Cell Integrity Flashcards
Where does oxidative phosphorylation occur?
MItochondria
Where is the bulk of ATP generated within the mitochondria?
Electron transport chain in the inner membrane
What are cristae?
Folds that project inwards
What is the role of cristae?
Increase the surface upon which oxidative phosphorylation can take place
What happens to NADH and FADH2 in the mitochondria?
They are reoxidised by molecular oxygen
What is the equation for the oxidation of NADH?
NADH + H+ + 1/2 O2 —> NAD+ & H2O
What is the equation for the oxidation of FADH2?
FADH2 + H+ + 1/2 O2 —> FAD &H2O
What membrane proteins are present in the ETC?
Complex I (NADH dehydrogenase) Complex II (succinate dehydrogenase) Complex III ( Q- cytochrome C oxioreductose) Complex IV (cytochrome C oxidase)
What are the mobile carriers present in the ETC?
Coenzyme Q (ubiquinone) Cytochrome C
What is the process of the electron transport chain?
Complexes I, II & IV accept e- and a proton (H+) from the aqueous solution.
As the e- pass through each of these complexes, a proton is pumped into the inter membrane space
What is succinate dehydrogenase?
- An enzyme of the TCA cycle
- sits in the inner mitochondrial membrane
- uses FAD as a cofactor
- can communicate directly with coenzyme Q
What happens when complex I is successfully bypassed?
Fewer H+ are pumped to the inter membrane space when FADH2 is reoxidised compared to NADH
FEWER ATP MOLECULES ARE GENERATED FROM THE REOXIDATION OF FADH2
What is the definition of a REDOX reaction?
Electron transfer reactions involving a reduced substrate (which donates e- & is oxidised) and an oxidised substrate (which accepts e- and becomes reduced)
What is the definition of a REDOX couple?
The substrate can exist in both oxidised & reduced forms
NAD+ & NADH
FAD & FADH2
Fe3+ & Fe 2+
1/2 O2 & H2O
What is the definition of a REDOX potential?
The ability of a REDOX couple to accept/donate e-
How can the standard redox potentials (Eo) be measured?
Using a hydrogen electrode as a reference experimentally
(-)ve Eo
The redox couple has a tendency to donate e- and has more reducing power than H
NAD+/ NADH Eo= -0.32V
(+)ve Eo
The redox couple has a tendency to accept e- and therefore has more oxidant power than H
Fe3+/ Fe2+ Eo= + 0.82 V
What happens as the e- progress along the ETC?
They lose energy
The transfer of e- from one complex to another is energetically favourable
What is ATP synthase?
A multi Eric enzyme consisting of a membrane bound part Fo and F1 part which projects into the matrix space
Rotation of the enzyme drives transition states with alternating affinities for ATP & ADP
How does ATP synthase work?
Conformational E flows from the catalytic subunit into the bound ADP and Pi to promote the formation of ATP
CHEMICAL Energy
What the direction of proton flow through ATP synthase determine?
Determines ATP synthesis Vs ATP hydrolysis
ATP synthesis: H+ into the matrix
ATP hydrolysis: H+ out of the matrix into inter membrane space
What is the oxygen electrode?
A device that measures O2 conc in a solution within a small chamber
What are the steps taken for an Oxygen Electrode?
- A small voltage of 0.6V is applied between the anode(+) and the cathode(-)
- O2 diffuses through the Teflon membrane & is reduced to H2O at the Pt cathode
O2 + 4H+ 4e- —> 2H2O - The circuit is completed at the Ag anode which is slowly oxidised to AgCl by the KCl electrolyte
4Ag+ + 4Cl- —> AgCl + 4 e- - Current is proportional to the O2 conc
What are the the steps in the practical to dissect various components of the ETC using an O2 electrode?
- Prepare a suspension of mitochondria and place them in the chamber
- Monitor O2 consumption of the suspension for a set period of time
* can be used to determine the effects of various substrates and inhibitors on the ETC
What is the lifespan of an ATP molecule?
1-5 mins
What is the common cause of a failure of Oxidative phosphorylation?
Lack of O2
HYPOXIA
What is respiratory control?
Uptake of O2 by mitochondria is controlled by the components of ATP production: ATP & Pi
Allows the body to adapt O2 consumption to actual E requirements
What are metabolic poisons?
Molecules that interfere with either the flow of e- along the ETC or the flow of H+ through ATP synthase
What is malonate?
- closely resembles succinate
- acts as a competitive inhibitor of succinate dehydrogenase
How does malonate affect ETC?
It slows down the flow of e- from succinate to ubiquinone by inhibiting the oxidation of succinate to fumarate
How do cyanide (CN-) and azide (N3-) affect the ETC?
Bind with high affinity to the ferric form of the haem group in the cytochrome oxidase complex blocking the final step of ETC
What is rotenone?
-metabolic poison
Isoflavone found in the roots and seeds of some plants
How does rotenone affect the ETC?
It inhibits the transfer of e- from complex I to ubiquinone
What is Dinitrophenol (DTP)?
- metabolic poison
- a proton ionophore
How does Dinitrophenol affect the ETC?
Shuttles protons across the inner mitochondrial membrane
What is oligomycin?
- metabolic poison
- antibiotic produced by streptomyces
How does oligomycin affect the ETC?
It inhibits oxidative phosphorylation by binding to the ‘stalk’ of ATP synthase & blocking the flow of protons through the enzyme
