36 - MCB 142 Professor Georjana Barnes 11/19/07 Lecture 36...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
11/19/07 Lecture 36 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 Office hours next week will be Monday and Wednesday. There are sections this week. Those of you who have discussion sections Wednesday afternoon, there will be section. If you have sections you can’t make, go to some other GSI’s section. The deadline for regrades is next week, November 26. At any point, you can give it to your GSI. But the grader will be here Monday to pick them up. Question: Will there be class here on Wed? Answer: Yes. REVIEW So what we have been talking about for a long time is eukaryotic gene regulation. Up until last time, we’ve been talking about regulating transcription. We talked about activators, repressors, and chromatin structure and we’re going to continue with genomic imprinting. This slide should be familiar. You have cis- acting elements and transcription factors that activate or repress. Last time, we saw that chromatin structure influences gene expression and that’s because we’ve been thinking about transcription factors as binding to naked DNA but that’s not the case. In cells, DNA is packed into a structure known as chromatin where you have histone proteins that wrap DNA around. Packing DNA into chromatin goes a long way towards reducing basal transcription. In prokaryotes, transcriptional regulation has a lot to do with repressing transcription because you don’t have chromatin structure to lower basal transcription. So if you recall, in prokaryotes, we talked about factors that turned down transcription and in the absence of those repressors, you had expression of genes. But in eukaryotes, it’s a different story because the chromatin structure serves to turn down basal transcription. Then we saw that what eukaryotic cells do to turn promoters on is to have remodeling proteins (in yeast, SWI-SNF) that push nucleosomes out of the way and make the promoter accessible. We can tell the difference between active and inactive genes because active genes have these DNA-hypersensitive sites that inactive genes don’t have because they’re physically shielded from cleavage by DNase. SILENCING BY HYPERMETHYLATION Normal chromatin looks like this. The basal transcription is way down and remodeling factors have to shove nucleosomes out of the way to activate promoter. So transcription is way down but it can be turned down even further, or shut down completely, by hyper-methylation in eukaryotic cells. So this is an example of where DNA’s been hypermethylated. Hypermethylation is occurring on cytosines in CpG dinucleotides. Hypermethylation
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 5

36 - MCB 142 Professor Georjana Barnes 11/19/07 Lecture 36...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online