Metabolism 5- Oxidative Phosphorylation Flashcards
Where does oxidative phosphorylation take place
In the cristae ( folds of the inner membrane)
What is the advantage of the cristae being folded
It increases the surface area in which oxidative phosphorylation can take place.
What is the evidence that supports the endosymbiosis theory.
Mitochondria can only arise from pre-existing mitochondria.
They possess their own genome which resembles that of prokaryotes- single, circular loop of DNA with no associated histones
They have their own ribosomes, which are similar to prokaryotic ribosomes.
The first amino acid of mitochondrial transcript is formylated methionine residue (fMet) - same in bacteria- not methionine (Met) as in eukaryotes.
A number of antibiotics (Streptomycin) that act by blocking bacterial protein synthesis also block protein synthesis within the mitochondria. They do not interfere with protein synthesis in the cytoplasm of the eukaryotes.
How many genes does mtDNA encode for
37 genes, and their can be several copies within the cell.
Where is mtDNA inherited from
The ovum, and hence it is inherited from the mother, all mutations are passed on to the maternal offspring.
Describe the re-oxidisation reactions of NADH and FADH2
NADH + H+ + 0.5O2 — NAD+ + H20
FADH2 + 0.5 O2 — FADH2 + H2O
What are the two steps of the chemiosmotic model of oxidative phosphorylation
The translocation of protons from within the matrix of the mitochondria. This is controlled by the ETC.
The pumped protons are allowed back into the mitochondria through a specific channel which is coupled to an enzyme which can synthesise ATP.
Describe the role of the NADH dehydrogenase complex in the ETC
Accepts electrons from NADH. The electrons are extracted in the form of a hydride ion, which is then converted into a proton and two high energy electrons- a reaction catalysed by the NADH dehydrogenase complex. The proton is pumped into the intermembrane space
Describe the other events in the electron transport chain
The electrons from the NADH dehydrogenase complex are passed to a carrier protein ( ubiquinone) which transfers the electrons to the cytochrome c reductase complex, proton pumped into intermembrane space. Electrons are then transferred to cytochrome c (carrier protein) which transfers the electrons to the cytochrome c oxidase complex, which pumps protons into the intermembrane space.
Why is the transfer of electrons energetically favourable
The electrons are passed from electron carriers with weaker electron affinities to those with stronger electron affinities, until they combine with a molecule of O2 to form water. Hence electrons lose energy as they pass through the ETC.
Where else can ubiquinone accept electrons from
From the re-oxidation of FADH2, produced from the action of succinate dehydrogenase.
Define redox
Reactions which involve electron transfer - involves a reduced substrate and an oxidised substrate.
What is a redox couple
A substrate that can exist in both oxidised and reduced forms.
What does a negative E’O value imply
The redox couple has a tendency to accept electrons and so has more oxidising power than hydrogen.
What does a positive E’O value imply
The redox couple has a tendency to donate electrons, and so has more reducing power than hydrogen.
What are the two consequences of proton pumping.
pH gradient created across the inner membrane- pH in matrix 7.9- pH in intermembrane space- 7.9
Voltage gradient created- matrix becomes negative- side facing the intermembrane space becomes positive.
How do the pH gradient and membrane potential work together
They create a steep electrochemical proton gradient that makes it energetically very favourable for H+ ions to flow back into the mitochondrial matrix. The membrane potential contributes significantly to the proton motive force which pulls the H+ back across the membrane- the greater the membrane potential- the more energy stored in the proton gradient.
What would happen if protons were simply allowed to flow back into the matrix
The energy would be lost as heat.
Describe the structure of ATP synthase
Membrane bound part (F0)- H+ carrier
F1 head-part of protein where phosphorylation of ADP takes place.
Stalk connects F0 to F1.
Describe how ATP synthase functions
The passage of protons through the carrier causes the carrier and its stalk to spin rapidly, like a tiny motor. As the stalk rotates it rubs against the proteins in the stationary head, altering their conformation and prompting the production of ATP. A mechanical deformation gets converted into the chemical bond energy of ATP.
How can ATP synthase work in reverse
Energy can be used from ATP hydrolysis to pump protons uphill against their electrochemical gradient, functioning like the H+ pumps. Whether ATP synthase makes ATP or consumes it depends on the magnitudes of the electrochemical proton gradient/
Delta G needs to be large enough to drive ATP production.
Consequences of accepting electrons from FADH2
One less proton pumped into intermembrane space, less ATP produced.
How can the concentration of oxygen in solution be determined
Oxygen electrode- Pt cathode and AG anode underneath a Teflon membrane, which is permeable to O2.
Describe how the oxygen electrode works
Oxygen is reduced to water at the Pt cathode
02 + 4H+ + 4e- — 2H20
Circuit is completed at the silver anode which is slowly oxidised to AgCl by the KCl electrolyte
4Ag+ + 4Cl- — AgCl + 4e-
The resulting current is directly proportional to the oxygen concentration in the sample chamber.
