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Unformatted text preview: MCB 102 James Berger 3/17/08 Lecture 24 Sharing or distribution of lecture notes, or sharing of your subscription, is be prosecuted. Our non-profit, student-run program depends on your individual subscription for its continued existence. ILLEGAL and will 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 LECTURE Lets go ahead and get started then. To recap from last time we spent most of the last lecture talking about genomic analyses. We talked about the concept of libraries: genomic libraries, cDNA libraries, etc. We talked about sequencing, and how sequencing is changing a lot of fields in biology. We talked about microarrays as well. One of the things that all of these analysis tools have in common is that many of them rely on polymerases . As you recall, we started talking about polymerases before we began to segue into cloning and methodologies of that sort. Within polymerases we talked about several aspects of their structure. For instance, polymerases are constructed much like a right hand with fingers, a palm, and a thumb. Those elements work in concert to make sure that they carry out nucleotide addition in an appropriately faithful manner. We talked about how that fidelity or accuracy is imparted by elements of the polymerase and the fact that polymerases are not distinguishing the Watson- Crick base pairing within base pairs, but rather the shape complementarily between base pairs. Thats an important point. Despite the fact that polymerases are as accurate as they are, about 10 4- 10 6 , they have additionally proofreading elements that are exonucleases which backtrack when the polymerase makes a mistake, excise the erroneous nucleotides from the base pair, and reinsert new ones. We also talked about the fact that polymerases are constrained by the fact that we use 5 nucleoside triphosphates, so they must synthesize in a 5 to 3 direction. As you probably already gathered, cells actually have a large number of different kinds of polymerase. There are multiple types of polymerases inside the cell. This chart shows just a few examples of those. In E. coli, there are actually five polymerases. Three of them are listed here: DNA polymerase I, II, and III . These vary in terms of their molecular weight, also in terms of their accuracy or fidelity, whether they have certain exonucleases on them, etc. You might wonder why the cell needs so many polymerases. It is because copying DNA is not just as simple as laying down a new strand. For the cell, it is very important to make sure that the DNA is synthesized at an appropriate time and appropriate place. The synthesis machinery is coordinated with other types of events that are also going on in the cell. E. coli has approximately five or so polymerases. Two of the polymerases which are not on this list are used exclusively for DNA repair....
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This note was uploaded on 05/07/2008 for the course MCB 130 taught by Professor Schekman during the Spring '08 term at University of California, Berkeley.
- Spring '08