Index >> Microorganisms Types >> DNA Base Composition

DNA Base Composition - Although DNA base composition may be determined chemically (hydrolysing DNA sample and separating the free bases) it can be determined more easily by physical methods that are now mostly used.

The melting temperature or buoyant density of DNA (i.e. the temperature at which it becomes denatured, by breakage of the hydrogen bonds holding the two strands together) is directly related to G+C content. Strand separation is accompanied by marked increase in absorbance at 260 nm, . the absorption maximum of DNA. When a DNA sample is gradually heated, the absorbance increases as the hydrogen bonds are broken and reaches a plateau at a temperature at which the DNA has all become single stranded

Each bacterial species accordingly has DNA with a characteristic mean G+C content which can be considered one of its important specific characters.

It has been observed in this approach that a substantial divergence between two organisms with respect to mean DNA base composition reflects a large number of individual differences between the specific base sequences of their respective DNAs. It is very important as the major genetic divergence reflects a wide evolutionary separation.

However this may not be true. Since two organisms with similar mean DNA base composition may differ greatly in genetic constitution. This is true for plants and animals. However this technique proved useful for microbes.