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BIOL 3110
Peter Cheung

Sept 24, 2009 E. Coli -In E. Coli the rRNA makes up approximately 80% of all the RNA present and the tRNA is about 15% and the mRNA/sRNA is about 5%. -Due to the relative small size and amount of mRNA it was quite difficult to discover the existence of mRNA; mRNA is quite unstable, one of the reasons for this is that it is a useful tool for gene regulation (control the level of initiation and transcription, the rate of turnover also causes the transcript to be quickly degraded). This is not always the case with the higher eukaryotes that have can have long lived mRNA Subunits of RNA (fig.1.19 Singer & Burk) -RNA subunits are linked together in the same manner as DNA (5’-3’ phosphate bonds) the main difference is that there is a 2’ OH that allows it to have catalytic activity; the OH-group also means that the molecule cannot be degraded by pH, but makes it sensitive to hydrolysis of the phosphate bond by alkaline substances. -Modifications that can occur are: 1) methyl, thiol, and hydrogen substitutions in the bases 2) methylation at the 2’ C in the sugar 3) altered linkage between the base and the sugar groups -Many of the alterations listed above are vital to the function of tRNA. RNA Structure -Dystrophin is the missing protein in individuals with DMS, the primary structure for this molecule is approximately 2 x 10 nt in size; to date this is one of the largest molecular transcript found. ( half the length of Ecoli genome) -Most of the RNA molecule have secondary structures and it can be quite extensive in complexity (hairpin, double hairpin, multi-branched structure) -One of the unique features of RNA is that it can have non-conventional base pairing because the sugar phosphate backbone is flexible (“non Watson & Crick pairing” such as GU, GA, AC, AA, GG). -When RNA forms a double strand structure whether by nature or due to secondary interactions (RNA:RNA) it will resemble the A form of DNA. -Refer to fig 1.22 Singer & Bu
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