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BIOL 239
Christine Dupont

Set 10 thinking back to chromosomal theory of inheritance there were observations that indirectly place the hereditary materials belonging to the chromosomes by microscopy techniques and tracking chromosomeswhat are the chromosomes made of And how do you link the genes to this substance2 Characterization of DNA1869identified nuclein as a weakly acidic phosphorousrich material from the nuclei of human white blood cellsIts major component later turned out to be DNA deoxyribonucleic acid1923Use of Schiff reagent which stains DNA red shows that it is almost exclusively within the chromosomesthey thought protein was the hereditary material3 DNAwhy can they stain with schiffs reagentits weakly acidic it gives up hydrogens in solution and its got a phosphate backbone on it Phosphorous rich which is easily recognizedbut that didnt prove chromosomes were made up of DNADNA is the hereditary material or is it protein4 Characterization of DNA The discovery of DNA was a chromosomal constituent did not establish that it had anything to do with genes Many scientists at the time pointed to proteins as the likely genetic material5 Use of bacteria to implicate DNA as the substance of genesBacteria carry their genetic material as a single circular chromosome without it being enclosed by a nuclear membrane prokaryotes1923Frederick Griffith we need to know Griffith performed studies with Streptococcus pneumonia he worked with prokaryotes because theyre easy to work with grow quickly and easy to controlstrep causes pneumonia It used to be a real problem It causes meningitis in children Now we are vaccinated for it Despite that many people still carry this organism asymptomatically in their upper respiratory tract strictly in humansusually not a problem only sore throat or ear infection not meningitishe took strains from humans and could get them to move in two forms smooth and roughTwo forms smooth S which is wildtype Rough RS are virulent R are notwhen you first isolate them from a throat culture and grow them on agar they have a muccoid shiny surface and when theyre in that phenotypic form they can cause infection and diseaseif you take smooth colonies and replate them passaging them eventually they adapt to the lab conditions of the plate mediaone adaptation is that the cells with the random mutations in them that hit the genes that produce that slimy phenotype outcompete the ones that are producing the smooth phenotypeyou start with smooth you get roughonly smooth can cause disease because theyre virulentthey have thick carbohydrate capsule slime layer around them so the immune system cant get around themphagocytes cant grab them properly if they lose the capsule no disease
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