Lecture 3B Flashcards
low-potential electron donors (are more _______________)
Electronegative
what happens to low-potential electron donors?
Oxidized
where are the resulting electrons driven through?
Electron transport chain
How is proton motive force (PMF) arise?
Due to movement of electrons
the terminal electron acceptor in Aerobic respirations
Oxygen
How is fermentations different from aerobic respirations
Fermentation: do not require external electron acceptors, generates ATP through subtrate-level phosphorylation
Aerobic respirations: can generate ATP through ETC
mV value of NADH/NAD+
−320 mV
mV value of FADH2/FAD, Em,7
+31 Mv
mV value of
HCO2−/CO2, Em,7 =
−420 mV
mV value of
succinate/fumarate, Em,7 =
+31 mV
mV value of
H2/H+, Em,7 =
−420 mV
mV value of
O2/H2O, Em,7 =
+815 mV
mV value of
NO/N2O, Em,7 =
+1,300 mV
small organic compounds that can donate electrons
Formate and succinate
In Aerobic bac. ETC;
redox spans gives rise to a thermodynamic driving force of more than
1eV
In Aerobic bac. ETC; Each proton transport across the membrane has a thermodynamic cost of around
4.6 Kcal mol^-1
In Aerobic bac. ETC;
with an ~1-V redox span between the initial donor and acceptor, how many protons are pumped for each electron transferred?
Five protons
Why is stepwise drop in potential along the respiratory chain imporant?
It allows for energy conservation rather than dissepated as heat.
also forms an integral part of the proton-motive respiratory machinery
Cell membrane
How does cell membrane forms a important machinery in PMF?
- Provides an isolating layer
- Lipid hydrocarbons establishe proton conduction pathways, and proton uptake
Lipid composition of bacterial cell wall
- zwitterionic
- anionic
- highly glyosylated lipids
a lipid that is 75% in E. coli
Phosphatidylethanolamine
a lipid that is 20% in E. coli
Phosphatidylglycerol
a lipid that is 5% in E. coli
Cardiolipin
lipids that is composed in the Actinobacteria
Phophatidylinositol and phosphatidylinositol mannosides
can switch to alternative electron acceptors
facultative anaerobes
_______ electron acceptors used by facultative organisms include those that are fairly near the O2 /H2O couple, such as many inorganic and organic compounds, and metals such as Fe3+ and Mn4+.
Alternative
These microorganisms use more electronegative electron acceptors often employ enzymes that are inhibited oxygen
Obligated anaerobe
Chemolithotrophs are microbes that conserve energy from the oxidation of inorganic electron donors.
Chemolithotrophy
examples of chemolithotrophy oxidation
- Hydrogen oxidation
- Sulfur oxidation
- iron Oxidation
Simpliest form of chemolithotrophs
Hydrogen bacteria
Final product of classifcal hydrogen bacteria
Water and ATP
the Two Hydrogenase in H2 Oxidation
- membrane-integrated hydrogenase
- cytoplasmic hydrogenase
Why is H2 in oxic environments fleeting?
- Most biological H2 production is the result of fermentation
- H2 is utilized by several anaerobic bacteria and archea
The model for studying H2 Oxidation
gammaproteobacterium Rolstania eutropha
Final oxidation product of H2 Oxidation
Water
Final oxidation product of Sulfur oxidation
Sulfate
Most common sulfur compounds as electron donors
- Elemental sulfur
- Hydrogen Sulfide
- Thiosulfate
- (minor) sulfite
The system that allows sulfur oxidizing bacteria to oxidize sulfur
Sox system
WHich organism is SOX system has been decribe in?
Paracoccus pantotrophus
SOX system contains over ________ encoding various cytochromes and other proteins necessary for the oxidation of reduced sulfur compounds directly to sulfate.
15 genes
Elements of the Sox system are found in diverse ___________
Sulfur chemolithotrops and photrophic sulfur bacteria
organisms that oxidize sulfide to obtain reducing power for CO2 fixation rather than for energy conservation.
Phototrophic sulfur bacteria
Four Keu Proteins in SOX system
SoxXA
SoxYZ
SoxB
SoxCD
The first enzyme in sox system that forms heterosulfide bond between the sulfur compound and SoxYZ
SoxXA
it releases sulfate from oxidatuon of the sulfur compounds
SoxB
sulfur dehydrogenase; a key enzyme that mediates removal of 6e- from sulfur compound bound to SoxYZ
SoxCD
it is used by other organisms in the absence of Sox CD
DSr AB
An enzyme homologous to the enzyme sulfite reductase found in sulfate reducing bacteria
DsrAB
aerobic oxidation of ___ to ___ , supports the growth of chemolithotrophic “iron bacteria”
Ferrous iron (Fe2+) to Ferric ion (Fe3+)
Aerobic respiration of Ferrous to Ferric ion supports what?
Growth of Chemolithotrophic Iron bacteria
pH level of Nitrogen organisms at neutral pH
+0.2
at acidic pH what is the pH of iron organisms?
+0.77V
