Microbes and Metabolism - Environmental Biotechnology: Theory and Application - page 39

Figure2.10 Oxygenicphotosynthesis,photorespirationandtheHatch-Slackpathway
finally NADP + , which also collects a hydrogen atom to complete the reduction
to NADPH. Both the cyclic and the non-cyclic pathways produce a proton gradi-
ent which drives the synthesis of ATP, but only the cyclic route has the facility of
producing NADPH. A combination of cyclic and non-cyclic pathways are used
by the organism to produce the required amounts of NADPH and ATP used in
the dark reactions for the synthesis of carbohydrate. So far the description has
been of photosynthesis in eukaryotes and cyanobacteria.
Photosystems in purple and green bacteria
Looking at the general equation for the chemical reactions in photosynthe-
sis shown in Figure 2.11, it may be seen that water is the electron donor
during oxygenic photosynthesis while several molecules may play the same
role in anoxygenic systems. Suitable molecules are listed in the figure, from
which several interesting observations may be made. If the electron donor is