Anoxygenic photosynthesis

Instead of a chlorophyll-type receptor and electron transport chain, proteins such as halorhodopsin capture light energy with the aid of diterpenes to move ions against a gradient and produce ATP via chemiosmosis in the manner of mitochondria.

The photopigments used to carry out anaerobic photosynthesis are similar to chlorophyll but differ in molecular detail and peak wavelength of light absorbed.

This differs from chlorophyll a, the predominant plant and cyanobacteria pigment, which has peak absorption wavelength approximately 100 nanometers shorter (in the red portion of the visible spectrum).

[3][5] The electron transport chain of green sulfur bacteria—such as is present in the model organism Chlorobaculum tepidum—uses the reaction center bacteriochlorophyll pair, P840.

The electron transport chain of purple non-sulfur bacteria begins when the reaction center bacteriochlorophyll pair, P870, becomes excited from the absorption of light.

Sulfide is used as a reducing agent during photosynthesis in green and sulfur bacteria.
  1. Energy in the form of sunlight
  2. The light dependent reactions take place when the light excites a reaction center, which donates an electron to another molecule and starts the electron transport chain to produce ATP and NADPH.
  3. Once NADPH has been produced, the Calvin cycle [ 1 ] proceeds as in oxygenic photosynthesis, turning CO 2 into glucose.
Different Reaction Centers (RC) for photosynthetic organisms. RC1 is Reaction Center 1 which includes green sulfur bacteria and heliobacteria while Reaction Center 2 includes purple and green filamentous bacteria. Variables such as P480 indicate the long wavelength absorption maxima for the electron donor (P). Other abbreviations include Chl which indicates Chlorophyll, BChl indicate bacteriophyll. Image by Govindjee and Dmitriy Shevela (2011). [ 6 ] Licensed under the Creative Commons Attribution 3.0 Unported license.