GCD 3022 1st Edition Lecture 24 Outline of Last Lecture I Overview of Epigenetics a Epigenetics b Epigenetic inheritance c Epigenetic regulation II Cis and trans epigenetic changes a Cis epigenetic changes b Trans epigenetic changes III Epigenetics and development a Process of development b Epigenetic regulation IV Genomic imprinting a Igf2 gene and methylation b CTC binding factor V Development of specific cell types a Embryonic development b Polycomb group PcG c Inhibition of transcription VI Regulation of RNA processing These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute a Alternative splicing b Alpha tropomyosin c Splicing factors VII mRNA stability a regulation of stability b factors that affect stability i length of polyA tail ii destabilizing elements c RNA interference i miRNA ii double stranded RNAs Outline of Current Lecture I RNA interference a Definition b Process II Genetic Imprinting a Igf2 gene b ICR mutation III mRNA degradation a mRNA half life b advantages and disadvantages of short half life c advantages and disadvantages of long half life IV Alternative splicing a Example b Explanation Current Lecture I RNA interference a Definition also known as RNAi this mechanism of RNA modification involves a double stranded RNA known as micro RNA or miRNA This type of RNA does not code for proteins but instead hybridizes with mRNA which has a direct effect gene expression b Process RNAi leads to silencing of gene expression by using the double stranded miRNAs to pair with mRNA which prevents the gene from being expressed II Genetic Imprinting method of epigenetic inheritance in which one parental allele is inactivated during gametogenesis formation of egg or sperm a Igf2 gene common example of genetic imprinting in which the male s sperm is methylated during spermatogenesis and the female s eggs are not methylated This results in the male s Igf2 gene being active and the female s inactive b ICR mutation a mutation to the imprinting control region in the female s DNA will probably not change whether the Igf2 gene is expressed or not Since the female s DNA is not methylated CTC factors bind to the ICR and DMR and these factors cause the formation of a loop in the DNA which renders it inactive With the removal of the ICR only one CTC could bind to the DMR but this may still be enough to inactivate the gene III mRNA degradation occurs as the mRNA ages and the polyA tail shortens a mRNA half life the unit of time that determines how long an mRNA will last This could be hours days or even months depending on the mRNA molecule b Advantages and disadvantages of short half life an advantage of a short half life are that it allows more adaptability in regulation of protein production and a disadvantage is that it is inefficient at making mRNA consistently c Advantages and disadvantages of long half life an advantage of a long half life might is that they don t have to remake mRNA constantly and a disadvantage is that it might end up expressing a protein that is not necessary for the cell IV Alternative splicing splicing of pre mRNA may produce different codons depending on how it is spliced and which splicing factors act on it a Example a gene has four exons and some cell types of the mature mRNA contain all four exons while others are missing exon 3 It is suspected that the cells that lack exon 3 express a splicing repressor Determine which splice site this repressor acts on b Explanation the repressor acts on the 3 splice site of the third intron The spliceosome can then assemble normally at the 5 splice site of intron 3 but does not recognize the 3 site so it splices both the intron and the exon removing exon 3 from the molecule The spliceosome then continues splicing the rest of the molecule leaving exons 1 2 and 4
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