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2012.03.05 - Bio 1202 Lecture Review Notes.docx

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Biology 1202B
Gardiner/ Murphy

Biology Lecture Review Notes Lecture 5 Gene Expression  Human egg when released from the ovary is almost completely inactive metabolically o There is no gene expression in the human egg (23 chromosomes in the egg)  Within seconds of the egg & the sperm meeting there is rapid cell division  Divisions produce cells of the body with specialized cells that differentiate with specialized functions o As the cells are dividing, the cytoplasm does not have to be divided perfect (therefore, protein components can be different between cells) o These protein differences cause the specialized functions  All 46 chromosomes in each cell are the same o The differences in cells result from which genes are transcribed and translated  It is not enough just to have a gene present in DNA o 20-30 thousand genes in the human genome o Gene must be expressed (or not transcribed) o In the correct tissue (spatial) o At the correct time (temporal)  Not all cells express all genes  Children typically do not survive if they have lethal development (genes are not well adjusted to the environment and are not tuned correctly)  Regulation of gene expression in eukaryotes is more complicated because nuclear DNA is bound to histones o Need chromatin remodeling to loosen histone DNA interaction (acetylases add acetyl groups to histones) or remove nucleosomes from the promoter region of the gene  Chromatin remodeling o Chromatin = DNA + RNA + proteins o Promoter DNA not accessible to proteins that need to bind to DNA to initiate transcription - gene is inactive o The nucleosomes are removed to expose the promoter o Promoter DNA is accessible - gene may be active  Still need the correct protein, spatial, temporal and transcription factors o Transcription factor can bind to the promoter to turn the gene on  Steps in gene expression – eukaryotes o Transcription regulation – which genes are turned on or off (transcribed) and in which tissue o Posttranscriptional regulation – types & availability of mRNAs to ribosomes  Not all mRNA goes through translation o Translational regulation - rate at which proteins are made o Posttranslational regulation - availability of finished protein  Not all parts of DNA encode for mRNA o Introns o Promoters and enhancers o Intergenic sequence (between genes) o Repeats (telomeres and centromeres)  Organization of a eukaryotic gene involving gene expression o Enhancer (regulatory sequences) - determine whether maximum rate of transcription is reached o Promoter proximal regions – increase rate of transcription o Transcriptional unit = 5’UTR, exons, introns, 3’UTR  Segment that is transcribed into the pre-mRNA o Promoter (often contains TATA box) - TF (nonhistone proteins) recognize & bind to the TATA and then recruit RNA polymerase II  Formation of transcription complex at the promoter st o 1 general TF recognizes & binds to TATA o Additional gener
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