GCD 3022 1st Edition Lecture 25Outline of Last Lecture I. RNA interferencea. Definitionb. ProcessII. Genetic Imprintinga. Igf2 geneb. ICR mutationIII. mRNA degradationa. mRNA half-lifeb. advantages and disadvantages of short half-lifec. advantages and disadvantages of long half-lifeIV. Alternative splicinga. Exampleb. ExplanationOutline of Current LectureI. Epigeneticsa. Epigenetics vs. classical geneticsb. Epigenetic gene regulationc. Targeted genesThese 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.d. Igf2 geneII. Splicing Regulationa. SR proteinsb. Advantage of alternative splicingc. Splicing repressor Example 1d. Splicing repressor Example 2e. Types of exonsIII. mRNA half lifea. Definitionb. AU-rich elementsIV. RNA interferencea. Mechanism b. Non-coding RNAc. miRNA hybridizationd. RNAs in RNA interferenceCurrent LectureI. Epigeneticsa. Epigenetics vs. classical geneticsi. Epigenetics is the study of changes in gene expression that occur via different methods than classical genetics. The big difference between epigenetics and classical genetics is that the changes in gene expression in epigenetics are reversible and do not change the DNA sequence. b. Epigenetic gene regulation: the processes that underlie epigenetic gene regulation are DNA methylation, covalent histone modifications, chromatin remodeling, and histone variants.c. Targeted genes: a gene can be targeted for epigenetic regulation via the binding of a transcription factor or non-coding RNA.d. Igf2 gene: the Igf2 gene follows a cis pattern of epigenetic regulation, which means that the activation of the gene is not passed on to other copies of the gene. The ICR and DMR sequences are the methylated sequences in the Igf2 gene, and these sequences are only methylated in spermatogenesis (male only). This results in the binding of CTC factors to the unmethylated ICR and DMR regions on the female’s gene, which inactivates the Igf2 gene. II. Splicing Regulationa. SR proteins: common splicing regulatorsb. Advantages of alternative splicing: one primary transcript can give rise to several different mRNAs, one primary transcript can give rise to several different proteins, and it allows cells to produce different versions of one protein that serve different but related functions. c. Splicing repressor Example 1: a pre-mRNA has 5 exons and a splicing repressor blocks the activity on the 3’ splice site of intron 3. Therefore exons 1,2,3 and 5 would be present in the mature mRNA and exon 5 would be skipped. d. Splicing repressor Example 2: another pre-mRNA contains 5 exons but the splicing repressor binds to the 5’ splice site of intron 3. This means that the mature mRNA would contain exons 1,2,3,4, and 5 as well as intron 3 because the splicing repressor missed the repressed splice site. e. Types of exons: the two types of exons are constitutive (always present in mRNA) and alternative (not always present in mRNA). III. mRNA half lifea. Definition: the time it takes for the starting amount of mRNA to decrease by halfb. AU-rich elements: bind in the 3’ non-coding region of the mRNA and contribute to determining mRNA half-life. IV. RNA interferencea. Mechanism: transcription of micro-RNA occurs in the nucleus. The miRNA is thenfolded into a hairpin loop and transported into the cytoplasm. Either pre-miRNAor pre-siRNA are cut into a short segment by a dicer and become mature mi or siRNA. This miRNA or siRNA binds to a protein complex (RISC complex). One of the miRNA or siRNA strands degrades and the other associates with the target mRNA through complementary base pairing. The mRNA then either degrades or is silenced.b. Non-coding RNA: an RNA molecule that does not code for a protein.c. miRNA hybridization: the reason that miRNA binds to a specific mRNA is because it hybridizes with the mRNA that is its complement. d. RNAs in RNA interference: these RNAs are encoded by the genome, encoded by viruses, or synthesized by
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