Proteins, introduction function, mechanisms

Fig. 1. Schematics of evolutionary mechanisms of domain swapping in nature. Multifunctional proteins arise from the fusion of the genes coding for individual enzymes. Often the individual domains of multifunctional proteins catalyze successive steps in metabolic pathways. In tandem duplication, a gene is duplicated and the 3 end of one copy is fused in-frame to the 5 end of the second copy. In domain recruitment, a functional unit (whole gene or gene fragment) from one gene is either inserted within or fused to an end of a second gene. Circular permuted genes are believed to arise via tandem duplication followed by introduction of new start and stop codons (Ponting el at, 1995).

A clear introduction to the mechanisms of hormonal function and disruption has been provided by Eubanks (1997) and is summarized here. Hormones are regulatory molecules produced by the endocrine system that fit precisely to proteins called receptors. This interaction is very precise and constitutes the reception of a chemical message by a particular cell. Upon reception of the message, dramatic changes can occur in the cell although extremely small amounts of the hormone may be present. The reaction to the interaction of the hormone and receptor are specific to the type of cell... 

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