DNA: The Genetic Material Chapter 14. What is the genetic material? Protein vs DNA Griffith, Avery,...

DNA: The Genetic Material

Chapter 14

What is the genetic material?

• Protein vs DNA

• Griffith, Avery, Macleod and McCarty, Hershey and Chase

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

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

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

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

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