eChapter Name: Nucleic Acid Based Disease Diagnosis
9789358875096
eBook Name: FISH AND SHELLFISH HEALTH MANAGEMENT
by Omkar Vijay Byadgi, Naveen Kumar B.T, Raj Reddy
Introduction
Nucleic acid based diagnosis is highly specific, sensitive and rapid method widely used in health management. The detection is mainly based on structure and sequence of bases of nucleic acid which are unique to an organism. In recent years, nucleic acid based diagnosis is becoming common and popular in fish and shell fish health management. Commonly employed nucleic acid based diagnosis are DNA hybridisation and Polymerase chain reaction (PCR).
Nucleic acids are made up of nitrogen bases. The primary sequence of bases in DNA or RNA have regions which are unique for a particular organism or gene. The sequence of DNA is composed of a series of four phosphorylated bases Adenine (A), thymidine (T), guanidine (G) and cytosine (C). Pairs of bases (A=T, or G=C) can form hydrogen bonds, which cause opposing strands of DNA to form a semi-stable bonding (hybridization or annealing) to one another. If the opposing strands of DNA match exactly, then the familiar double helix form of DNA results. In the following example, the opposing strands in (1) will form a double stranded, tightly bonded structure, and the DNA strands are described as complementary. In (2) the strands are non-complementary (opposing A=T and G=C base pairs do not line up) and the two strands will not bond.
DNA Hybridisation
The basic principle in DNA hybridization is that, if a strand of double helix of DNA is separated from its complement (by heat) it will bind (reanneal or hybridize) only to its complementary strand (or to a duplicate of its complementary strand). Two complementary RNA structure will hybridise in the same manner. Inaccurate and mismatched bindings will be unstable and fall apart.
The binding of one DNA strand to another is in some respect is analogous to binding of antigen and antibody. However, in the case of nucleic acid bindings, the precise molecular nature of binding (base pairing) is known and can be easily manipulated by choosing DNA strand of appropriate length and by incubating the strands in appropriate salt concentration, temperature. The stringency (faithfulness of the match) of hybridisation can be precisely defined and as a result coincidental cross reaction is virtually eliminated.