Lecture09S10

Lecture09S10 - BIS101/Engebrecht Lecture09 Announcements I...

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BIS101/Engebrecht 4/16/10 Lecture09 Announcements: I have posted the key to the practice midterm and Homeowork02. Please see powerpoint for office hours/review session times. Midterm next Thursday – will let you know room assignments by Tuesday. We began our discussion of bacterial genetics (please see outline ). We discussed the properties of bacteria that make them important tools for studying basic cellular processes like DNA replication, transcription, and translation. Bacteria are prokaryotes, that is they lack membrane- bound organelles, and have a single (usually), circular chromosome. They have a very fast generation time (20 min) and one can literally look at billions of individuals. Unlike the other organisms we have been discussing, bacteria do not undergo meiosis but they do recombine. Understanding bacteria is important, as E. coli, is the workhouse for modern day molecular biology and thus it is likely that you will use this bacterium in almost any type of research program. Bacteria are also important because they are the causative agents for a number of diseases and have “outsmarted” humans in escaping death by antibiotics. Therefore, there is still a lot we can learn by studying them. As a geneticist, you want to be able to isolate mutants to dissect a pathway. What type of mutants can you isolate in bacteria? Unlike plants, drosophila and human, it is not easy to isolate morphological markers but it is easy to identify nutritional markers. Wild-type bacteria are said to be prototrophic , that is they can grow on medium containing, inorganic salts, a carbon source and water. From these compounds they are able to synthesis everything they need to grow. If you identify a mutant that fails to synthesis a particular compound, say the amino acid leucine, they are now said to be auxotrophic. That is, they require leucine to grow. Please look at the outline for a little blurb on Bacterial nomenclature. I would also like you to understand the difference between a screen and a selection. Screen = a mutagenesis procedure in which all mutagenized progeny are recovered and individually evaluated for the mutant phenotype . Our example was looking at leucine auxotrophy. In this case, you can not select for lack of growth on medium lacking leucine because you will lose the class of mutant you are interested in. Selection = experimental procedure in which only a specific type of mutant can survive
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Lecture09S10 - BIS101/Engebrecht Lecture09 Announcements I...

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