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Lecture 18

Biology 1002B Lecture 18: Class 18 - Development and Death

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Western University
Biology 1002B
Denis Maxwell

Class 18 Development and Death Main mechanisms of epigenetic regulation Epigenetic = regulation that persists throughout generations or cell lines Gene expression is inherited from parent cells; not determined by each daughter cell 2 epigenetic mechanisms = feedback loops and chromatin packaging Feedback loops: product of a gene associates with its promoter; stimulates more of its own transcription o Important for differentiationdedifferentiation of tissue types Chromatin packaging: densely packed histoneDNA regions are called heterochromatin; most genes in these regions are silenced. Histones can be modified by acetylation, methylation, or phosphorylation Different types of mutations in protein coding genes Silent Mutation Could have a SNP that results in no change in the amino acid sequence You can have much more variation in DNA than what shows up in protein sequence; this is due to the redundancy in the genetic code Missense Mutation Could change DNA that results in change in a single amino acid Effect: improper folding of protein or could have no effect at all Nonsense Mutation Type of missense mutation which results in a premature stop codon Polypeptide is ended too early; can have dramatic consequence if stop codon is early Frameshift Mutation Often the most devastating mutation; caused by indels Results in reading frame being off; every single amino acid after mutation is wrong Likely effect of various types of mutations on gene expression Silent: No effect on polypeptide formation Missense: Hard to predict effect due to variety of possibilities Nonsense: Usually causes failure of suitable protein creation because of the protein being too short via premature stop codon Frameshift: Devastating! messing up of the amino acids afterwards of the deletedadded base pair Given the genetic code, identify mutations as missense, nonsense, or silent Missense: one codon is changed to another in the DNA, amino acid in protein is also changed. Impact can be hard to predict, may have little impact or could be devastating to protein function Nonsense: mutated base creates a stop codon mid protein, causes premature termination of the protein Silent: mutated base pair, change in mRNA but same amino acid appears in polypeptide chain. Change occurs in DNA sequence, but not in protein, mutation is invisible to selection Characteristics that make Drosophila an attractive model system Able to make two organisms from one genome: a larva and a fly
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