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DNA: The Genetic Material

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Presentation on theme: "DNA: The Genetic Material"— Presentation transcript:

1 DNA: The Genetic Material
Chapter 14

2 What is the genetic material?
Protein vs DNA Griffith, Avery, Macleod and McCarty, Hershey and Chase

3 Griffith: Transformation

4 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

5 Hershey and Chase

6 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)

7 Phosphodiester Bonds Make backbone of DNA
Formed by Dehydration Synthesis

8 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

9 Watson and Crick Took everyone else’s information and built a model
1. Phosphodiester backbone 2. Complementarity of bases 3. Antiparallel configuration


11 Meselson and Stahl Looking at DNA replication 3 possibilities
Conservative Semiconservative Dispersive


13 Overview of Replication
Initiation Elongation Termination

14 Prokaryotic Replication

15 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

16 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


18 Videos

19 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

20 Why is Telomerase important?
When it doesn’t work the ends or Telomeres of DNA gradually shorten This leads to aging Linked to cancer

21 DNA Repair Mutagens constantly cause damage
DNA repair can restore damaged DNA Specific Photorepair using thymine dimer Non specific Excision Repair

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