Flashcards in lecture 27 - redox reactions in the mitochondrion Deck (13):
How much NADH is produced in respiration?
For each mol of glucose,
• 2 mol of NADH are produced in glycolysis (cytosolic)
• 2 mol of NADH from oxidation of pyruvate (mitochondrial)
• 6 mol of NADH in the citric acid cycle (mitochondrial).
What is the electron transport chain?
Protein complexes in inner mitochondrial membrane
4 Complexes, of which 3 are on NADH O2
Complex II: Succinate dehydrogenase.
How is NAD+ reduced to NADH?
o = -0.32 V
Remember to look over A level stuff with direction of redox reactions and all that xoxoxo
ok thanks love from future me xoxoxo
WHAT IS THE PATHWAY OF
ELECTRONS FROM NADH ---> O2?
Just like Glycolysis, this is not a single-step reaction:
Multiple steps allow conservation of free energy (as
ATP) at discrete points in pathway.
This reaction sequence is accomplished by the
respiratory chain which is an e-transport pathway.
The enzymes that catalyse the reactions of the
respiratory chain are all membrane-bound: comprises
a large fraction of the proteins of the inner membrane.
What is complex i?
Complex I (NADH – UQ oxidoreductase)
-Catalyses transfer of 2e
from NADH to ubiquinone
NADH oxidized initially by a flavoprotein, containing flavine mono-nucleotide (FMN) as a prosthetic group
-Electrons then passed to Fe/S centres (non-haem iron proteins)
Non-haem iron proteins (FeS):
Each Fe/S centre covalently linked to Cys
residues in protein
-arrangement of FeS clusters forms the ‘electron wire’
inhibited by rotenone/NO
What is complex ii?
Catalyses oxidation of succinate and reduction of UQ
1 flavine adenine dinucleotide (FAD which is reduced to FADH2) covalently bound to protein
-3 Fe/S centres
What is Ubiqinone?
(Coenzyme Q10, CoQ10)
A lipid-soluble component, present in great excess over other constituents of chain, freely diffuses in membrane
oxidised form quinone, reduced form quinol
What is Complex III?
(UQ-Cyt c oxidoreductase)
2 b-type cytochromes (b566 (=bL) and b562 (=bH)
1 Fe/S centre (Rieske protein)
bH inhibited by antimycin
Each cytochrome reduced by 1 e-
Cytochromes:a haem prosthetic group bound to a protein.
The Fe atom coordinated in the porphyrin ring is reduced: Fe3+ --> Fe2+
What is Cytochrome c?
The only component of the respiratory chain which is
not an integral part of the membrane.
Nevertheless, it is bound loosely to the OUTER side
of the inner membrane.
What is complex IV?
(cytochrome c oxidase)
cytochromes a, a3
2 copper atoms (CuA, CuB)
Accepts 4 e- from cyt c (=4 separate turnovers
of cyt c)
When fully reduced, can then reduce O2, together with 4H+ --> 2H2O
Oxygen reduction on matrix side of membrane
Inhibitors: CN, CO, azides (N3)
How can we identify Which Complexes Actually 'Make'
ATP?: Coupling Ratios?
Measure O2 consumption by mitochondria in a closed
chamber with O2 electrode and observe
Mitochondria in Pi buffer
-Background respiration observed with respiratory substrate
-Addition of ADP large increase in respiratory rate. When
ADP is all phosphorylated, rate returns to background rate.
i.e. The e-transport and phosphorylation reactions are
-If a known amount of ADP is added, the amount of O2 used during phosphorylation can be measured to give:
ADP: O2 ratio (P:O ratio)
-P:O ratio is a measure of the number of ATP molecules
synthesized per pair of e- passing down the respiratory chain.