where does terminal respiration occur?
in the mitochondria, the only site of oxidative phosphorylation in eukaryotes
why is the mitochondria a good site for oxidative phosphorylation to occur?
Allows the coupling of the oxidation of carbon fuels to ATP synthesis
Utilises proton gradients to produce ATP (and lots of it)
the majority of NADH and FADH2 is formed in the matrix (from TCA and β-oxidation of fatty acids)
some NADH is formed in the cytoplasm from glycolysis. how is this moved to the mitochondria for use?
A shuttle is used to move reducing equivalents across the mitochondrial membrane
Cytoplasmic NADH cannot cross the membrane, but FADH2 can pass it’s e-’s on to the electron transport chain within the mitochondria
This process is termed the GLYCEROL PHOSPHATE SHUTTLE
describe the mechanism of the glycerol phosphate shuttle
- The NADH is unable to cross the membranes of the mitochondria, but G-3-P can, passing it’s e-’s to FADH2
- Oxidation of FADH2 in the electron transport chain generates, per mol, less ATP than oxidation of NADH
- Thus, an energetic ‘price’ is paid for using cytosolic reduced co-substrates in terminal respiration
what is complex 1 of the electron transport chain called and what is its’ function?
NADH-1 oxidoreductase
- Oxidises NADH and passes the high-energy e-’s to ubiquinone to give ubiquinol (QH2)
- Pumps H+ ions into the intermembrane space
what is complex 2 of the electron transport chain called and what is its’ function?
Succinate-Q reductase
-Oxidises FADH2 and like complex I passes high-energy e-’s to ubiquinone, which becomes ubiquinol (QH2)
what is ubiquinone (Q) and what are its’ alternate names?
Dietary supplement believed to reduce free radicals and thus act as an antioxidant
- Called Q10 in mitochondria (as it has 10 isoprene repeats)
- CoenzymeQ10 is its’ other name
what is complex 3 of the electron transport chain called and what is its’ function?
Q- cytochrome c oxidoreductase
- Takes the e-’s from ubiquinol (QH2) and passes them to cytochrome c
- 1 QH2 is oxidised to yield two reduced cytochrome c molecules
- Pumps protons into the intermembrane space
what is complex 4 of the electron transport chain called and what is its’ function?
Cytochrome c oxidase
- Takes the e-’s from cytochrome c and passes them to molecular O2
- e-’s channelled through Fe-Cu centre
- Pumps protons into the intermembrane space
how is energy conserved in e- flow through the chain?
- Energy is conserved from the breakdown of food molecules and ultimately leads to the oxidation of NADH, FADH2, ubiquinone and cytochrome c
- Energy is further conserved through the setting up of a proton gradient across the inner mitochondrial membrane
how is the energy stored up in the H+ gradient used? (2)
- the electron motive force (proton notice force)
2. a molecular turbine has evolved to harness the energy in the proton gradient = ATP synthase
what is chemiosmosis with regard to the electron transport chain?
As e-’s pass through the complexes of the transport chain protons move from the matrix to the outside of the inner mitochondrial membrane
what is proton motive force with regard to the electron transport chain?
When the protons moved to the outside of the inner mitochondria membrane via chemiosmosis are ‘allowed’ to flow back down their gradient, they release energy to do work
how is ATP synthesised in the ETC?
Protons eventually flow down their concentration gradient, back into the matrix of the mitochondria
at the specific sites where this occurs, there is a large multi-unit protein called ATP synthase/ATPase, which has a mechanism that allows protons to pass through
As they flow through ATPase, the energy stored in the gradient is used to convert ADP + Pi to ATP
ATP then takes this potential energy to do work in the cells of the body
what are the 2 parts of ATP synthase?
F0- the membrane bound proton conducting unit (has 10 subunits)
F1- protrudes into the mitochondria metric and acts as a catalyst for ATP synthesis
describe the action of an ATPase
- ADP + Pi enters β subunit
- ADP → ATP
- Rotation of F0 cylinder and γ shaft forces conformational changes in the β subunits of F1
- Conformational changes catalyse the ADP → ATP conversion and release ATP
describe the ending change mechanism of an ATPase
Protons move from positive side of membrane (H+ P) to the negative side (H+ N)
Sequential conformational changes of β subunit:
- β subunit that binds ADP + Pi
- β subunit that binds ATP
- β subunit that doesn’t bind ATP
electron transport is said to be coupled to ATP synthesis. what does this mean if they were to become uncoupled?
- If the inner mitochondrial membrane becomes permeable to protons, the proton gradient cannot be generated
- If this happens the electron transport can still occur, with O2 being reduced to H2O, but no ATP is made
- The two processes are now uncoupled
- The energy released from e-’s passing along the terminal respiration system does not make ATP, and is released as heat e.g. malignant hyperthermia
malignant hyperthermia is a disease caused by ‘leaky’ mitochondrial membranes that uncouple electron transport and ATP synthase. how does this usually come about?
when susceptible people are exposed to an anaesthetic called halothane, it is believed to make the inner mitochondrial membranes in muscle somehow leaky.
muscle cells will usually become irreversibly damaged from the excessive heat build up.
uncoupling is not always a bad thing. give an example of intentional uncoupling.
- Brown fat in newborn infants
- Brown fat cells have lots of mitochondria (iron in ETC)
- If a baby becomes cold, norepinephrine triggers the opening of a channel in a protein called thermogenin
- Thermogenin sits on the inner mitochondrial membrane of brown fat cells
