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Unformatted text preview: mRNA- 5 Cap o Structure 7-methyl guanylate 3 phosphates 2 ribose with and OH at the 2 or 3 carbon 5 to 5 linkage btwn the ribose-phosphate-ribose o Mechanism for Capping RNA triphosphatase removes 1 phosphate from 5 end of RNA Guanylyltransferase Adds GMP to 5 phosphate Forms 5-5 linkages S-adenosyl methionine (AdoMet) Adds methyl to methyl guanylate o Function Makes it easier for splicing Transportation out of the nucleus Prevents degrading of mRNA Enhances the translatability of mRNA- Poly (A) Tail o Mechanism CstF (cleavage stimulation factor)-binds to GU/U region and facilitates cutting CPSF (cleavage polyA specificity factor)-binds to the AAUAAA region facilitates cutting PAP (polyA polymerase protein) CF I and II (Cleavage factor)-binds to cutting site CstF and CPSF work together to cut CTD of RNA poly II helps stimuate the cutting After cleavage CF I and II fall off and CstF PolyA polymerase and CPSF start PolyA synthesis till 10nt oligos long PAB II (polyA binding protein) elongates till 250 nt long o Function protects RNA from degradation enhances translatability of RNA - Splicing o Differential splicing Truncation Alternative exons o Taking out the intron (noncoding regions of DNA to produce RNA) o Gives different expressions from the same sequence of DNA o There are highly conservative regions in the pre-mRNA o At the 5 end of the intron there is pGU and at the 3 end there is AGp o In the middle of the intron there is a conserved A. o Mechanism 2 sequential transesterificantion reactions The OH of the A attacks the phosphate of the pGU at the phospodiester bond, separating them. Then the remaining OH at the 3 end attacks the AGp phosphate also separating the bond The two ends of the intron as linked together as a result. snRNA splices the pre-mRNA 6 U-rich RNA in the nuclei U1 and U2 U1 - binds to the 5 of the intron and the 3 of the exon on the conservative regions - 3 major proteins sm U1-A specific to U 70k U2 binds to the 3 on the intron U2 binds but doesnt have the making U to the A that eventually sticks out to attack the phosphodiester bond of the pGU of the 5 of the intron Splicesomes mRNA snRNA proteins catalyzes splicing action DNA Replication - Semiconservative replications o Use one strand as the template o DNA unzips o Meselson and Stahl exp Use heavy N 15 Observed replication Originals all N15 Replicated will have various amounts of N14 depending on conservative/semiconservative/fragments Centrifuge in a CsCl density gradient to determine various density....
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- Winter '06