Test 3 - Control of Gene Expression o o o Why? Where? -...

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1. Control of Gene Expression o Why? o Where? - occurs at transcription, but other places as well o When? - whenever a cell is going to get a new protein 2. Transcripts are Edited o In Eukaryote Cells, m-RNA has a cap and tail added o There is a front end and a back end that m-RNA has. These can be protective and can help direct where the transcript goes. Additionally, the length of DNA has sequences of bases that do not code for the protein. These parts are spliced out…so that the parts for the polypeptide can be put together, and the others are 'wastes' Some parts are removed (introns) and others remain to be expressed (exons) o Splicing Alternative splicing may make more products One length of DNA might make for more than one product 3. Control of Gene Expression: Prokaryotes o Prokaryotes: are simple - don't have introns o Operons (set of genes that work together to eventually result in a product) Has an 'on' and 'off' switch for the gene The whole groups that operate together o Lac Operon A sequence of genes that produces an enzyme to break down milk sugar (unrelated to lactose intolerant). A prokaryote gene (set of genes). In these bacteria, they need to make enzymes to break down milk sugar when present. So the enzymes are called lactose utilizing genes Protein has 'projections'. This protein when it is made, binds with DNA that is farther upstream than the lactose utilizing genes. The gene has made a protein that has 'turned off the gene'. The lactose utilizing genes are turned off. When there is milk sugar present, it combines with the 'switch' or protein that was blocking the gene from being expressed. This changes the shape of the protein, preventing it from being bound to the DNA. The switch is on. After the enzymes are made and break down the milk, the protein is free to bind to the DNA, meaning that the gene becomes turned off again. --Suppose a mutation occurred in a 'control' gene of the operon, so that the protein couldn't be made at all, what would happen? The enzyme would be made all the time. Mutations are important in the code for making the product, but they can also be extremely detrimental to when on the 'control' gene 4. Control of Gene Expression o Genes may be turned off or on by signals from other genes: important in development o Embryo A multi-celled embryo stage - cells are already different.
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A protein from one cell leaves the cell and binding with a signal receptor on an adjacent cell. This cell is telling the other cell what to do - turning genes on and off. Nearby cells induce other cells to take a certain path. Location of the cell determines what the cell will be 5. Embryo Development o Unfertilized eggs: uneven distribution of enzymes, RNAs, yolk, etc. If you imagine an egg in an ovary, that egg or cell already has an
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This note was uploaded on 04/27/2008 for the course BIOL 101 taught by Professor Hogan during the Spring '08 term at UNC.

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Test 3 - Control of Gene Expression o o o Why? Where? -...

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