5-4: Chemolithotrophs & Phototrophs

Question 1

What is a chemolithotroph

Answer 1

Get energy from oxidizing inorganic molecule (minerals)

Question 2

What types of organisms are chemolithotrophs?

Answer 2

Prokaryotes only

Question 3

Where are chemolithotrophs found

Answer 3

Anywhere with a source of reduced inorganic compounds, but most are extremophiles

Question 4

What are some common electron donors (energy sources) of chemolithotrophs

Answer 4

H2S, H2, Fe2+, NH4

Question 5

Can chemolithotrophs be aerobic?

Answer 5

Yes! Many still use O2 external electron acceptor for respiration

Question 6

Are chemolithotrophs usually autotrophs or heterotrophs?

Answer 6

Autotrophs - fix inorganic CO2

Question 7

Give an example of a chemolithotrophic microbe

Answer 7

Ralstonia eutropha

Question 8

Describe Ralstonia eutropha

Answer 8

G (-) in soil, freshwater
Chemolithotroph using H2, CO2, O2
Has two hydrogenase enzymes that convert H2 to H+ (electron donor to NADH)

Question 9

What are the two types of hydrogenase enzymes in Ralstonia eutropha?

Answer 9

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

Question 10

What are some common sulfur based electron donors?

Answer 10

Hydrogen sulfide (H2S)
Sulfur
Thiosulfate (S2O3 2-)
Sulfite (SO3 2-)

Question 11

What is the typical final oxidation product produced by organisms that oxidize sulfur?

Answer 11

Sulfate SO4 2-

Question 12

How is ATP generated in phototrophs?

Answer 12

Photophosphorylation

Question 13

What are oxygenic phototrophs? E.g.?

Answer 13

Generate O2 as a biproduct of photosynthesis
e.g. cyanobacteria

Question 14

What is a phototroph that does not generate O2? Eg?

Answer 14

Anoxygenic phototroph
e.g. green sulfur bacteria, phototrophic purple bacteria

Question 15

What are photoheterotrophs?

Answer 15

Phototrophs that use carbon from organic compounds

Question 16

What are photosynthetic reaction centers?

Answer 16

Complexes of proteins/pigments where electrons are excited and transferred to ETC

Question 17

What are antenna pigments? What pigment is used on oxygenic organisms? What about anoxygenic?

Answer 17

Light-harvesting complexes that capture light energy and transfer to a reaction center
Oxygenic = chlorophylls
Anoxygenic = bacteriochlorophylls

Question 18

How many bacteriochlorophylls are there? Why are there different ones?

Answer 18

Many, each with different pigmentations/absorption ranges allowing different phototrophs to coexist in same habitat (use different light)

Question 19

Purple bacteria are what kind of phototroph?

Answer 19

Anoxygenic

Question 20

What is the photosynthetic reaction center in purple bacteria?

Answer 20

Bacteriochlorphyll (P870)

Question 21

Describe the ETC of purple bacteria

Answer 21

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

Question 22

What is cyclic phosphorylation?

Answer 22

Electrons from purple bacteria cycle back to P870 and return it to its original state

Question 23

What is a Q-type reaction center? eg?

Answer 23

Electrons transferred to a quinone
e.g. purple bacteria

Question 24

What are FeS type reaction center?

Answer 24

Used by some anoxygenic phototrophs. Transfers electron to Fe/S cluster, which has lower reduction potential (strong electron donor)

Question 25

Do all anoxygenic phototrophs use cyclic electron flow?

Answer 25

No. Some transfer electron to an external electron acceptor

Question 26

If an autotroph lacks an electron donor with a more negative reduction potential than NAD+/NADH how do they generate reducing power?

Answer 26

Reverse electron transport - proton motive force used to drive e in opposite direction of ETC = reduce NAD to NADH (takes a lot of E)

Question 27

What molecules are essential for biosynthetic reactions?

Answer 27

NADH/NADPH

Question 28

What problem do some organisms have when generating NAD(P)H?

Answer 28

Q type reduction potential is not low enough to reduce NAD+

Question 29

What are the two photocenters found in oxygenic phototrophs?

Answer 29

Photosystem 1 (PSI, P700, FeS-type)
Photosystem 2 (PSII, P680, Q-type)

Question 30

Where are the photocentres of oxygenic phototrophs found?

Answer 30

Lamellar or thylakoid membranes

Question 31

How are photocenters organized in chloroplasts?

Answer 31

Chloroplasts contain stacks of thylakoid membranes which contain the photosynthetic reaction centers