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)
Chlorophylls
Cyanobacteria and
Eukaryotes have
Chlorophyll a
Green and Purple
Bacteria have
Bacteriochlorophylls
The core is a
tetrapyrole ring with a
magnesium molecule.
Accessory Pigments
Prochloron
and
eukaryotes
Eukaryotes
alone
Bind with
proteins;
cyanobacteria
& red algae
• 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 Bacteria
Thermophilic 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
Need a supply of
organics or H2.
Tolerates O2 or S-2.
Some photoautotrophs.
Winogradsky
column
Phototrophy Overview
Purple and Purple Non-Sulfur Bacteria require means of producing
reduced electron carriers; done by reverse electron flow, as with
chemolithoautotrophs.
(or PMF)
Carboxylation
Phase
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.
Ribulose 1,5-bisphosphate
Regeneration
Phase
Reduction
Phase
Anabolism
Nutritional Types Revisited