MadSci Network: Evolution |
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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