MadSci Network: Evolution
Query:

Re: Green Skin

Date: Thu Jul 9 13:32:28 1998
Posted By: Man Mohan, Grad student, Department, University of Delhi
Area of science: Evolution
ID: 898986265.Ev
Message:

Organisms of earth can be divided into autotrophic and
heterotrophic
organisms depending on their mode of nutrition.  Autotrophs are
those that can make their own food with the help of some processes
such as photosynthesis, carried out by green plants, algae,
cyanobacteria and some protists.  Heterotrophs are organisms that
can not make their own food and obtain food from sources made by
autotrophs.  These includes all consumers and saprophytes.

During evolution, organisms have adapted different modes of
nutrition, and in accordance to it they have developed structures
which carry out their food acquiring processes with maximum
efficiency.

Plants and other photosynthetic organisms have all the necessary
structures and chemical compounds required for the long and complex
process of photosynthesis. Following is a brief description of the
photosynthetic process and the apparatus found in plants.
Photosynthesizing cells contain special organelles, called
chloroplasts inside which there are many disc shaped structures
(granum), stacked one above the other.  All the necessary pigments
(chlorophyll and accessory pigments, carotenoids and xanthophylls)
are present in the grana membranes.  Chlorophylls and the accessory
pigments absorb light energy.  The absorbed energy is passed on to
the chlorophyll molecule which gets excited and releases two high
energy electrons.  This high energy electrons then passes through a
chain of electron acceptors.  They are ultimately accepted by
NADPH2, an energy rich molecule.  While flowing down the chain of
electron receptors, ATP, another energy rich molecule is also
synthesized.  This two energy rich molecules are then used in a
series of interdependent reactions (Calvin cycle) in which carbon
dioxide is used to synthesize starch (food).

Thus it is not only the chlorophyll molecule which synthesizes
starch, but it is the highly coordinated efforts of photosynthetic
apparatus, pigments and enzymes necessary for catalyzing the
reactions.

Engineering ourselves to have chloroplasts in skin cells will be
quite away from nature.  It has not only technical difficulties but
also raises ethical and moral dilemma's.

Genes for all the structures of the chloroplast will be quite large
and isolating them will not be practical.  Even if we isolate them,
getting them inserted in the human genome will be quite difficult. 
Getting them expressed in the cells, I think, would be impossible. 
With our present knowledge, functioning chloroplasts in humans or
in any other heterotroph,  is a totally wild dream.



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