Chapter 16 - Chapter 16 - - - - - Double helical model o...

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Chapter 16 - Double helical model o DNA substance of inheritance o Nucleic acids direct own replication from monomers o T.H. Morgan genes located along chromosomes - Griffith’s Experiment (1928) o Trying to find vaccine form pneumonia o Fredrick Griffith studied streptococcus pneumonia bacteria that caused pneumonia in mammals had 2 strains 1 pathogenic (disease causing) and 1 nonpathogenic (harmless) o when he killed the pathogenic bacteria with heat then mixed the cell remains with living bacteria of nonpathogenic strain, some of the living cells became pathogenic newly acquired trait of pathogenicity was inherited by ALL the descendants of the transformed bacteria o Griffith defined as – TRANSFORMATION- change in genotype and phenotype due to assimilation of external DNA by a cell. o **figure 16.2, pg 306 Griffith’s Exp. On Rats - Oswald Avery o Focused on 3 main candidates: DNA, RNA (the other nucleic acid), and protein. o In separate samples, he used specific treatments that inactivated each of the 3 types of molecules. tested each for its ability to transform love nonpathogenic bacteria. o Only when DNA was allowed to remain active did transformation occur. DNA = transforming agent - (1944) Avery, McCarty and MacLeod announced transforming agent was DNA o Represent Griffith? (+) enzymes to dest. Lip. 1. Lipids 2. Carbs 3. Protein 4. RNA o Transformation still occurred only DNA was left. - Hershey and Chase Exp. (1952) o Performed exp. Showing that DNA is the genetic material of a phage known as T2. o Bacteriophage- “bacteria- eaters”- viruses that infect bacteria. Can also just be called “phages”. A virus = little more than DNA enclosed by protective coat, often is a simple protein. To reproduce, a virus must infect a cell and take over the cell’s metabolic machinery.
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o T2 composed almost entirely of DNA and protein T2 phage could quickly turn E. coli cell into a T2 producing factory. T2 could reprogram host cell to produce viruses. o Hershey and Chase exp. fig. 16.4, p. 307 Which was the viral component- DNA or protein- responsible? Their exp. Showed that only 1 of 2 components of T2 enters the E. coli cell during infection To find out, they added sulfur to tag the protein since protein contains sulfur and they added phosphorus to the DNA to tag it. They tested 2 samples shortly after the onset of infection to see which type of molecule (protein or DNA) had entered the bacterial cells and therefore would be able to reprogram it. They found that the phage DNA entered the host cells but the phage protein did not. when these bacteria were returned to a culture medium, the infection ran its course, and the e. coli released phages that contained some of the radioactive phosphorus, showing that the DNA inside the cell played an ongoing role during the infection process. They concluded that the DNA injected by the phage must be the
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This note was uploaded on 11/13/2011 for the course BIOLOGY 1132 taught by Professor Shannon during the Spring '10 term at The University of Texas at San Antonio- San Antonio.

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Chapter 16 - Chapter 16 - - - - - Double helical model o...

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