Cell integrity Flashcards
What is substrate level phosphorylation?
Formation of ATP or ATP equivalent such as GTP
How is the bulk of ATP formed?
By oxidative phosphorylation
Where does oxidative phosphorylation occur?
Inner membrane of mitochondria
Many folds of cristae increase S.A. where oxidative phosphorylation takes place
What happens to NADH and FADH2?
Reoxidised by molecular oxygen:
NADH + H+ + 1/2 O2 -> NAD+ +H2O
FADH + H+ + 1/2 O2 -> FAD + H2O
What is the free energy (delta G) of the reaction of NADH and FADH2?
-223 and -170 KJ/mol respectively
What are the different membrane proteins in the electron transport chain?
Complex I (aka NADH-Q oxidoreductase or NADH dehydrogenase)
Complex II (aka. succinate- Q reductase or succinate dehydrogenase)
Complex III (aka. Q- Cytochrome C oxidoreductase)
Complex IV (aka. cytochrome C oxidase)
What are mobile carriers in the ETC?
Coenzyme Q (ubiquinone) Cytochrome C
Which complexes accept electrons and protons from aqueous solution?
I, II, IV
What happens as electrons pass through each complex?
A proton is passed to the intermembranous space
What is succinate dehydrogenase?
Complex II
An enzyme that enters the TCA cycle and sits in the inner mitochondrial membrane
Uses FAD as a cofactor and can communicate directly with ubiquinone (Coenzyme Q)
As electrons are passed from FADH2 to coenzyme Q, it picks up a pair of protons- this regenerated FAD. and makes QH2
Its a bypass of complex I
How is ATP regenerated?
Protons flowing back into matrix via ATP synthase are used to regenerate ATP
What is a redox reaction?
Electron transfer reaction involving a reduced substrate and an oxidised substrate
What is a redox couple?
A substrate which exists in both oxidised and reduced forms
What is the redox potential?
The ability of a redox couple to accept or donate electrons
How can you measure standard redox potential (E0)?
Use a hydrogen electrode
Positive E0 implies tendency to accept electrons so more oxidant power so more likely to be reduced
Negative E0 implies tendency to donate electrons so more reduction power so more likely to be oxidised
What is ATP synthase?
Makes ATP
Is a multimeric enzyme
Has a membrane bound part (F0) and F1 part which projects into matrix space
What dictates ATP synthesis vs ATP hydrolysis?
direction of H+ flow
What does the oxygen electrode measure?
Measure O2 conc. in a solution housed in a small chamber
What is the base of the sample chamber made of ?
Base of chamber formed by teflon membrane
Underneath membrane is a compartment containing platinum cathode and silver anode
How is oxygen conc. measured?
- Small voltage of 0.6V applies between cathode and anode
- Oxygen diffuses through teflon membrane and is reduced to water at Pt cathode
- Circuit is completed at silver anode which is slowly oxidised to AgCl by KCl electrolyte
- Resulting current is proportionate to O2 conc.
Whats the most common cause of failed oxidative phosphorylation?
Hypoxia and anoxia
What are metabolic poisons?
Molecules that interfere with flow of electrons along ETC or flow of protons through ATP synthase which interrupt ATP synthesis
They’re highly toxic
Name 6 metabolic poisons?
Cyanide + Azide Malonate Rotenone Oligomyocin Dinitrophenol (DNP)
How does cyanide and azide act as a metabolic poison?
Bind with high affinity ferric haem group in cytochrome oxidase (complex IV) blocking final step of ETC
How does malonate act as a metabolic poison?
Closely resembles succinate and acts as a competitive inhibitor of succinate dehydrogenase (Complex II)
Slows down flow of electrons from succinate to ubiquinone
How does rotenone act as a metabolic poison?
An isoflurane found in roots and seeds of some plants. Inhibits transfer of electrons from complex I to ubiquinone
How does oligomycin act as a metabolic poison?
Antibiotic produced by streptomycin
Inhibits OP by binding to stalk of ATP synthase and blocking flow of protons through enzyme
How does DNP act as a metabolic poison?
Proton ionophore which can shuttle protons across inner mitochondrial membranes
How can dinotrophenol induce weight loss?
Uncouples OP from ATP production and increases metabolic rate and body temp.
Used as anti-fat medication but difference between slimming dose and that required for metabolic poisoning is close
Its now used for pesticides and food dye but is illegal to sell for human consumption
