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Chapter 7-1.docx

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University of Lethbridge
BIOL 2000
Joseph Rasmussen

Chapter 7 March 18, 2013 DNA Structure and Replication What is the genetic material?  Main cellular components: o Polysaccharides, lipids, proteins, DNA, RNA?  Pre 1944 it was believed that protein was more likely than DNA to be the genetic material: o 20 standard amino acids in proteins, only 4 different nucleotides in DNA  Correct o DNA sequence thought to be repetitive (AGCTACT…..)  Now known to be incorrect  E.Coli 25% of each nucleotide- this is what brought on this belief Frederick Griffith 1928  Transforming Steptococcis R cells into S cells  Death Requires productive infection o S strain  R strain has nothing going on  S strain heat killed o No productive infection  R strain + heat killed S strain o Productive infection o All the bacteria within the mouse was transformed  Conclusion o Component from dead S cells is taken up and transforms R cells with virulence properties o The transformed R cells divide and propagate as S cells  Heritable material was acquired  Passed Avery, Macleod and McCarty 1944  Which specific component of heat-killed S cells is required for transformation  Inactivated polysaccharides o Mouse dies- has no effect  Lipids destroyed o Mouse dies- no affect  RNA destroyed o Mouse dies- no affect  Protein destroyed o Mouse dies- no affect  DNA destroyed o Mouse lives- has affect o Evidence that DNA is genetic material Hershey and Chase- 1952  Differential labeling of phage components 35 o Proteins S- Labeled OR DNA P-Labeled  Shows that phage does not go into cell- but that something is being injected into the cells o Phage DNA or phage protein components?  Allow phage time to inject into cells o If proteins are genetic material- e.coli cell will have radioactive proteins o If DNA is genetic material- e.coli cell will have radioactive DNA  Conclusion 32 o Majority of radioactivity injected by phage into E.coli was P-labeled DNA o Phage DNA drive the production of new phage particles  Genetic information storage What are the chemical and physical properties of DNA?  Stability o Must maintain structure during the lifetime of an organism 
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