Microbiology Day 18 - Microbiology Day 18 March 21st Slide...

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Microbiology Day 18 – March 21 st Slide 17 Historically, its has been used for mapping gene order, study mutants, etc. Example include Cotransduction, where you look for two genes are transduced together and that’s made for mapping. The neared the genes are on genome of the bacteria, the more they will be transduced together. Two-factor crosses, to see if genes are linked Three-factor crosses can be used to map order of genes. The difference between cotransduction and two factor cross. Just because two genes are transduced together, doesn’t tell you how close the genes are. So two factor one does determine how close they are so they’re about the same thing ???(what’s the difference). Slide 22 You transduce recipient cells and in this case, the donor cells are positive for the met B and argH, meaning they have active proteins. You then transduce them that require both of them (selective media). You look for ability for ability to grow on media without one of them and then you test to see how many are Arg+ and metB+. The higher the frequency, the closer they are. With bacteria, when we see genes linked, we talked about genes that are close together. On the right side, they’re not linked so you don’t see them often but if they are close together, then you do see them often. Slide 23 We can use this to determine the order of the gene. So I wouldn’t give data for this, but you want to see what order the genes are in and why that happens. So if we look at class one, out first selection criteria is A and we see along with A, how often do you see A, B and AB. This order suggest that A+, B- and C+ is linked Slide 24 Lambda is used for checking specialized transduction, whereas P1 is used more for general transduction. Lamda and P1 behave a bit differently and most of the stuff about bacteriophage is with lambda, but there are some differences with P1. A few things to note is the cos site on lambda is at the end of the genome. So the cos sites allow for circularization of viral genome when it enters into cytoplasm so you see this in bacterial cytoplasm. Cos stands for cohesive, so it’s like RE that have sticky ends. When they come into bacterial cytoplasm, they come together, so that ligation is done by host or virus enzymes. In bacterial cytoplasm, it ciruclarizes and is needed for lysogeny. The P1 system is a lot more different and is more complex. The P1 has variable size in a population (lysate). So after its gone in a cell and lyse them, from lysate they’ll have a random wide range of sizes of capsid. It has about 120 genes which is big and normally, they would have only a few. P1 also has 28 proteins in the capsid and tail, so it makes a lot of proteins that aren’t involved in the protein coat (which is unusual to make so many proteins or RNA) and doesn’t rely too much on the host. An interesting thing is dar genes in the virus make a protein that protects the viral DNA
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from RE attack. Normally, that’s how a bacteria protects itself and it’s suppose to chop up any invading DNA (since it doesn’t have antibodies).
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