Flashcards
Lectures 29+30 (Oxidative phosphorylation)
Cards in this deck (36)
- 1Where does oxidative phosphorylation occur?Across the mitochondrial inner membrane
- 2What is oxidised and reduced during oxidative phosphorylation?NADH and FADH2 oxidised, electrons produced pass along a chain of acceptors to O2 which gets reduced to water
- 3How does the respiratory electron transport chain work?NADH and succinate are oxidised at complex I and II respectively. The electrons are transferred to oxygen via complexes III and IV, reducing it to water. The electron transfer is coupled to proton transfer across the membrane into the intermembrane space. The electron transport chain is a ‘downhill’ (energetically favourable) flow of electrons from a negative (-320 mV NADH/NAD+ couple) to a positive redox potential (+820 mV for the O2/H2O redox couple) via a series of sequential redox reactions, in each reaction the donor is oxidised and the acceptor is reduced.
- 4How is oxidative phosphorylation carried out?The proton transfer reactions lead to formation of a proton gradient
(Δp or pmf ) across the MIM which is harnessed by ATP synthase to
make ATP (oxidative phosphorylation). - 5How many protons are transferred across the MIM for each NADH oxidised and how much ATP is produced?10 protons
takes 4 protons to form one ATP, so 2.5 ATP - 6How many protons are transferred across the MIM for every succinate oxidised and how much ATP is produced?6 protons and 1.5 ATP
- 7Describe how redox potentials work- The redox potential is a measure of the affinity of a redox couple for electrons.
- The more negative the redox potential the more likely the redox couple is to donate electrons (thus acting as a reductant)
- The more positive the redox potential the more likely the redox couple is to accept electrons (thus acting as an oxidant). - 8What is chemiosmotic coupling?Using the free energy produced by electrons travelling from a negative to positive redox potential to do work ( pumping protons across the membrane)
- 9How are redox potentials measured?The redox potential (E) of a
molecule is measured using two
half cells linked together, one
containing equimolar amounts of
the substance ‘A’ to be measured
in its oxidised and reduced states
the other containing a 1M solution
of H+ (ox) and 1 atmosphere
pressure of H2 gas (red). If electrons flow from the hydrogen half cell to substance ‘A’ half cell
its redox potential is more positive than hydrogen’s, if electrons flow
to the hydrogen half cell its redox potential is more negative.
- 10What is the redox potential for the oxidation of NADH?-320mV
- 11How is standard free energy change calculated?Change in redox potential = E0’ (acceptor) - E0’ (donor)
ΔG˚= -nFΔE0’ , where F is the Faraday constant and n is the number of
electrons transferred. - 12How is the redox potential of a couple in biological conditions calculated?E’ = E0’ + (RT/nF) ln [Ox]/[Red]
311 K is body temp, n is number of
electrons transferred, F is Faraday constant,
R is the gas constant. - 13What happens to redox potential if the concentration of electrons increases?Becomes more negative
- 14How many ATPs are made in oxidative phosphorylation per glucose molecule assuming a H+/ATP ratio of 4?28
- 15How many ATPs are produced overall per molecule of glucose metabolised?32
2 in glycolysis, 2 in krebs cycle and the rest in ox phosphorylation - 16How many ATPs are produced overall per 18 carbon fatty acid (stearic acid)125
9 in krebs, 117 in ox phosporylation and 1 is used in beta oxidation - 17What does complex I do?Aka NADH dehydrogenase - oxidises NADH to NAD+ and uses the two electrons to reduce a lipid soluble electron carrier, ubiquinone (UQ). Upon reduction with 2 electrons the
ubiquinone binds 2 protons from
the matrix forming UQH2. The free
energy released is used by the
complex to directly pump 4
protons across the inner
mitochondrial membrane. - 18What's the overall reaction carried out by complex I?NADH + 5H+matrix + UQ ----> UQH2 + NAD+ + 4H+intermembrane space
- 19Describe the structure of complex IThe matrix arm of the complex
contains the electron transfer cofactors
which include an FMN
(Flavin mononucleotide) and 9
iron-sulphur clusters, these link
the NADH and ubiquinone
reaction sites, the 2 electrons are
passed between the co-factors. The membrane domain of the complex pumps protons across it.
