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Phototrophs• Photophosphorylation for ATP generation:
– still requires a PMF and ATP synthase, – light as an energy input instead of NADH (or reduced
inorganic compound) oxidation.• Photosynthesis (photoautotrophs):
– Light Reactions• Cyclic Photophosphorylation (Photosystem I = PSI)• Non-Cyclic Photophosphorylation (Photosystem II = PSII)
– Dark Reactions (Calvin Cycle)• Photopigments:
– Chlorophylls; carotenoids; phycobiliproteins– Antenna (hundreds of pigment molecules to capture light)– Reaction-center chlorophyll (the link to electron transport)
ChlorophyllsCyanobacteria and Eukaryotes have Chlorophyll a
Green and Purple Bacteria have Bacteriochlorophylls
The core is a tetrapyrole ring with a magnesium molecule.
Accessory Pigments
Bind with proteins; cyanobacteria & red algae
Prochloron and
eukaryotes
Eukaryotes alone
• Different phototrophs have different pigments.
• Pigments absorb light at unique wavelengths.
• Wavelengths of light reaching an environment can be different.
• Phototrophs best equipped to absorb available wavelengths in a given environment yield more energy.
Cyclic Photophosphorylation(PS I)
Absorbs wavelengths ≥680 nm (P700)
Non-Cyclic Phosphorylation(PSII)
Absorbs wavelengths ≤680 nm (P680)
Z-scheme
NADP+
Green Sulfur Bacteria, Chlorobium
Live in anoxic sulfide rich habitats.
Sº accumulates outside the cell.
Cyclic for ATP or non-cyclic to reduce NAD+.
Green Non-Sulfur BacteriaThermophilic using organic matter for electron donor in
photoheterotrphy; H2 for photoautotrophy (e.g. Chloroflexus).
Purple Sulfur Bacteria
• Live in sulfide rich and anoxic habitats.
• Anoxygenic photoautotroph.
• So accumulates intracellularly as inclusion bodies.
Purple Non-Sulfur, Rhodobacter
Winogradskycolumn
Need a supply of organics or H2.
Tolerates O2 or S-2.
Some photoautotrophs.
Phototrophy Overview
(or PMF)
Purple and Purple Non-Sulfur Bacteria require means of producing reduced electron carriers; done by reverse electron flow, as with chemolithoautotrophs.
Calvin Cycle
Fixation of 3 Carbon Dioxide molecules to one molecule of Glyceraldehyde 3-Phosphate (G3P) via carboxylation & reduction requires 3 cycles.
Each cycle requires regeneration of Ribulose 1,5-bisphosphate (RuBP) to fix the next CO2 via the enzyme RuBP Carboxylase.
Regeneration of RuBP from 5 G3Ps follows a reversal of the PPP.
6 cycles will yield 2 G3Ps, which can form a hexose via Gluconeogenesis.
Carboxylation Phase
Reduction Phase
Ribulose 1,5-bisphosphate
Regeneration Phase
Anabolism
Nutritional Types Revisited