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Biological Sciences
BIOL 3090
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1What are minisatellite sequences and how are they used to fingerprint individuals Fig 67 How do minisatellites change in number in the genomeMinisatellitessimple sequence DNA in 15kb regions made up of 2050 repeat units each containing 14100 base pairsThese polymorphisms difference in sequence between individuals of same species can be used for DNA fingerprintingMinisatellites change in number in the genomes due to unequal crossing over in meiosis2Transposons versus viral retrotransposons Figs 68 610 612 613 Transposons Cut and pasteRetrotransposons Copy and pasteLeftward retroviral LTR functions as a promoter that directs hostcell RNA pol to initiate transcription at R sequenceAfter transcription the RNA sequence of rightward LTR directs hostcell RNAprocessing enzymes to cleave the primary transcript and add a polyA tail Resulting retroviral RNA genome lacks complete LTR and is packaged into budding virionAfter a retrovirus infects cell reverse transcription takes place in cytosol dsDNA with an LTR at each end is then transported to nucleus and inserted into hostcell genome by integrases integrases are closely related to transposases encoded by DNA transposonsLTR retrotransposons encode reverse transcriptase and integraseThe LTRs are regenerated by some fuckall super complex mechanism that I dont want to learn3LINEs and SINEs Figs 616 617 LINEs and SINEs are the two classes of nonLTR RetrotransposonsLINEs Long interspersed elements 6000bp long 21 of DNAAs with almost all mobile elements LINEs usuall are flanked by short direct repeats ORF1 encodes an RNAbinding protein ORF2 encodes a reverse transcriptase w DNA endonuclease activityFig617 After synthesis of ORF1 and ORF2 in cytosol complex of LINE RNA multiple copies of ORF1 and one copy of ORF2 bound to the PolyA tail moves into the nucleus1 ORF2 makes staggered nicks in chromosomal DNA on either side of any accessible AT rich sequence2 Reverse transcription of LINE RNA by ORF2 is primed by the single stranded Trich sequence generated by the nick in the bottom strand which hybridizes to the polyA tail35 ORF2 reverse transcribes the LINE RNA and then continues this new DNA strand switching to the singlestranded region of the upper chromosomal strand as a template6 Cellular enzymes hydrolyze the RNA and extend the 3 end of the chromosomal DNA top strand replacing the LINE RNA strand with DNA7 The 5 and 3 ends of the DNA are ligated completing the insertionNote DNA form of an LTR retrotransposon is synthesized from RNA in cytosol then transported into nucleus where it is integrated into chromosome by retrotransposon integrase DNA of nonLTR retrotransposon is synthesized in the nucleus There is no need for an integraseSide note LINEs are usually truncated at 5 end generally not further transposed bc they lack promoter also most contain stop codons Result is only 001 of LINEs are full length w intact open reading framesSINEs Short interspersed elements 300bp long One major class Alu 10 of genomeDo not encode protein Transcribed by RNA Pol IIIMost likely the ORF1 and ORF2 proteins from LINEs mediate reverse transcription and integration of SINEsBasically parasites of LINEsAlu units likely evolved from 7SL RNA a cytosolic RNA in a ribonucleoprotein complex called the signal recognition particle4Exon shuffling Figs 618 619
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