OXPHOS Flashcards
what is the primary function of the mitochondria?
to convert organic materials into energy in the form of ATP via the process of oxidative phosphorylation
what are the major products of glycolysis and where are they oxidised?
pyruvate and NADH, in the mitochondria
what is the outer mitochondrial membrane permeable to?
small molecules and ions
what is the inner mitochondrial membrane permeable to?
most small molecules and ions
what is the function of the outer mitochondrial membrane?
separate mitochondria from the cytosol
what is contained in the inner mitochondrial membrane?
- respiratory chain supercomplexes
- ADP-ATP translocase
- ATP synthase
what is contained within the mitochondrial matrix?
-pyruvate dehydrogenase
-citric acid cycle enzymes
-fatty acid B-oxidation enzymes
-amino acid oxidation enzymes
-DNA
-ribosomes
ATP, Pi
ions
what is the chemiosmotic mechanism for ATP synthesis?
1) reduced substrate donates e-
2) electron carriers pump H+ out as electrons flow to O2
3) energy of e- flow is stored as electrochemical potential
4) ATP synthase uses electrochemical potential to generate ATP
apart from ATP synthesis, what are the other roles of the mitochondria?
- biosynthesis of porphyrins
- fatty acid oxidation
- apoptosis
- regulation of cellular redox state
what is the primary function of chloroplasts?
capture and convert light energy into chemical energy, and store this in molecules of carbohydrates
what are three similarities between oxidative phosphorylation and photophosphorylation?
1) both processes involve electron flow through a series of membrane bound carriers
2) energy made available from downhill electron flow can be used to transport protons across proton-impermeable membrane
3) free energy for ATP synthesis via ATP synthase is generated by the flow of protons back up their carrier proteins
how is the mitochondrial genome structured?
circular molecule with no histones; encodes 2 rRNAs and 22 tRNAs. produces 13 polypeptides plus some subunits of other proteins
what is the endosymbiotic theory?
mitochondria and chloroplasts evolved from separate prokaryotes which were taken inside the cell as endosymbionts
what evidence is there for the endosymbiotic theory?
- mitochondria and chloroplasts have their own DNA, which is circular
- mitochondrial ribosomes resemble 70S ribosomes in bacteria
- phylogenetic analysis: mitochondrially encoded proteins cluster as a subgroup of a-proteobacteria
in the equilibrium between ATP ADP + Pi, when is ATP synthesised and hydrolysed?
synthesised: if delta G is less than 0
hydrolysed: if delta G is greater than 0
what is the purpose of cristae?
large surface area, allows for generation of membrane potential
what is the deltapH for the mitochondria?
intermembrane space - pH 7
matrix - pH 8
deltapH - 1
what is the deltapH for chloroplasts?
intermembrane space - pH 7
thylakoid - pH 5
stroma - pH 7/8
delta pH 3
what does delta pH refer to?
the difference in pH between compartments, a larger deltapH indicates a larger driving force for reaction
what constitutes an electrochemical potential?
chemical and electrical potential of protons across the mitochondrial membrane
what gives rise to chemical potential?
delta pH
what gives rise to electrical potential?
difference in proton concentrations - cause a charge difference across the membrane
what is the role of NADH and FADH2 in the metabolism of glucose?
transient energy storage, eventually oxidation in the electron transport chain to provide energy for ATP synthesis
how does electron transfer occur in the ETC?
