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DNA: Prince of the Chemicals

Explore the transformation of bacteria from harmless to virulent strains through landmark experiments such as Griffith, Avery, MacLeod, and Hershey-Chase. Learn about the genetic material, nucleotides, base pairing, and the Watson-Crick model of DNA.

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DNA: Prince of the Chemicals

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  1. DNA:Prince of the Chemicals Timothy G. Standish, Ph. D.

  2. Capsules Transformation Of BacteriaTwo Strains Of Streptococcus Rough Strain (Harmless) Smooth Strain (Virulent)

  3. + Control - Control - Control Experimental Transformation Of BacteriaThe Griffith Experiment OUCH!

  4. Enzyme Transformation? Avery, MacLeod and McCarty • 1944 Avery, MacLeod and McCarty decided to repeat Griffith’s 1928 experiment and try to discover the “transforming factor” • They did this by using extracts from the heat- killed cells and digesting specific classes of molecules with enzymes Lippase Yes Protease Yes Saccharase Yes Nuclease No

  5. H H O O OH H2N C C H2N C C NH2 Methionine Cysteine OH OH P O HO CH2 CH2 O Some amino acids contain sulfur, thus proteins contain sulfur, but not phosphorous. SH CH2 Nucleotides contain phosphorous, thus DNA contains phosphorous, but not sulfur. S CH3 H OH The Hershey-Chase Experiment • The Hershey-Chase experiment showed definitively that DNA is the genetic material • Hershey and Chase took advantage of the fact that T2 phage is made of only two things: Protein and DNA

  6. T2 grown in S35 containing media incorporate S35 into their proteins Bacteria grown in normal non-radioactive media T2 attach to bacteria and inject genetic material Mix-O-Matic Blending causes phage protein coat to fall off Using S35 When centrifuged, phage protein coats remain in the supernatant while bacteria form a pellet The supernatant is radioactive, but the pellet is not. Did protein enter the bacteria? Is protein the genetic material?

  7. T2 grown in P32 containing media incorporate P32 into their DNA Bacteria grown in normal non-radioactive media T2 attach to bacteria and inject genetic material Mix-O-Matic Blending causes phage protein coat to fall off Using P32 When centrifuged, phage protein coats remain in the supernatant while bacteria form a pellet The pellet is radioactive, but the supernatant is not. Did DNA enter the bacteria? Is DNA the genetic material?

  8. OH Phosphate NH2 - P HO O Base H+ H O N N N N H CH2 5’ O 1’ 4’ Sugar 3’ 2’ OH H OH A NucleotideAdenosine Mono Phosphate (AMP) Nucleotide Nucleoside

  9. NH2 Thymine (DNA) Uracil (RNA) CH3 Adenine N N N N N NH O NH O O N O NH N O N N O N N N O NH2 NH2 Guanine Cytosine NH2 N N Purines Pyrimidines

  10. Cytosine N O O N N N N Guanine H H O N H N N N H H Base PairingGuanine And Cytosine - + + - - +

  11. H H + N - Adenine Thymine CH3 H - + N N N N N N O O N Base PairingAdenine And Thymine

  12. + H H + N - Adenine - - Cytosine N O N N N O N H H N N N Base PairingAdenine And Cytosine

  13. - + - Thymine CH3 H + + N N N N N O N O N Guanine O H N H H Base PairingGuanine And Thymine

  14. CH3 OH O NH2 H OH P HO O HN N N N O O N N CH2 O O CH2 O NH2 B A S E S HO P O H O N H2N O H O H P HO O N O N N NH O SUGAR-PHOSPHATE BACKBONE N N O H2O H2O NH2 N O O CH2 N O CH2 N O HN N O HO P H2N H O O H H P HO O O CH2 O O CH2 O O HO P OH H HO DNA

  15. - - AT - - CG - - GC - - TA - - 3.4 nm 1 nm - - - - GC TA - - CG - - AT - - - - AT - - CG - - GC - - 0.34 nm TA - - The Watson - Crick Model Of DNA Minor groove Major groove

  16. Origins of Replication 5’ 3’ 5’ 3’ 3’ 5’ 5’ 3’ 3’ 5’ 5’ 3’ 5’ 3’ 5’ 3’ 5’ 3’ 5’ 3’ Large Linear Chromosomes Have Many Origins Of Replication

  17. 3’ 5’ 5’ 3’ 3’ 5’ 3’ Primase - Makes RNA primers 5’ Single-strand binding proteins - Prevent DNA from re-annealing Lagging Strand 5’ 5’ 3’ 5’ RNA Primers DNA Polymerase 5’ 3’ Helicase - Melts DNA Leading Strand 5’ 3’ Extension - The Replication Fork Okazaki fragment

  18. DNA Pol. 5’ 3’ 3’ 5’ Okazaki Fragment RNA Primer DNA Pol. 5’ 3’ 3’ 5’ RNA Primer RNA and DNA Fragments 5’ 3’ 3’ 5’ RNA Primer Nick Extension - Okazaki Fragments DNA Polymerase has 5’ to 3’ exonuclease activity. When it sees an RNA/DNA hybrid, it chops out the RNA and some DNA in the 5’ to 3’ direction. DNA Polymerase falls off leaving a nick. Ligase The nick is removed when DNA ligase joins (ligates) the DNA fragments.

  19. The End

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