Chapter 14 Flashcards
reduction potential
accept electrons (mV) • Positive value of E has -DG
more positive values
represent stronger electron acceptors
ETS is embedded in a membrane that
separates two aqueous compartments. transfers e-
where is ets in gram neg?
inner (cytoplasmic) membrane
Oxidoreductases
oxidize one substrate and reduce another
Cytochromes
colored proteins that absorb visible light
when there is change in redox state
absorbance spectrum shifts
ets transfer electrons
with small reversible energy transitions (iron, copper, double bonds). need cofactors: small molecules that associate w/ protein
ets requires 3 components
- Initial substrate oxidoreductase (or dehydrogenase)
- Mobile electron carrier
- Terminal oxidase
Initial substrate oxidoreductase
• 2e- from NADH enter and passed onto NADH dehydrogenase
• Cofactors ”hand-off” e- to each other (connections)
• Electrons are transferred to a quinone (Q)
pumps 4 H+ across membrane
mobile electron carrier
- Quinone gets 2e- from substrate oxidoreductase w/ 2H+ to balance neg charges
- Q reduced to QH2
- Quinols carry reduction energy to other ETS
- After transferring 2e-, 2H+ are released
terminal oxidase
receives electrons from (QH2) and transfers them to TEA
Bacteria produce several alternate ETS protein complexes
• Initial substrate oxidoreductase (or dehydrogenase)
• Mobile electron carrier
• Terminal oxidase
- doesnt require H+
- Different oxidoreductase complexes interact with different quniones
- Vary in number of cytoplasmic protons pumped
Chemiosmotic theory
energy from e- transfer bw membrane proteins is used to pump protons across membrane, accumulating higher H+ concentration outside membrane
proton motive force Dp
stores energy used to make atp.
pH difference
[pH(in) – pH(out)]
electrical potential
separation of charge bw cytoplasm (more negative) and the solution outside membrane (more positive)
Oxidative phosphorylation
H+ pumped by ETS drive phosphorylation of ADP to ATP by ATP synthase
in a given environment
bacteria use the strongest electron donor and strongest electron acceptor available
Dissimilatory denitrification
reduction of oxidized states of nitrogen
NO3->NO2- >NO–>1⁄2 N2O–>1⁄2 N2
Assimilatory reduction
generates ammonium ion for fixation
Redox potentials for
oxygen forms of sulfur:
Sulfur lower than oxidized N
SO42- –>SO32- –> 1⁄2 S2O32- –>S0–>H2S
The metal reduced as a TEA is excluded from the cell
- Iron (Fe3+àFe2+)
- Manganese (Mn4+àMn2+)
- Uranium (U6+àU4+)
- Gold (Au3+àAu)
- Arsenic (As5+àAs3+)
Lithotrophy
electron donor for ets
Methanogenesis
reducing co2 and other single-carbo compounds to form methane
allolactose acts as
inducer
