Chemical evolution bacteria

However, before bacteria could evolve, the fundamental chemistry of life needed to be established. For this we need to turn back the clock to around 4.5 - 4.1 billion years ago where the earth s crust has cooled and solidified and the oceans and atmosphere begin to form. It is speculated that iron-sulfide synthesis along deep oceanic platelets may have lead to the synthesis of the first RNA and self-replicating molecules. Exactly how this chemical evolution came about remains an open question. It is possible that RNA may have used clays and similar self-replicating materials as substrates. Eventually, this... 

The influence of plant sterols on the phase properties of phospholipid bilayers has been studied by differential scanning calorimetry and X-ray diffraction [206]. It is interesting that the phase transition of dipalmitoylglycerophosphocholine was eliminated by plant sterols at a concentration of about 33 mole%, as found for cholesterol in animal cell membranes. However, less effective modulation of lipid bilayer permeability by plant sterols as compared with cholesterol has been reported. The molecular evolution of biomembranes has received some consideration [207-209]. In his speculation on the evolution of sterols, Bloch [207] has suggested that in the prebiotic atmosphere chemical evolution of the sterol pathway if it did indeed occur, must have stopped at the stage of squalene because of lack of molecular oxygen, an obligatory electron acceptor in the biosynthetic pathway of sterols . Thus, cholesterol is absent from anaerobic bacteria (procaryotes). 

Thiamine diphosphate is a particularly interesting substance because it illustrates a chemical evolution from lactic acid bacteria to yeasts and then to higher animals. It converts pyruvic acid, which is an a-keto-acid, into the equivalent of a 3-keto-acid (with C=N instead of C=0), which can then lose CO2 by decarboxylation. We know that the hydrogen atom next to nitrogen in the thiazole ring is acidic and easily removed because if we shake thiamine with D2O, we get rapid exchange of that atom (Figure 2.11). 

Experimental information on the early evolution and the beginning of live is extremely difficult to obtain only the arrival of microbial genomics has allowed to reliably retrace subsequent developments. The earth was formed about 4.5 10 years ago. The earliest traces of primitive cells occurred possibly as early as 3.5 10 years ago (Schopf 2006). Nevertheless, this leaves several hundred million years for the actual chemical evolution. The evolution of cells (Woese 2002), however, has taken the major portion of the remaining time. The step from microorganisms (bacteria) to higher live forms occurred much later— less than 1 10 years ago. Even tough the very early steps towards cellular Uve are still in the dark, it is very likely that autocatalytic reactions in conjunction with steady state bifurcations, of which we... 

Before we describe the chemistry of the compartments involved, note that like prokaryotes, a number of oxidative enzymes are found in the cytoplasm but they do not release damaging chemicals (see Section 6.10). We also observed that such kinds of kinetic compartments are not enclosed by physical limitations such as membranes. We have also mentioned that increased size itself makes for kinetic compartments if diffusion is restricted. In this section, we see many additional advantages of eukaryotes from those given in Section 7.4. How deceptive it can be to use just the DNA, the all-embracing proteome, metabolome or metallome in discussing evolution without the recognition of the thermodynamic importance of compartments and their concentrations These data could be useful both here and in simpler studies of single-compartment bacteria even in the analysis of species but not much information is available. 

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