5-4: Chemolithotrophs & Phototrophs Flashcards
What is a chemolithotroph
Get energy from oxidizing inorganic molecule (minerals)
What types of organisms are chemolithotrophs?
Prokaryotes only
Where are chemolithotrophs found
Anywhere with a source of reduced inorganic compounds, but most are extremophiles
What are some common electron donors (energy sources) of chemolithotrophs
H2S, H2, Fe2+, NH4
Can chemolithotrophs be aerobic?
Yes! Many still use O2 external electron acceptor for respiration
Are chemolithotrophs usually autotrophs or heterotrophs?
Autotrophs - fix inorganic CO2
Give an example of a chemolithotrophic microbe
Ralstonia eutropha
Describe Ralstonia eutropha
G (-) in soil, freshwater
Chemolithotroph using H2, CO2, O2
Has two hydrogenase enzymes that convert H2 to H+ (electron donor to NADH)
What are the two types of hydrogenase enzymes in Ralstonia eutropha?
Membrane bound enzyme: donates e- to quinones in ETC to generate a proton motive force/ATP
Soluble cytoplasmic enzyme: reduces NAD+ to NADH to make reducing power for biosynthetic reactions
What are some common sulfur based electron donors?
Hydrogen sulfide (H2S)
Sulfur
Thiosulfate (S2O3 2-)
Sulfite (SO3 2-)
What is the typical final oxidation product produced by organisms that oxidize sulfur?
Sulfate SO4 2-
How is ATP generated in phototrophs?
Photophosphorylation
What are oxygenic phototrophs? E.g.?
Generate O2 as a biproduct of photosynthesis
e.g. cyanobacteria
What is a phototroph that does not generate O2? Eg?
Anoxygenic phototroph
e.g. green sulfur bacteria, phototrophic purple bacteria
What are photoheterotrophs?
Phototrophs that use carbon from organic compounds
What are photosynthetic reaction centers?
Complexes of proteins/pigments where electrons are excited and transferred to ETC
What are antenna pigments? What pigment is used on oxygenic organisms? What about anoxygenic?
Light-harvesting complexes that capture light energy and transfer to a reaction center
Oxygenic = chlorophylls
Anoxygenic = bacteriochlorophylls
How many bacteriochlorophylls are there? Why are there different ones?
Many, each with different pigmentations/absorption ranges allowing different phototrophs to coexist in same habitat (use different light)
Purple bacteria are what kind of phototroph?
Anoxygenic
What is the photosynthetic reaction center in purple bacteria?
Bacteriochlorphyll (P870)
Describe the ETC of purple bacteria
P870 absorbs light E, which goes from weak e donor to strong e donor P870*, which donates e- to quinone, enters ETC and generates a PMF. ATP synthase makes ATP
What is cyclic phosphorylation?
Electrons from purple bacteria cycle back to P870 and return it to its original state
What is a Q-type reaction center? eg?
Electrons transferred to a quinone
e.g. purple bacteria
What are FeS type reaction center?
Used by some anoxygenic phototrophs. Transfers electron to Fe/S cluster, which has lower reduction potential (strong electron donor)
Do all anoxygenic phototrophs use cyclic electron flow?
No. Some transfer electron to an external electron acceptor
If an autotroph lacks an electron donor with a more negative reduction potential than NAD+/NADH how do they generate reducing power?
Reverse electron transport - proton motive force used to drive e in opposite direction of ETC = reduce NAD to NADH (takes a lot of E)
What molecules are essential for biosynthetic reactions?
NADH/NADPH
What problem do some organisms have when generating NAD(P)H?
Q type reduction potential is not low enough to reduce NAD+
What are the two photocenters found in oxygenic phototrophs?
Photosystem 1 (PSI, P700, FeS-type)
Photosystem 2 (PSII, P680, Q-type)
Where are the photocentres of oxygenic phototrophs found?
Lamellar or thylakoid membranes
How are photocenters organized in chloroplasts?
Chloroplasts contain stacks of thylakoid membranes which contain the photosynthetic reaction centers
