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