DNA: The Genetic Material Chapter 14

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

Griffith: Transformation

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

Hershey and Chase

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)

Phosphodiester Bonds Make backbone of DNA Formed by Dehydration Synthesis

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

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

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

Overview of Replication Initiation Elongation Termination

Prokaryotic Replication

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

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

Videos http://highered.mcgraw-hill.com/olc/dl/120076/micro04.swf http://highered.mcgraw-hill.com/olc/dl/120076/bio23.swf

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

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

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