Deoxyribonucleic acid exons

Deoxyribonucleic acid (tobacco clone lambda T-FLO 4 gene NFL2 exon 1 fragment) 950b, 2072a, 4249... 

Deoxyribonucleic acid (tobacco clone pTGF220 gene NFL1 exon 1 fragment) XXII-2 ... 

A key feature of the above equations is that the reactions in Equation (4.1a) are reversible, but those represented in Equation (4.1b) are irreversible. This represents the very significant means whereby synthesis of the gene, the poly(deoxyribonucleic acid) encoding for protein, is an irreversible process. Another important expense of energy is that only intermittent parts, called exons, of the DNA sequence (the gene) actually encode for protein. For the DNA that encodes elastin, less than 20% is exon, the remainder, called introns, does not encode for the protein. In addition, there is much junk DNA carried along during replication that appears to serve no useful purpose. 

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