Chapter 11 - Nucleic Acid Structure and DNA Replication

Chapter 11 - Nucleic Acid Structure and DNA Replication -...

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Click to edit Master subtitle style 4/30/11 NUCLEIC ACID STRUCTURE AND DNA REPLICATION CHAPTER 11
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4/30/11 To fulfill its role, the genetic material must meet several criteria 1. Information : It must contain the information necessary to make an entire organism 2. Replication : It must be copied In order to be passed from parent to offspring 3. Transmission : It must be passed from parent to offspring 4. Variation : It must be capable of changes IDENTIFICATION OF DNA AS THE GENETIC MATERIAL
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4/30/11 Griffith studied a bacterium ( Diplococcus pneumoniae ) now known as Streptococcus pneumoniae S. pneumoniae comes in two strains S Smooth Secrete a polysaccharide capsule Protects bacterium from the immune system of animals Produce smooth colonies on solid media R Rough Unable to secrete a capsule Frederick Griffith Experiments with Streptococcus pneumoniae
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4/30/11 In addition, the capsules of two smooth strains can differ significantly in their chemical composition n Rare mutations can convert a smooth strain into a rough strain, and vice versa - typeII S to a typeII R and vice versa
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4/30/11 Griffith concluded that something from the dead type IIIS was transforming type IIR into type IIIS He called this process transformation The substance that allowed this to happen was termed the transformation principle
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4/30/11 Avery, MacLeod and McCarty realized that Griffith’s observations could be used to identify the genetic material They carried out their experiments in the 1940s At that time, it was known that DNA, RNA, proteins and carbohydrates are major constituents of living cells They prepared cell extracts from type IIIS cells containing each of these macromolecules Only the extract that contained purified DNA was able to convert type IIR into type IIIS The Experiments of Avery, MacLeod and McCarty
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4/30/11 n Avery et al also conducted the following experiments To further verify that DNA, and not a contaminant (RNA or protein), is the genetic material
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4/30/11 Hershey and Chase 1952, studying T2 virus infecting Escherichia coli Bacteriophage or phage It is relatively simple since its composed of only two macromolecules DNA and protein
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4/30/11 The Hershey and Chase experiment can be summarized as such: Used radioisotopes to distinguish DNA from proteins 32P labels DNA specifically 35S labels protein specifically Radioactively-labeled phages were used to infect nonradioactive Escherichia coli cells After allowing sufficient time for infection to proceed, the residual phage particles were sheared off the cells => Phage ghosts and E. coli cells were separated Radioactivity was monitored using a scintillation counter Hypothesis Only the genetic material of the phage is injected into the bacterium § Isotope labeling will reveal if it is DNA or protein
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4/30/11 n These results suggest that DNA is injected into
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Chapter 11 - Nucleic Acid Structure and DNA Replication -...

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