1. Cytochrome C1 passes electron to Cytochrome C
L-Haem transfers electron to H-Haem. H-Haem passes electron to ubiquinone generating semiquinone
The first ubiquinol (now oxidised to ubiquinone) is released
Complex III – the Q cycle
Step 2
A second ubiquinol is bound
Ubiquinol releases electron to Fe-S and L-Haem, releasing 2 protons
Fe-S transfers electron to cytochrome C1. Cytochrome C1 passes electron to Cytochrome C
L-Haem transfers electron to H-Haem. H-Haem passes electron to semiquinone along with 2 protons from the matrix forming ubiquinol
The ubiquinone and ubiquinol are released
Complex IV - cytochrome c oxidase
-14 subunits
- 22 heme groups, 1 cytochrome a, 1 cytochrome a3, 2 copper centres
Complex IV – electron flow
- electrons passed from reduced cytochrome C via Cu and Fe centres to a binuclear centre
- ^ catalyses oxygen reduction to form water, with protons from matrix side
-Electron transfer linked proton transport shuttles protons to the intermembrane space
Chemi osmosis - linking H+ gradient to ATP production
^ describes movement of ions across a membrane following electrochemical gradient
- peter D Mitchell hypothesised that in mitochondria this movement of ions was utilised to drive the synthesis of ATP
-not accepted at the time,
-chemiosmosis essential in photosynthesis
Complex V - ATP synthase
Comprised of membrane bound F0 section + a Cytoplasmic F1 section
- F0 formed of ring of C subunits, an a subunit through protons can move + a b subunit which connects to F1
-F1 is formed of a central Y subunit which connects to the F0 c ring, + ring of alternating a and b subunits
Complex V – protons drive rotation in F0
Proton mov through F0 drives rotation of the g subunit which drives ATP formation in F1
Protons enter a subunit then C subunit driving rotation of c ring
-following rotation, protons are released on matrix side through a subunit
-rotation of c ring drives rotation of g subunit connecting to F1
Complex V – g rotation drives ATP synthesis
In F1, g rotates against static a and b
- g rotation drives conformational changes at three actives sites in a cycle of
1. Binding of ADP and Pi (loose state)
2. Confirmation change brings ADP and Pi together = ATP (tight state)
3. Release of ATP (open state)
The P:O ratio
Molecular ratio of amount of |p incorporated into ATP per oxygen
- for NADH ~2.5
-FADH2 `1.5
Uncouplers
Uncoupling uncouples proton electron transport and phosphorylation reactions
Inhibit ATP synthesis without affecting respiratory chain and ATP synthase (H(+)-ATPase)
2,4-dinitrophenol (DNP)
-used as diet pills + pesticide 1933 1998
-functions as protonophore
-hydrophobic, diffuses across membrane
-carries protons
-removes proton gradient
-ETC still functions but without proton gradient ATP cannot be produced via complex V
-energy is used for ETC but no ATP payout
= metabolic rate increased
Uncoupling proteins
Proton transporter proteins
- localised in mitochondrial membrane
-disrupt proton gradient, uncoupling ATP synthesis from electron flow
-UCP1 thermogenin
Expressed in brown fat, controlled by GPCR
Regulated heat generation during hibernation
-UCP2 and UCP3
Expressed in tisssues incl. pancreas + hippocampus
Regulates negative feedback loops in mitochondria or ROS production
Inhibitors of specific ETC components
Drugs + toxins can disrupt specific components of ECT
Rotenone
Acts on complex I
-inhibits transfer of electrons from Fe-S centres to ubiquinone
-unable to pass electrons to ubiquinone leading to backup of electrons in matrix
-can cause mitochondrial damage due to ROS production
-used as pesticide
- can be used against invasive fish species
Antimycin A
Blocks Qi site of complex III = blocking ubiquinol oxidation
