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Trying to provide all necessary information about IMMUNITY and IMMUNE SYSTEM

RNA-The first form of life|Ribo Nucliec Acid

Posted by Mumtaz khan Wednesday, 18 January 2012

          Although RNA,like DNA,can store hereditary information,it is not as good a starch house of the same as DNA.Unlike DNA,RNA is essential in decoding stored information,self-replication of DNA is well known,but it is mediated by the enzyme-DNA polymerase.In other words,DNA cannot replicate without the help of well-defined protein catalysts.But there are instances of RNA molecules that self-catalyse with sequence-specific hydrolysis and transesterification reactions of RNA substrates.This findings justifies the role of RNA catalysts in the origin of life..RNA catalysis may have been crucial at any early stage in biochemical evolution.The RNA was the original self-replicating molecule that delegated to DNA the storage information capacity and to polypeptides the controllable activities.A consequence of the co-operation of the 3 kinds of macro molecules(RNA,DNA,and Protein.)is the evolution of the efficiency of self-replicating entities,the living cells.

         Crick(1968)proposed that the first form of life were essentially RNA machines.
Thus,life appeared when the period of chemical evolution was almost over atleast 4 billion years ago.It was the first stage of organic evolution.It was a RNA world.Since the RNA molecules used to adapt to new niches of enironment.The notion that life began from RNA remains very attractive.

         The genetic system explored by Hershey and chase was a phage-a bacterial virus(which had DNA as genetic material).
A virus particle by itself is essentially just a package of genes(can be DNA or even RNA).It has no life of its own,no metabolic activity,it is inert.But when the virus infects a host cell,it seems to come to life.Suddenly the host cell begin making viral proteins outside,but lifelike agents inside hosts,viruses resist classification.Some scientists refer to them as ''livings'' or even ''organisms''.We prefer a label that although more cumbersome is also more descriptive of a virus's less than living status;thus we will call a virus a genetic ''system''.The term applies to any entity-be it a true organism,a virus or even a bare circle of plant-infectinf RNA called a VIROID-that contains genes capable of replicating.
Most genetic systemstudied to date contain genes made of DNA.But some viruses including several phages(TMV,influenza virus,Polio virus,Rous sarcoma Virus(RSv),AIDs virus etc.)Plant nad animal viruses and all viriods have RNA genes.Sometimes viral RNA genes are double stranded but usually they are single stranded.


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