Exam 2: Flashcards
Redox reaction
Reaction in which electrons move from a donor (reductant/reducing agent) to an acceptor (oxidant/oxidizing agent)
Reducing agent
Electron donor in a redox reaction
Oxidizing agent
Electron acceptor in a redox reaction
E’
Standard reduction (electrode) potential The equilibrium constant for a redox reaction Measure of the tendency of the reductant to lose electrons More negative reduction potential = more likely to donate (electrons flow towards final acceptor which has the highest potential)
deltaG naught’
Free energy released when electrons move from a reductant to an oxidant with a more positive potential
= -nFdeltaE’ where n = # electrons transferred, F = Faraday constant, and delta E’ = (E’acceptor - E’donor)
Faraday constant
96.5kJ/mole/volt
Types of electron carriers
Flavoproteins
Quinones
Iron-sulfur proteins
Cytochromes
Flavoproteins
Protein-composed hydrogen and electron carrier molecules containing Flavin prosthetic group which bonds the H+ and e-
e.g. FAD, FMN
Quinones
Lipid-composed hydrogen and electron carrier molecules, contain benzyl ring which confers electron carrying ability
e.g. coenzyme Q, ubiquinone
Iron-sulfur proteins
Protein-composed electron carriers containing FeS clusters that act as prosthetic groups to bond the e-
e.g. Ferridoxin
Cytochromes
Protein-composed electron carriers with heme prosthetic group that binds the e-
e.g. cytochrome c
Complex I
NADH-ubiquinone oxioreductase
First complex in ETC
Coupled to proton extrusion
Complex II
FADH2-succinate dehydrogenase
Second complex in ETC
Not coupled to proton extrusion
Complex III
Ubiquinone-cytochrome c oxidoreductase, AKA bc1 complex
Third complex in ETC
Coupled to proton extrusion
Complex IV
Cytochrome c oxidase, AKA cytochrome aa3
Fourth complex in ETC
Coupled to proton extrusion
Coupling sites
Complexes in the ETC that couple electron transfer with extrusion of protons, generating a proton gradient across the membrane that contributes to the proton motive force
protons extruded by ETC after electron donation by NADH
6 (donates to complex I, therefore three coupling sites are involved which each extrude 2 protons)
protons extruded by ETC after electron donation by FADH2
4 (donates to complex II, therefore two coupling sites are involved which each extrude 2 protons)
Differences in bacterial ETC compared to mitochondrial
- Different pathways to oxygen
- e.g. may send electrons to cyt 0 either after CII or CIII, bypassing CIV or CIII and CIV - Different final acceptor than oxygen
- e.g. nitrate (inorganic), fumarate (organic)
Photobacterium electron transport chain
ETC generates light
NADH donates electrons to flavoprotein, which shunts them to FMN (instead of the cytochrome complexes)
Electrons are then transferred to O2 in a process that uses an enzyme called luciferase and a long chain hydrocarbon to generate light
Both FMN and the hydrocarbon are oxidized as oxygen is reduced
Usually only use this pathway when colonizing tissues of marine animals (symbiotic, help fish to attract mates and deter predators)
Oxidative phosphorylation
Process by which energy (proton gradient) from ETC is used to make ATP
ATP synthesis driven by influx of protons and catalyzed by F1F0ATPase
1 ATP generated for every 2 protons extruded by ETC that pass through ATPase on the way back in
Chemiosmotic Theory
Membranes pump protons out, generating gradient that can then be used to do useful work (e.g. generation of ATP, flagella rotation, solute transport)
deltaP
Proton motive force (mV)
Sum of all charges (proton concentration gradient and other) between cytoplasm and outside of cell
deltaP = deltaPsi - 60 delta(pH)
Most bacteria maintain deltaP between -60mV (minimum needed to do work) and -200mV (max membrane can withstand)
delta Psi
All charges of the membrane potential except the proton gradient, contributes to the deltaP of a membrane
delta pH
The proton gradient accross membrane, contributes to the deltaP
Relative contribution of delta Psi and delta pH to delta P in neutrophiles
both delta psi and delta pH contribute to delta P
Relative contribution of delta Psi and delta pH to delta P in acidophiles
delta P almost entirely contributed by delta pH
Relative contribution of delta Psi and delta pH to delta P in alkaliphiles
delta P almost entirely contributed by delta Psi
Measurement of delta Psi
Measured indirectly using a cation combined with an ionophore or a lipophilic cation
Measurement of delta pH
Add radioactively labelled weak acid or base, uncharged molecule freely diffuses, becomes protonated (weak acid) or deprotonated (weak base) - measure radioactivity taken up by cells
for a weak acid:
