DNA Evolution
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<b> Retroviruses </b>store their genetic information on RNA rather than DNA, upon entering a cell, a retrovirus copies its RNA genome into DNA -- A process known as reverse transcription. A retrovirus only becomes endogenous if it inserts into a cell whose chromosomes will be inherited by the next generation e.g. sperm or ova.
 
The <b>RNA world </b>refers to the self-replicating ribonucleic acid (RNA) molecules that were precursors to all current life on Earth. It is generally accepted that current life on Earth descends from an RNA world, although RNA-based life may not have been the first life to exist.
 
The <b>RNA world hypothesis</b>, if true, has important implications for the definition of life. For most of the time that followed Watson and Crick's elucidation of DNA structure in 1953, life was largely defined in terms of DNA and proteins: DNA and proteins seemed the dominant macromolecules in the living cell, with RNA only aiding in creating proteins from the DNA blueprint.
 
<b>The RNA world hypothesis places RNA at center-stage when life originated.</b> This has been accompanied by many studies in the last ten years that demonstrate important aspects of RNA function not previously known—and supports the idea of a critical role for RNA in the mechanisms of life. The RNA world hypothesis is supported by the observations that ribosomes are ribozymes: the catalytic site is composed of RNA, and proteins hold no major structural role and are of peripheral functional importance. This was confirmed with the deciphering of the 3-dimensional structure of the ribosome in 2001. Specifically, peptide bond formation, the reaction that binds amino acids together into proteins, is now known to be catalyzed by an adenine residue in the rRNA.
 
Other interesting discoveries demonstrate a role for RNA beyond a simple message or transfer molecule. These include the importance of small nuclear ribonucleoproteins (snRNPs) in the processing of pre-mRNA and RNA editing, RNA interference (RNAi), and reverse transcription from RNA in eukaryotes in the maintenance of telomeres in the telomerase reaction.
 
 
 
 
 
 
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