dna: the genetic material chapter 14. what is the genetic material? protein vs dna griffith, avery,...
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DNA: The Genetic Material
Chapter 14
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What is the genetic material?
• Protein vs DNA
• Griffith, Avery, Macleod and McCarty, Hershey and Chase
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Griffith: Transformation
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Avery, MacLeod, an McCarty• Repeated Griffiths except removed almost all Protein
from the viri• 5 findings
– 1. The elemental composition agreed closely with that of DNA
– 2. When spun at high speeds in ultracentrifuge it migrated to the same level as DNA
– 3. Extracting lipids and proteins did not reduce transforming activity
– 4. Protein- digesting enzymes did not affect transforming activity, nor did RNA digesting enzymes
– 5. DNA-Digesting enzymes destroyed all transforming activity
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Hershey and Chase
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DNA Structure• Miescher
• Components known but structure and mystery– 1. A FIVE-carbon sugar– 2. A phosphate group– 3. A nitrogen containing base ( purine vs
Pyrimidine)
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Phosphodiester Bonds• Make backbone of DNA
• Formed by Dehydration Synthesis
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Chargoff, Franklin, and Wilkins
• Chargoff’s rules– A=T, and G=C– There are always an equal number of
Purines and Pyrimidines
• Franklin and Wilkins worked with x-ray diffraction
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Watson and Crick
• Took everyone else’s information and built a model
• 1. Phosphodiester backbone
• 2. Complementarity of bases
• 3. Antiparallel configuration
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Meselson and Stahl
• Looking at DNA replication
• 3 possibilities– Conservative– Semiconservative– Dispersive
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Overview of Replication
• Initiation
• Elongation
• Termination
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Prokaryotic Replication
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DNA replication Enzymes• Polymerase 1-acts on lagging strand to
remove primers• Polymerase 2- involved in DNA repair• Polymerase 3- main replication polymerase• Helicase- Unwinds DNA• Gyrase- lowers torsional strain• Primase- synthesizes RNA primers• Ligase- joins the ends of DNA segments• SSB- stabilizes single stranded regions
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Imporant Facts about DNA replication
• Occurs in the 5’ to 3’ direction– Leading strand and Lagging strand
(Okazaki fragments)
• Occurs in a repication fork
• Beta subunit holds pol III on
• Replisome contains all necessary enzymes for replication
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Videos
• http://highered.mcgraw-hill.com/olc/dl/120076/micro04.swf
• http://highered.mcgraw-hill.com/olc/dl/120076/bio23.swf
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Eukaryotic Replication
• Complicated by the larger amount of DNA and Linear structure of the chromasomes
• Multiple Origins• Same enzymes but they are more
complex• Telomerase signals the end of
replication
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Why is Telomerase important?
• When it doesn’t work the ends or Telomeres of DNA gradually shorten– This leads to aging – Linked to cancer
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DNA Repair
• Mutagens constantly cause damage
• DNA repair can restore damaged DNA
• Specific– Photorepair using thymine dimer
• Non specific– Excision Repair