31 - MCB 142 Professor Georjana Barnes 11/7/07 Lecture 31...

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MCB 142 Professor Georjana Barnes 11/7/07 Lecture 31 ASUC Lecture Notes Online (formerly Black Lightning) is the only authorized note-taking service at UC Berkeley. Please do not share, copy or illegally distribute these notes. Our non-profit, student-run program depends on your individual subscription for its continued existence. These notes are copyrighted by the University of California and are for your personal use only. Sharing or copying these notes is illegal and could end note taking for this course ANNOUNCEMENTS For those of you who weren’t here on Monday, I’m Georjana Barnes, the last in the series of professors you will face in this course. The bottom line of what we talked about last time was that diploid cells can undergo mitosis and meiosis, whereas haploid cells can only undergo mitosis and not meiosis. I want to remind everyone again that the course website has all the information on the course, such as my office hours. In addition, I will be using the bSpace website more than Professors Slatkin and Rokhsar did. What I plan to do is post the slides in pdf form on bSpace after lectures. What I’m showing in these slides will mostly be images from your book, so hopefully if you’ve read the chapter already, the figures will spark something in your memory. If you haven’t read it before lecture, then when you do, you’ll know what’s important because I will have talked about it in lecture. LECTURE GENE REGULATION IN PROKARYOTES What we’re going to talk about today should be more review for most of you who’ve taken Bio 1A or the equivalent. That’s the good news. But we’re going to go beyond the level of that. What we’re going to talk about today is gene regulation in prokaryotes. Hopefully you know the differences between prokaryotes and eukaryotes. To summarize briefly, prokaryotes are big bags of cytoplasm without internal organelles and no membrane- bound nucleus. A membrane-bound nucleus defines eukaryotes. I’m going to be showing you figures from the text. This is figure 17.2. This should be familiar to you, because you’ve read chapter 8 and you know all about transcription. This figure just summarizes what you already know. In prokaryotes, what you have happening is that you have an RNA polymerase core enzyme (tetramer) that associates with a sigma subunit; together, this complex binds to the promoter regions of DNA. It is the sigma subunit that does the DNA binding. Without the sigma subunit, the core polymerase won’t bind. The rest of this figure shows the rest of the process. So we have initiation, which is binding of sigma subunits with the core polymerase on the DNA. Then you have elongation, where the core RNA polymerase begins to unwind DNA and start the process of forming mRNA polymer. Then this interaction of the mRNA and the subunits of the core polymerase causes dissociation of the polymerase and sigma subunits. Now the whole compound is not stuck at the promoter. The sigma subunit releases polymerase and DNA polymerase
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31 - MCB 142 Professor Georjana Barnes 11/7/07 Lecture 31...

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