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Chapter 13 Blog: Gene Regulation  (Emad)

Page history last edited by Emad Madha 13 years, 4 months ago

In the first section of this page, you will write a daily summary of that day's class.  For example in  your chapter 2 blog, your first entry should be titled 9/3/10.  You should then write a one or two paragraph summary of that day's lecture, outlining the major points.  In the second section, you are required to add two items (link to a website, video, animation, student-created slide show, student-created PowerPoint presentation) and one journal article pertaining to a topic in this chapter.  A one-paragraph summary must accompany each item describing the main idea and how it applies to the lecture topic.  Please see the PBWorks help guide for assistance embedding video and other items directly in the page.  I will also produce a how-to video on using tables to wrap text around items and other useful tips.  Please see the syllabus for organization and grading details.


A.  Daily Blog


This chapter is about the regulation of gene expression. By that, it means how the cell controls how much a gene is expressed, resulting in various amounts of gene product (proteins). The processes for the regulation of gene expression vary in prokaryotes and eukaryotes. We began by discussing the prokaryotic process. In prokaryotes, genes are grouped together by common function, and all the genes of the similar function are turned on and off by a single promoter. This complex is known as an operon. Specifically, we looked at the example of the lac operon, which regulates the metabolism and transport of lactose. The lac operon consists of the lac P (promoter), the lac O (operator), CAP site, lac I (codes for the repressor) and the lac Z, lac Y, and lac A structural genes that are coded to regulate the metabolism and transport of the lactose. The lac P is the promoter region, where the RNA polymerase begins transcription. The lac O and the CAP site are regulatory regions which enhance the rate of transcription. The lac Z, lac Y, and lac A are the genes that are coded during transcription. The lac I gene has only one function, which is coding for the repressor protein. The gene is therefore considered a regulatory gene. The repressor protein will bind to the operator site, inhibiting transcription of the lac Z, Y, and A genes.

Eukaryotic regulation is more complicated. Unlike prokaryotic regulation, which can be thought of as a light switch, the eukaryotic regulation isn't as straightforward. In eukaryotes, regulation is more like a dimmer light, where variable amounts of gene products are produced at a time, depending on the need for the gene product. In eukaryotic cells, the DNA is packaged extremely tightly, and is not as accessible as prokaryotic DNA. Thus, for transcription, the chromatin must be unwound. Depending on how tightly a region of the chromatin is wound, the gene expression may be at a higher rate or at a lower rate. In eukaryotes, there are activator and repressor proteins that affect the ability of RNA polymerase to transcribe, as there are in prokaryotes. But the genes in eukaryotes are almost always organized individually. In eukaryotes, there is what is known as combinatorial control. Multiple activators and repressors affect RNA polymerase activity. The function of the activators and repressors may be affected by small effector molecules, protein-protein interactions, and covalent modifications. The tightening and loosening of the chromatin affects the amount of gene product. To start transcription, 3 proteins are necessary. The RNA polymerase, the GTFs (generel transcription factors), and mediators (which bridge the interactions between the RNA polymerase and regulatory proteins). These all form the complex to begin transcription. They form at the core promoter, at the TATA box, a precise starting point that is 25 bp upstream from the transcriptional start site. Mediators play an important role in the rate of transcription. They bind to activators and repressors, which are far upstream at regions known as enhancers or silencers (activators to enhancers, repressors on silencers), which increase or decrease transcription, respectively.

Some genes are not regulated, and are known as constituitive genes, which perform "housekeeping" activities in the cell. Most genes are regulated though, toconserve energy and ensure that genes are expressed at the right time in the right environment.


B.  Useful Materials


This video outlines gene regulation in prokaryotes. It uses the lac operon as an example.


This video outlines eukaryotic gene regulation. The woman in the video appears to use a pad similar to one that Dr. Weber uses in lecture. 




MicroRNA Expression in Rat Brains

This paper discusses an experiment regarding MicroRNA. Laboratory rats were subjected to shock therapy (ouch) and were tested to see if they had "Learned Helplessness". The levels of miRNA were measured in the frontal cortex of the rats. Non-learned helpless rats had higher rates of miRNA activity than those with LH. The scientists concluded that miRNA participates in alterations of gene expression networks that regulate non-learned helpless rats, and presumably don't participate in those networks of learned helpless rats in response to repeated shocks. (Sounds like a lot trouble for the rats. May be the shocks that make them stupid, not the lack of miRNA activity :P)





Comments (1)

Derek Weber said

at 12:24 am on Feb 16, 2011

Use the learning objectives when writing your summary. What happened to processing?

Be a bit more descriptive in your summaries of your items.

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