NADH _> ubiquitone -> cytochrome c -> oxygen
when does ubiquinone act as an electron carrier?
when bound to a protein where the semiquinone radical can be stabilised by the protein environment
how is ubiquinone anchored to the membrane?
through hydrophobic isoprene tail
when is a redox reaction energetically favourable?
when deltaE is positive, overall deltaG is negative. the reaction is exergonic and thermodynamically favourable
what is the role of complex II?
directly links the ETC to TCA cycle. electrons from fumerate are transferred to FADH2, and accepted by ubiquinone
how do we know the reactions which occur in complex II are not coupled to proton transport?
the gain in free energy from oxidising FADH2 and reducing ubiquinone is virtually zero, there is insufficient energy to couple the redox reaction to proton transport
which processes take place in the mitochondrial matrix?
oxidation of pyruvate and the citric acid cycle
what is the advantage of having downhill electron flow coupled to uphill transport of proteins across a proton impermeable membrane?
conserves free energy of fuel oxidation as a transmembrane electrochemical potential
why does the inner mitochondrial membrane have no porins?
makes it highly impermeable, and therefore able to generate a membrane potential
what is indicated by a larger delta pH?
larger driving force for a reaction
what is complex I called?
NADH: ubiquinone oxidoreductase or NADH dehydrogenase
how are electron carriers in the ETC organised?
the four complexes of the ETC are connected by mobile electron carriers, they also have bound electron carriers to separate reduction and oxidation in space
what are the mobile electron sources in the respiratory chain?
- Nicotinamide adenine dinucleotide (NAD+/NADH)
- Flavin adenine dinucleotide (FAD/FADH2)
how many electrons can cytochromes carry?
one at a time
name 2 cytochromes
- heme
- iron-sulfur centres
what does the difference in standard reduction potential measure?
standard free energy change for the transfer of an electron from one molecule to another
what was found from structure experiments into complex I of T. thermophilus?
- there are three subunits in eukaryotes that are structurally similar to sodium/proton antiporters
- there was an unexpected long a-helix perpendicular to the membrane
what is the proposed model for proton translocation by complex I?
pairs of electrons from NADH are passed along a chain of iron-sulfur clusters, eventually reaching ubiquinone
what prosthetic groups are found in complex I?
non-covalently bound FMN and iron-sulfur clusters
what type of diseases are mutations to complex I associated with?
neurodegenerative diseases
what is complex I?
a proton pump driven by energy of electron transfer. this is vectorial
what is the structure of complex I?
L shaped, with one arm in the membrane and the other extending into the matrix
what two coupled reactions are catalysed by complexI?
1- exergonic transfer of a hydride ion from NADH and a proton from the matrix to ubiquinone
2- endergonic transfer of 4H+ from the matrix to inter membrane space
what is the role of complex II?
provides ubiquinol to be utilised in complex III
what is the structure of complex II?
contains four subunits: a, b, c and d
A - FADH2 and succinate binding site
B - 3 iron sulphur clusters
C + D - heme group and quinone binding site
what happens in complex II?
succinate comes in and is reduced to fumerate, electrons are transferred to FADH2 and electron transfer occurs, ubiquinone is reduced
what is complex III?
cytochrome c reductase
which three subunits are present in all species in complex III?
cytochrome b, cytochrome c1 and rieske protein
why are 2 cytochrome cs required in complex III?
2 electrons are needed for the fully reduced ubiquinol, each cytochrome can only carry one
what is the structure of complex III?
cytochrome c is located close to c1, to allow electron hopping. cytochrome b carries 2 heme groups and Rieske protein contains an iron-sulfur cluster
what is the role of complex III?
couples transfer of electrons from ubiquinol to cytochrome c with the vectorial transfer of protons from the matrix to inter membrane space
what is the purpose of the Q cycle?
to accommodate the switch between the 2e- electron carrier ubiquinol and one e electron carriers heme bL and bH
what is the net effect of the Q cycle?
QH2 is oxidised to Q, 2 cytochrome Cs are reduced and protons are moved from P space to N space
what is complex IV?
cytochrome oxidase
what is the role of complex IV?
accepts electrons from reduced cytochrome c and transports them to molecular oxygen for reduction to water
what structures are important in complex IV?
cytochromes and copper centres
one cytochrome and one copper centre form a binuclear centre, the site of oxygen reduction
why does the reduction of O2 in complex IV need to be tightly controlled?
to avoid the escape of intermediates and generation of ROS
