12.5 Gene Regulation

1. Gene Regulation In any organism, only a few genes are expressed at each time Operon: group of genes that operate together Scientists study E. coli gene expression of the lac operon

2. E. Coli lac Operon Allows bacteria to use lactose (sugar) as food Genes are turned off by repressors Genes are turned on by presence of lactose in the cell

3. Removal of the Repressor Promoter: RNA polymerase binds to begin transcription Repressor protein will bind to operator to prevent transcription if it is not needed –Once lactose comes into the cell, the repressor will change shape and come off of the operator –Once the repressor is released, transcription can happen

4. Eukaryotic Gene Regulation Generally, eukaryotes do not have operons Eukaryotic regulation is much more complicated than prokaryotic TATA box –Shows where transcription should begin on the gene Before the TATA box, the promoters are found

5. Enhancer Sequences Where are they found? –located before the point where transcription begins What are three things they can do? –Some will open tightly packed chromatin –Some will attract RNA polymerase –Some will block access to genes

6. Cell specialization requires gene specialization All cells have all genes for that organism Some genes in certain cells will never be used Example: –Liver cells will never express the exact same genes needed in nerve cells in the brain

7. Development and Differentiation Cell differentiation: when the embryo is developing, the cells are not just going to divide, they will turn into specialized cells –Each of these specialized cells will have specialized structure and function

Hox Genes Show where differentiation should occur (cells and tissues) Master control gene Mutations in these genes can cause major developmental problems –Example: Drosophila melanogaster: replace the fly’s antennae with it’s legs – so legs were growing on the fly’s head

Hox Genes Hox genes are extremely similar in living things –Can be removed from one animal and put into another and will still work Example: mouse eye was put into a fly and the fly grew an eye on it’s leg