3_8 - lecture 3/8/07 PROKARYOTIC GENE REGULATION Most of...

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lecture 3/8/07 PROKARYOTIC GENE REGULATION Most of our DNA is genes…only 3-5% genes are transcribed in the cell. Why are there so many that aren’t being transcribed? There will be a lot of genes in the cells that the cell will never express. So many genes are turned off (regulated and usually untranscribed) because of tissue differentiation- genes that are specific to different tissues. Also, the zygote contained all the genes that would be necessary at every developmental stage, cells have all the genes that were used at a certain stage in life, and aren’t being used right now. Also, there are some genes that only need to be transcribed in certain positions or environmental states. Cells need to have this kind of flexibility to have all these genes, and also have a way of controlling which genes are being transcribed, and which ones aren’t. 1.) Transcription- gene transcribed, or gene not transcribed. 2.) RNA processing (post-transcription)- if the processing event is delayed, then the gene product isn’t actually made. RNA stability - snip the tails off the mRNA, no more genes of that type. 3.) Translation- does it happen or not? Could be a protein that binds at the 5’ cap and blocks recognition from the 40S subunit. A little piece of RNA that is complementary to the 5’ untranslated region of the mRNA could also block translation (double stranded RNA is characteristic of certain viruses, makes cells “nervous,” so cells are geared towards turning double- stranded RNA to destruction - same idea for gene regulation) 4.) Post-translation- phosphorylation of proteins as a common post- translational modification (adding phosphates can make the protein functional), modifying the number of phosphates can switch the functionality on and off. Which one is most common? Transcription (during initiation). Period where there is less energy, less resources used. Prokaryotic system: lac operon Lactose should have something to break it down (proteins), so you need the genes to encode those proteins. Lactose is broken down by an enzyme by B-galactosidase, which splits it into into glucose and galactose. If lactose and b-galactosidase are available, there will be a trace amount of allolactose around.
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Permease- channel protein (membrane protein). Need permease to let the lactose into the cell, and need B-galactose which catabolizes lactose into other easily-used products. Transacetylase
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This note was uploaded on 04/15/2008 for the course BIO 325 taught by Professor Saxena during the Spring '08 term at University of Texas at Austin.

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3_8 - lecture 3/8/07 PROKARYOTIC GENE REGULATION Most of...

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