PP as a metabolic process

Question 1

Metabolic diversity

Answer 1

Autotrophs
Photoautotrophs
Chemoautotrophs
Heterotrophs
Mixotrophs

Question 2

Photolithoautotrophs

Answer 2

Energy from sun light (photo)
Electrons from water to generate O (Litho)
Performed by cyanobacteria, algae, plants and prochlorophytes.
Oxygenic reaction

Question 3

Anoxygenic photosynthesis (Photolithoautotrophs)

Answer 3

Performed by purple S, purple non-S, green S bacteria and heliobacteria
Electrons from other reduced substances

Question 4

Chemoautotrophs

Answer 4

Obtain energy from oxidation of reduced substances.
Not as much E as photosynthesis or heterotrophy.
Important roles:
1. N oxidizing bacteria contribute N cycling by oxidizing ammonium to nitrite and nitrate
2. Dissolved minerals and gasses support variety of PPs that support heterotrophs
3. H oxidizing bacteria support hetero bacteria and fungy in pores of rocks as deep as 2800m beneath the surface of the earth.

Question 5

Carbon Fixation

Answer 5

Calvin cycle used by phyotplankton, most significant C fixation path on planet
There are other diverse fixation processes
Incorporation of C into organic molecules
C fixation sources:
Carbon dioxide, methane, methanol or methylamine

Question 6

Ways to fix C into OM

Answer 6

Reductive pentose phosphate or Calvin-Benson-Bassam cycle
Reduced TCA cycle
Reductive acetyl-CoA pathway
3-hydroxypropionate/4-hydroxybutyrate cycle
Dicarboxylate/4hydroxbutyrate cycle
Aerobic autotrophs use CC
Anaerobic chemoautotrophs use E efficient but O sensitive paths

Question 7

PP in the oceans

Answer 7

More than one E source, electron source and way to fix C
Metabolic processes are diverse and widespread, yet poorly understood
Feedbacks have profound impacts on the Earth system

Question 8

Photosynthesis

Answer 8

Light dependent photolysis of water: 2H2O + light –> O2 +4H + 4e-
Light independent: CO2 + 2H + 2e- –> (CH2O) CO2, fixed to form carboxylate

Question 9

Energy and electron carriers

Answer 9

ATP, coenzyme for intracellular E transfer
NADPH, nicotinamide adenine dinucleotide phosphate.
NADPH –> NADP+ + H+ + 2e-
* Light reaction, 2H20 + 2NADP+ + 3ADP + 3Pi → O2 + 2NADPH + 2H+ + 3ATP
* Dark reaction, CO2 + 2NADPH + 2H+ + 3ATP → (CH2O) + H2O + 2NADP+ + 3ADP + 3Pi

Question 10

Photolysis

Answer 10

Donor, water is oxidised
Acceptor, NADPH is reduced
Need +0.82V to split from light
Catalysed by Photosystems
PS2 = P680, highly oxidising
PS1 = P700, highly reducing

Question 11

Light independent reaction

Answer 11

CO2 + 2H2O + 8 photons –> CH2O +H2O + O2
1. Carboxylation phase, enxyme RuBisCo
2. Reduction phase
3. Regeneration phase of RuBP
4. Product synthesis
Sugars and carbs converted to fats, fatty acids, AAs and organic acids.

Question 12

RuBisCo

Answer 12

Catalyses the carboxylation of rubulose-1,5-bisphosphate (RuBP) with carbon dioxide

Question 13

Photorespiration

Answer 13

RuBisCo, RuBP carboxylase-oxygenase
The carboxylation activity can be competitively inhibited by oxygen
RuBisCo is inefficent at current day O concs
Cell requires a high conc of RuBisCo, high carbon dioxide concentrations at active site.

Question 14

Complete equations

Answer 14

Light reaction:
2H2O + 2NADP+ –> O2 + 2NADPH2
Photophosphorylation:
ADP + Pi –> ATP
Dark Reaction:
6CO2 + 12NADPH + 12H+ + 18ATP –>
C6H12O6 + 12NADP+ + 18 ADP + 18Pi + 6H2O

Net Reaction:
6CO2 +12H2O –> 6(CH2O + 6O2 + 6H2O)