This paper is an analysis conducted on Nucleic Acids through a variety of tests specifically, Dische, Murexide, Wheeler-Johnson and Phosphate Tests in order to exemplify structural features of nucleic acids as well as identify the principle involved in each chemical test. Different procedures and different test compounds were applied, and results were noted as for changes in colors of precipitates or solutions. For Dische Test, light blue was obtained for RNA and dark violet for DNA. For Murexide Test, a yellow layer was obtained with a mixture of red color and eventually became yellow or orange after addition of warm water. For John-Wheeler Test, a violet precipitate was obtained and lastly for Phosphate Test, a yellow precipitate was obtained.
Keywords: Nucleic Acids, Dische Test, Murexide Test, Phosphate Test, Wheeler-Johnson Test1.
The experiment solely revolved on the identification of the different structural features that make up the complex structure of nucleic acids as well as its characterization through specific chemical tests namely Dische Test, Murexide Test, Wheeler-Johnson Test and Phosphate Test. Upon performance of the tests mentioned, the principles involved were identified and stated based on the results obtained from the experiment.
2. MethodologyMaterials such as water bath, test tubes, evaporating dish, test compounds and reagents were gathered and prepared.
In Dische Test, ten (10) drops of test compound and Diphenylamine wasplaced in a test tube and heated in boiling water bath for ten minutes. Color change on the solution was noted.
In Murexide Test, ten(10) drops of Guanidine was placed in a test tube. Concentrated Nitric Acid(HNO3) was added to the test compound and then brought to water bath to dry until a solid mixture is obtained. Once the mixture dried up, ten(10) drops of Potassium Hydroxide(KOH) was used to wet the reagent and then later on put to boiling water bath again to dry. After addition of KOH, color change was noted and this time, water was added to wet the mixture and put to boiling water bath again to dry. Any color change to the precipitate was noted.
For Wheeler-Johnson Test, ten(10) drops of Barium Hyrdroxide[Ba(OH)2] and Bromine Water placed in a test tube and once the mixture turned red, it was brought to boiling water bath to expel excess Bromine. More than ten(10) drops of Barium Hyrdroxide[Ba(OH)2] was added in excess and color change of the precipitate was noted.
In Phosphate Test, twenty(20) drops of test compounds were placed in a porcelain crucible and two(2) drops of Potassium Nitrate(KNO3) plus ½ spatula fusion mixture of Sodium Carbonate(NA2CO3) was added to the test compound. Mixture was heated using a Bunsen burner until the mixture turned into gray or white. After cooling the mixture, 5 mL of distilled water was added to the reagent and was transferred to a test tube acidified by ten(10) drops of concentrated Nitric Acid(HNO3). Litmus paper was then used to check for acidity and twenty(20) drops of ammonium molybdate solution was added to the reagent & warmed in water bath. Once warmed, the mixture was allowed to stand for ten minutes and formation as well as color of the precipitate was noted.
After performing all the tests needed, results were tabulated and analyzed accordingly.
3. Results and Discussion
Dische Test clearly indicates that DNA can be identified chemically with the Dische diphenylamine test. DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are aldehydes, which reacts with the compound, diphenylamine, to produce a blue-colored compound. A positive test for DNA is indicated by a blue color change. This procedure involves chemical hydrolysis of DNA: when heated in acid, the reaction requires a deoxyribose sugar and therefore is specific for DNA. Under these conditions, the 2-deoxyribose is converted to w-hydroxylevulinyl. This resulted to a blue solution indicating the presence of protein in DNA.
Murexide Test on the other hand gave out a yellow precipitate which indicates the presence of uric acid visible in the Guanine samples. It is a double-ringed, crystalline organic base, C5H4N4, not known to occur naturally, and is a form of uric acid heterocyclic in nature.
In the Wheeler-Johnson Test, the evidence for a positive result is a violet solution and this clearly shows the concise result of the experiment performed. Cytosine was used in the test which is a Pyrimidine derivative heterocyclic in nature.
Phosphate Test gave out a yellow result for the precipitate which simply means that a phosphodiester bond exists between DNA and RNA between the 3′ Carbon atom and the 5′ Carbon of the ribose sugar.
From the experiment, it is therefore meant that through specific tests, it is possible to characterize structural features of nucleic acid whether it be a helix, string loop or miniband. That certain compound complements the test to be performed and will result to a concise data if performed correctly. That DNA differs from RNA in the sense that only Uracil is found in RNA and Thymine is exclusively located in the DNA though Adenine, Guanine, and Cytosine are both found on DNA & RNA..
Pratt, Charlotte W. Title Essential biochemistry / Charlotte W. Pratt. Publication info. New York: Wiley, 2004.
What is DNA? : A biology adventure / written by Transnational College of LEX translated by Alan Gleason. Publication info. Boston: Language Research Foundation, c2003.