RNA AS GENETIC MATERIAL

PROOF AND EXPERIMENTS FOR RNA AS GENETIC MATERIAL

1. RNA AS GENETIC MATERIAL

2. RNA Ribonucleic acid  ( RNA ) is a polymeric molecule essential in various biological roles in coding, decoding,  regulation and  expression of   genes

3. SOME ORGANISMS HAVE RNA AS GENETIC MATERIAL : Some Viruses have RNA as Genetic Material. RNA Virus ( Ribo Virus ) may have ssRNA or dsRNA enveloped by Protein Coat . H uman diseases caused by RNA viruses include SARS, Influenza ,Hepatitis C, Measles, Mumps and Rabies Rous Sarcoma Virus (causing cancer ) and HIV ( causing AIDS ) both are Retrovirus using Reverse Transcription for DNA synthesis in host cell

4. EXAMPLES OF PLANT RNA VIRUSES Tobacco Mosaic Virus (TMV ) was crystallized by Stanley (1935 ) for the first time TMV causes Tobacco mosaic disease . TMV can also cause disease in Tomato, Pepper, Snapdragon and Marigold . Papaya Ring Spot virus (PRV) Potato Leaf Roll Virus (PLRV)

5. RNA VIRUSES TMV HIV HEPATITES C VIRUS

6. EVIDENCE IN FAVOUR OF RNA AS GENETIC MATERIAL : The first evidence that RNA also has the capacity to carry genetic information came from experiments conducted with  tobacco mosaic virus (TMV).  

7. This virus does not contain any DNA, and is composed of RNA (6%) surrounded by a hollow cylinder of protein subunits.

8. Experiments with tobacco mosaic virus (TMV) A Gierer and G Schramm ( 1956 ) when inoculated tobacco plants with Purified RNA isolated from TMV - Lesions appeared on leaves of healthy plant . The experiments conducted by  H . Fraenkel-Conrat  in California showing that RNA is the genetic material in this virus.

9. Techniques were first developed for separating TMV particles into RNA and proteins . Later by using RNA and proteins separately in tests for infectivity, it could be shown that RNA alone was able to cause infection. Such a property was not found in the protein fraction .

10.  Fraenkel-Conrat and Singer took two different strains of TMV and separated the RNAs from protein coats, reconstituted hybrid viruses by mixing the proteins of one strain with the RNA of the second strain, and vice versa .

11. . Reconstruction of virus, showing that reconstructed virus gives progeny which resembles the virus from which RNA was derived

12. Inoculated Hybrid TMV into healthy tobacco plant -Tobacco Mosaic disease appeared. TMV progeny isolated from diseased plant showed parental RNA only but not parental proteins. This provided evidence that RNA carries information for assembly of Virus particles and not proteins

13. RNA thus is the Genetic Material in TMV