There Was an RNA World, What Preceded It

The logical problem in imagining a prehiotic DNA/protein world is determining which came first the genetic library to specify proteins or the enzymes that catalyze the formation of DNA RNA world appears to solve some of this dilemma since RNA is both informational and catalytic. However, RNA is very reactive and does not appear to be capable of synthesis and survival under prebiotic conditions. 

There is simply no firm fossil evidence identifying primordial biochemistry. In the evolution of flowering plants, the fossil record is rather 

The use of animal antibodies to detect antigens is highly effective but it involves the use of animals, complex separations, and has a variety of limitations. Starting around 1990 a new method for detection and separation of substances, including amino acids, proteins, and pharmaceuticals, was developed based on synthetic nucleic acids termed aptomers aptos = to fit ). Aptomers are DNA or RNA molecules that bind with high specificity to certain molecules. Their application depends upon many principles described earlier in this book chromatography, combinatorial chemistry, and the polymerase chain reaction (PCR) technique. 

The formation of aptamers rests upon a technique termed SELEX (systematic evolution of ligands by exponential enrichment). It involves the synthesis of a DNA molecule with constant sections at both ends and a randomly variable segment of nucleotides in the middle. A variable segment as short as 10 nucleotides has a combinatorial library of 4 ° or about 10 different sequences a variable sequence of 30 nucleotides generates a combinatorial library of 4 or about 10 different sequences. The DNA mixture so synthesized is then enzymatically transcribed to a combinatorial RNA library. This mixture is applied to a chromatography column in which the substance of interest (e.g., amino acid, protein, drug) is bound. RNA molecules in the combinatorial library that do not bind with the target compound are simply washed out of the column. 

The few selected RNA molecules are then eluted by a solution containing the molecule of interest. Active RNA aptamers are used as templates for enzymatic synthesis of the corresponding DNA. The resulting samples of DNA are then amplified using PCR and sequenced so that the specific synthetic DNA or RNA aptamer may be obtained in high yield. 

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