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Biology 1202B
Shauna Burke

Lecture 5: Control of Gene Expression ( Chapter 15) - MURPHY LECTURE Human Development - Human egg when released from the ovary is almost completely inactive metabolically - Within seconds of the egg & the sperm meeting, rapid cell division - Divisions produce cells of the body with specialized cells that differentiate with specialized functions * 23 chromosomes in an egg, through those divisions, daughter cells have identical DNA but different proteins resulting in different specialization - Every nucleated cell of the body contains the same DNA template and genes * nucleated = cell that has a nucleus, i.e there are nucleus and DNA within these cells structurally and functionally there are differences between cells and what they express Then how do cells of a developing embryo, with the same set of DNA/genes, create vastly different, spe- cialized cells? nucleated = cell that has a nucleus, i.e there are nucleus and DNA within these cells structurally and functionally there are differences between cells and what they express Structural & functional differences in cell types result from the presence or absence of the products,i.e. which genes are transcribed? which genes are translated? rather than the ac- tual presence of genes themselves on DNA - It is not enough just to have a gene present in DNA - Gene must be expressed (or not transcribed) in the correct tissue at the correct time - Very complex system * 20-30000 genes they have the ability to be turned on and turned off, must be expressed, the correct time and tissue ( all have the potential) Gene is like music played by an orchestra Gene is present in DNA but is it “On” or “Off” i.e. transcribed or not - on = Gene is being expressed - off = Gene is not being expressed - in different tissues this may change, at different times this may change Gene is individual fine tuned - loud (forte) vs quiet (piano) - dynamics (crescendos, decrescendos) - staccato (short 1/2 life) vs legato (long 1/2 life) Gene’s tuning is dynamic & aware of its surrounding you adjust your “volume” relative to “other volume” around you, If done properly you get music If not, you get noise Regulation of Gene Expression in Prokaryotes Simple, single celled organisms with generation times in minutes Rapid & reversible alterations so they can adapt quickly to changes in their environ- ment - Genes are organized into a functional unit called an operon i.e. coordinated synthesis of pro- teins with re- lated functions i.e Lac operon is an example of transcriptional regulation demonstrating how genes are turned on & off * prokarytotes, genes organized into functional unit, operon co ordinate synthesis of similar functional proteins Regulation of Gene Expression in Eukaryotes Multicellular cells. More complicated since nuclear DNA is bound to histones thus need chromatin remodeling to loosen histone DNA interaction (acetylases add acetyl groups to histones) or remove nucleosomes from the promoter region of the gene Promoter DNA not accessible to proteins that need to bind to DNA to initiate transcription Gene is inactive 1. either displace a nucleosome 2. acetylase to loosen association of histone a DNA, even if there is a right conformation of DNA transcription factors are tissue specific Promoter DNA is accessible Gene may be active by removing nucleosomes Regulation of Gene Expression in Eukaryotes Multicellular cells More complicated since nuclear DNA is bound to histones (thus need chromatin remodeling to remove/loosen nucleo- somes from the promoter) produce a large number of cells produce a large number of different types of cells transcription regulation: determines which genes are translated, Which genes Transcribed, Most VIP post transcription regulation:determines types and availability of mRNAs to ribo- somes, Types & availability of mRNAs to ribosomes translation regulation determines rate at which protein are made, Rate at which proteins are made post translation regulation determine availability of finished protein, Availability of finished protein Central Dogma DNA → mRNA → Protein But do all parts of DNA encode for mRNA ? No 46 chromosomes, 6 billion nucleotides they all don’t code for mRNA i.e introns are taken out DNA that does not encode mRNA: Introns, Promoters, enhancers, In-
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