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Localization of Nucleic Acids

DNA can be located in the cell by the Feulgen reaction, by the enzyme deoxyribonuclease and by ultra-violet light.

(1) The Feulgen reaction. In 1912 Feulgen discovered that when DNA is hydrolysed with warm Schiff’s reagent it becomes reddish purple in colour. Hydrolysis permits Schiff’s reagent to react with aldehyde groups in the sugar deoxyribose. By measuring the amount of light transmitted through the chromosome, quantitative estimation of DNA can be made.

(2) Deoxyribonuclease.
  DNA can be removed by the enzyme deoxyribonuclease. (RNA can be removed by ribonuclease). After removal of DNA the nucleus does not give the Feulgen reaction.

(3) Ultra-violet absorption. The visible spectrum of light extends from 6,500A to 4,500A. Wavelengths shorter than 4,500 are called ultra-violet. Nucleic acids absorb ultra-violet light at a wave-length of 2,600A. By this method it is possible to locate DNA without staining the chromosomes. Caspersson and others have used this method to measure the nucleic acid content of nuclei.

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