Microbes and Metabolism - Environmental Biotechnology: Theory and Application - page 36

derived from two molecules of the amino acid glycine. During this mitochon-
drial process, one molecule of molecular oxygen is consumed in the production
of carbon dioxide and the amino acid, serine. The superfluous amino group from
the second glycine molecule is released as ammonia. The glycine molecules were
derived from phosphoglycolate, the metabolically useless product of photorespira-
tion. This subject is very important with regard to plant breeding and development
and so is discussed in some detail alongside the related subject of photosynthesis.
Photosynthesis and the Basis of Phytotechnology
The sun is the biosphere's ultimate source of energy and photosynthesis is the
only means there is on this planet to trap incident sunlight and convert it into
chemical energy available to biological processes. Thus, with very rare excep-
tions, organisms which do not photosynthesise, which is the majority, are totally
dependent on those which do. With this introduction it is hardly surprising to find
a description of this process in a topic which specifically addresses the capabili-
ties of biological organisms and their interplay. Leafy plants obviously feature in
this section but so too do photosynthetic eukaryotic microorganisms and bacte-
ria. A knowledge of this vital process is essential to appreciating the role which
photosynthesising organisms play in the environment, their limitations and the
strengths upon which biotechnology can capitalise.
This process is used to drive all the biochemical synthesis and degradation reac-
tions occurring in the cell in addition to various other energy requiring processes
such as the movement and transport of molecules across membranes. Energy is
finally dissipated as heat, and entropy rises in accordance with the Laws of Ther-
modynamics. Any interference with the flow from the sun either by reducing the
ability of the energy to penetrate the atmosphere, or by reducing the total photo-
synthetic capacity of the planet, has dramatic consequences to all forms of life.
Conversely, too intense a radiation from the sun resulting from thinning of the
ozone layer runs the risk of damaging the photosynthetic machinery. This can be
compensated for by the organism acquiring pigments to absorb harmful radiation,
but it requires time for such an evolutionary adjustment to take place.
It is noteworthy that the bulk of photosynthesis is performed by unicellular
organisms, such as photosynthetic algae, rather than the macrophytes as might
reasonably be supposed. Photosynthesis occurs in two parts; the first is the trap-
ping of light with associated reduction of NADP + and ATP synthesis, and the
second is the fixing of carbon dioxide by its incorporation into a carbohydrate
molecule. This is most commonly a hexose sugar, and typically glucose, the
synthesis of which utilises the NADPH and ATP produced in the light depen-
dent part 1. The processes of carbohydrate synthesis occurring in the second part
are described as the dark reactions, so called because they may proceed in the
dark after a period of illumination to activate part 1. The sugar produced during
these dark reactions will then be utilised by the cell, transferred to another cell
or ingested by a larger organism and eventually catabolised to carbon dioxide