Chemolithotrophs and Phototrophs

Question 1

Lithotroph

Answer 1

-get their energy from oxidizing inorganic molecules
-prokaryotes only
-many are extremophils
-many use O2 as an external electron acceptor
-mostly autotroph - fix CO2. Need a great deal of reducing power for biosynthetic rxn

Question 2

common electron donors

Answer 2

-H2S, H2, Fe 2+, NH4+

Question 3

ralstonia eutropha

Answer 3

-chemolithotroph
-gram negative
-can grow as a chemolithoautotroph on H2, CO2, and O2 - aerobic conditions
-produces two hydrogenase that split H2 to H+ (oxidize H2) and donate electrons to produce ATP/NADH

Question 4

hydrogenase

Answer 4

-oxidize H2 and donate electrons to produce ATP/NADH
-membrane bound - donates electrons to reduces quinones to ETC - generates proton motive force
-soluble cytoplasmic enzyme that reduces NAD+ to NADH - generates reducing power for biosynthetic reactions

Question 5

Ralstonia eutroph ETC

Answer 5

Question 6

oxidation of sulfure compounds

Answer 6

-chemolithotroph
-common electron donors: hydrogen sulfide, elemental sulfr, thiosulfate, sulfite
-final oxidation product typically sulfate
-elemntal sulfur can be stored in the cell
-high energy electrons funneled inti ETC generates ETC and PMF

Question 7

phototrophs

Answer 7

-use light energy instead of chemical reactions to drive electron flow - generate a PMF to produce ATP
-ATP generated by photophorylation
-some oxygenic others aoxygenic
-most phototrophs are autotrophs, but rare phototrophs that get carbon from organic molecule Z(photoheterotrophs)

Question 8

oxygenic vs aoxygenic

Answer 8

-oxygenic generate O2 as a biproduct of photosynthesis (cyanobacteria, algae)
-anoxygenic do not generate O2. These evolved first (gree sulfure bacters, phototrophic purple bacteria

Question 9

photosynthetic reation centers

Answer 9

-complexes of proteins and pigments where electrons are excited and transferred to ETC
-light sensitive pigments absorb light and transfer energy to ETC: chlorophylls for for oxygenic phototrophs or bacteriochlorophylls for anoxygenix phototrophs

Question 10

antenna pigments

Answer 10

-light harvesting complexes of bacteriochlorphylls that capture light energy and transfer to reaction center
embedded in or associated with the membrane

Question 11

bacteriochlorophyll types

Answer 11

different pigments with different absorbtions ranges allow ifferent phototrophs to coexisst in the same habitat- make use of light others cant use

Question 12

purple bacteria

Answer 12

-anoxygenic
-photosynthetic reaction center contains bacteriochlorophyll (P870) that absorb light energy
-P870 goes from weak electron donor to very strong electron donor
-P870 donates electrons to quinone, enters ETC and generates PMF - ATP synthase makes ATP
-electrons cycle back to P870 to return to its original state - cyclic photophosphylation
-Q type reaction center

Question 13

electron flow

Answer 13

-not all anoxygenic phototrophs have cyclic electron flow - some transfer electrons to external electron acceptor

Question 14

FES type

Answer 14

-electrons transfer to Fe/S cluster carrier - lower E, stronger electron donor therefore higher energy output

Question 15

reducing power

Answer 15

-need to make NADPH for biosynthetic rxns
-electrons for this ultimately come from an external electron donor like H2S-enter quinone pool
-Q-type E not not low enough to reduce NAD+ - use reverse electron flow to do this

Question 16

reverse electron transport

Answer 16

-some autotrophs lack an electron donor with a more negative reduction potenital than NAD+/NADH - how to generate reducing power? Reverse electron transport
-use PMF to drive electrons in opposite direction in ETC to reduce NADP to NADPH

Question 17

oxygenic phototrophs

Answer 17

-two distinct photocenters - Photsystem I (PSI or P700 - FeS type) and photosystem II (PSII, or P680, Q type)
-rxn centers also found in membranes
-chloroplasts contain sacks of thyakoid membranes which contain photosynthetic rxn centers

Question 18

chloroplasts

Answer 18

-phototrophic eukaryotes like algae contain chloroplasts
-chloroplasts evolved from cyanobacteria
-

Question 19

eukaryotes rxn center

Answer 19

-chloroplast thylakoid membranes

Question 20

cyanobacteria rxn center

Answer 20

-specialized lamellar or thylakoid membranes

Question 21

oxygenix phototrophs(PSII)

Answer 21

PSII excited by light and transfers electrons to ETC and becomes highly electropositive
-can accept electrons from water to geenrate hydrogen an d oxygen
-P680 now back to original state and can be excited again
-electrons from PSII passed to quinones, down ETC generating PMF. Ultimately low energy electrons transferred to PSI

Question 22

oxygenic phototroph (PSI)

Answer 22

-PSI (P700), excited by light, transfers electrons recieved from PSII. Ultimately these electrons used to reudce NADP to NADPH
-NADPH subsequently used as electron source for biosynthetic rxn - CO2 fixation
-CO2 ultimate electron acceptor

Question 23

electron flow of oxygenic phototroph

Answer 23