Metabolism first, theory

The common ancestor of life was probably a chemoautotrophic hyperthermophilic anaerobe. This metabolism first theory assumes that life started with catalytic metal sulfide surface/compartments in a hydro thermal-vent setting in the Hadean... 

SMALL-MOLECULE ( METABOLISM FIRST ) THEORIES OF LIFE S ORIGIN... 

The sudden appearance on Earth of a system capable of both metabolism and replication is too unlikely to be taken seriously. All reasonable theories on the origin of life assume therefore that chemical evolution started from systems that could perform only one of those functions. Hence the great schism between metabolism-first theories (Oparin s paradigm) and replication-first scenarios... 

The wide gap between the two opposing theories, replication first and metabolism first , was analysed by Pross from the Ben Gurion University of the Negev (Israel). Pross concludes that replication came first He is convinced that a causality between the two theories can only be established if it is assumed that the replication-first thesis is correct. His analysis also shows that more of the experimental results and theoretical rationales favour the replication thesis. The author finds his assumption justified that life processes are strongly kinetically controlled and that the development of metabolic pathways can only be understood if life is considered as a manifestation of replicative chemistry (Pross, 2004). 

From the observation that tics were exacerbated by stress, and because cerebrospinal fluid flndings suggested possible alterations in central nervous system catecholamine metabolism, Cohen and colleagues (1979) used clonidine in the treatment of TS in what was among the first theory-based treatments for the disorder. 

That view of the origin of life has commonly been called metabolism first the absence of a genetic polymer has been equated with the lack of any mechanism for heredity. As we have seen, replicator theories center on the spontaneous formation of large, information-bearing organic polymers endowed with the ability to copy themselves. The hereditary information carried in the sequence of such a polymer is called a genome. 

The concept of postchemical evolution, in conclusion, allows us to realise that there is another important dichotomy in the origin of life field. In addition to the distinction between metabolism-first and replication-first theories, it is necessary to distinguish between theories of chemical evolution and theories of postchemical evolution. 

Up until the origin of RNA molecules, Dyson describes the logical consequences of the initial hypotheses, and his scheme is therefore a coherent theory of chemical evolution. But the mathematical model does not say anything about the subsequent integration of RNAs and hosts, and on this point Dyson resorts to a supplementary conjecture. He proposes that primitive RNAs invaded their metabolic hosts, and used them for their own replication, like viruses do, which is exactly Haldane s hypothesis. Dyson concludes therefore that, after Oparin s metabolism stage, came Haldane s replication stage, and his final scheme becomes metabolism first, replication second . That RNAs... 

The results obtained appeared quite promising, but the real sensation was the detection of pyruvate, the salt of 2-oxopropanoic acid (pyruvic acid), which is one of the most important substances in contemporary metabolism. Pyruvic acid was first obtained in 1835 by Berzelius from dry distillation of tartaric acid. The labile pyruvate was detected in a reaction mixture containing pure FeS, 1-nonanethiol and formic acid, using simulated hydrothermal conditions (523 K, 200 MPa). The pyruvate yield, 0.7%, was certainly not overwhelming, but still remarkable under the extreme conditions used, and its formation supports Wachtershauser s theory. Cody concludes from these results that life first evolved in a metabolic system prior to the development of replication processes. 

While uncontrolled topical delivery of proteins and peptides for local application such as open wound healing is easily achieved, it is much more challenging to use transdermal delivery systems to deliver protein across intact skin. In theory, transdermal delivery could provide constant drug release for days, avoids first-pass metabolism, and could allow drug effects to be rapidly terminated by simply removing... 

The lipostat theory postulates a mechanism that inhibits eating behavior and increases energy consumption whenever body weight exceeds a certain value (the set point) the inhibition is relieved when body weight drops below the set point (Fig. 23-30). This theory predicts that a feedback signal originating in adipose tissue influences the brain centers that control eating behavior and activity (metabolic and motor). The first such factor, leptin, was discovered in 1994, and several others are now known. 

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