- 20What does the flavin mononucleotide(FMN) co factor do?Oxidises NADH
- 21What do iron sulphur clusters do?Electrons pass through them to get delivered to ubiquinone. The clusters undergo redox reactions without binding and releasing protons cycling between Fe2+ and Fe3+ oxidation states.
- 22Draw the structures of oxidised and reduced FMN
- 23How does complex I pump protons?It changes its conformation induced by the free energy released during the transfer of electrons from NADH to ubiquinone
- 24What does complex II do?The succinate dehydrogenase
complex oxidises succinate to
fumarate as part of the Krebs cycle
and uses the two electrons to reduce
a lipid soluble electron carrier,
ubiquinone (UQ). Upon reduction
with 2 electrons the ubiquinone
binds 2 protons from the matrix
forming UQH2. No protons are
directly pumped by this complex. - 25Give the overall equation carried out by complex IIsuccinate + UQ + 2H+ matrix ----> fumarate + UQH2
- 26Describe how electron are transferred through complex IIThe electrons from the succinate
reaction site in the matrix arm of the
complex are passed first to a bound
FAD, then via 3 iron-sulphur clusters
and finally via a bound haem
molecule to the ubiquinone reaction
site.
- 27What is ubiquinone?A lipid soluble electron carrier that takes electrons from Complex I
and II to Complex III. It takes up protons from the matrix when
reduced and releases them to the intermembrane space when
oxidised (proton translocation).
- 28What does complex III do?Complex III (cytochrome bc1) oxidises UQH2 to UQ
and transfers the electrons to the
small soluble electron transfer
protein, cytochrome c, the
protons from UQH2 are released
into the intermembrane space
(proton translocation). 2 additional
protons are translocated from the
matrix to the intermembrane
space for every UQH2 oxidised
(Q-cycle). - 29Give the overall equation carried out by complex IIIUQH2 + 2Cytc ox + 2H+matrix ----> 2Cyt c red + 4H+intermembrane space
- 30Describe the Q cycle2 electrons from oxidation of
Ubiquinol (1) are passed along
two separate co-factor chains.
The first goes via an Fe-S cluster
and a haem to reduce Cyt c, the
second goes via two haems to
reduce another ubiquinone (2).
Once a second ubiquinol is
oxidised at site (1), a ubiquinol
can be generated at site (2). This doubles the number of protons translocated per UQH2 oxidised.
- 31What is cytochrome c?A small (~10kD) soluble protein electron carrier. Each cyt c molecule
binds 1 electron, reducing the Fe3+ to Fe2+ in the bound haem cofactor.
Cyt c resides in the inter membrane space.
- 32What does complex IV do?Complex IV (Cytochrome c oxidase) transfers e- from cyt c to
O2, 2 e- from 2 molecules of cyt c
and 2 protons from the matrix are
needed to reduce ½O2 to a
molecule of H2O, using the free
energy released in the reaction 2
protons are directly pumped from
the matrix to the intermembrane
space. - 33What is the overall equation carried out by complex IV?2Cyt cred + 4H+matrix + ½O2 ----> 2Cyt cox + H2O + 2H+intermembrane space
- 34How are electrons transferred across complex IV?2 electrons from 2 cyt c molecule
are passed via a pair of bound
copper ion co-factors to a haem
and finally to a haem/copper pair.
The copper ions cycle between the
Cu+ and Cu2+ oxidation states. The
electrons are used to reduce oxygen
to water.
- 35How many protons are pumped across the membrane for every NADH?10
- 36How many protons are pumped across the membrane for every succinate?6
Information
- Description
- BSci Biochemistry Flashcards on Lectures 29+30 (Oxidative phosphorylation), created by Kayla Price on 28/04/2018.
- Created by
- Kayla Price
- Views
- 1
- Rating
More on Electron Transport and Oxidative Phosphorylation