Primeval cells

As already mentioned, the HGT principle has been known for many years however, until about 15 years ago, it was regarded as only a weak force in the evolutionary events involved in the development of primeval cells, whose organisation must have been very simple. They probably had a loose structure which could easily be modified by HGT processes. An important characteristic of Woese s model is the nature of the evolutionary process Woese assumes that cell design could be achieved only by the overall performance of HGT. It was the community as a whole,... 

Fig. 10.11 The modified tree of life still has the usual tree-like structure and also confirms that the eukaryotes originally took over mitochondria and chloroplasts from bacteria. It does, however, also show a network of links between the branches. The many interconnections indicate a frequent transfer of genes between unicellular organisms. The modified tree of life is not derived, as had previously been assumed, from a single cell (the hypothetical primeval cell ). Instead, the three main kingdoms are more likely to have developed from a community of primitive cells with different genomes (Doolittle, 2000)...

In recent years, the transitions from nonliving to living matter have been the subject of three seminars, bringing together theoreticians and experimentalists in the Los Alamos National Laboratory, in the Santa Fe Institute and in Dortmund. The biogenesis problem was expanded to the question, how can simple life forms be synthesised in the laboratory Artificial cells (sometimes called protocells) could be quite different from the cell types known today, or from primeval cells they might, for example, be orders of magnitude smaller than a bacterium. The seminars posed three questions for further work ... 

The primeval cell probably contained about 100 protein molecules, in contrast to the many millions of protein molecules in modern cells, and it certainly contained a variety of metal ions some of which fulfilled structural osmotic or catalytic roles. Magnesium would have been particularly good in this latter role since it is known to catalyse condensation reactions and to have been present in high concentration in primeval oceans (it is currently present in a concentration of 50 mmol dm in modern sea water). The close similarity of the ionic composition of many of our body fluids and those found in sea water strongly supports the view that life evolved in, or from, the oceans. 

We have already seen that around 70% of the human body is water and this should be no surprise since, following development of the primeval cells in the oceans, evolution has continued within an aqueous environment and exploited the unique properties of water to the best advantage to living systems. Water is the only naturally occurring inorganic liquid and is the only compound which occurs in nature in all three physical states of matter solid, liquid, and gas. The omnipotence of the roles of water in the human body may be seen by reference to Table 1.1. Water is used to provide bulk to the body and use is also made of its unusual chemical properties. 

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