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MOLECULAR GENETICS

MOLECULAR GENETICS. THE CHEMICAL NATURE OF THE GENE. © 2007 Paul Billiet ODWS. What does a gene do?. The must be able to hold information and decode it (translate it) into an organism as it grows and develops

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MOLECULAR GENETICS

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  1. MOLECULAR GENETICS THE CHEMICAL NATURE OF THE GENE © 2007 Paul Billiet ODWS

  2. What does a gene do? • The must be able to hold information and decode it (translate it) into an organism as it grows and develops • It must be able to copy itself so that it can be passed on to future generations © 2007 Paul Billiet ODWS

  3. What does a gene look like? • It must be a big moleculeto hold the large amount of information required to build an organism • It must be a complex moleculeto provide the necessary variation to code the instructions that control growth and development © 2007 Paul Billiet ODWS

  4. Four classes of molecules which could form genes Biological macromolecules Elements Building Blocks Polysaccharides (carbohydrates) CHO Monosaccharides Lipids (Fats, oils and waxes) CHO Fatty acids (and glycerol) Polypeptides (proteins) CHONS Amino acids Polynucleotides (Nucleic acids) CHONP Nucleotides © 2007 Paul Billiet ODWS

  5. Griffiths (1928) Tried to determine what genetic material was made of. National Library of Medicine's Profiles in Science © 2007 Paul Billiet ODWS

  6. Pneumococcus bacteria on mice 2 STRAINS R-type Rough colonies Avirulent S-type Smooth colonies Virulent Innoculate into mice Innoculate into mice Deadfrom pneumonia Not killed Griffiths’ Experiment © 2007 Paul Billiet ODWS

  7. Griffiths’ Experiment EXPERIMENT Live R-type (harmless) + Heat-killed S-type CONTROL Live R-type only CONTROL Heat-killed S-type only Mice died from pneumonia No mice died No mice died Further test: Cultured lung fluid Live S-type found © 2007 Paul Billiet ODWS

  8. Conclusion • Transformation of R-type to S-type • Transformation was brought about by some heat stable compound present in the dead S-type cells Called the TRANSFORMING PRINCIPLE © 2007 Paul Billiet ODWS

  9. Avery, MacCleod & McCarthy (1944) Tried purifying the transforming principle to change R-type Pneumococcus to S-type National Library of Medicine's Profiles in Science © 2007 Paul Billiet ODWS

  10. Results The compound that had the most effect was: • Colourless, viscous and heat stable • It contains phosphorus • It was not affected by trypsin (a protease) or amylase. • It was inhibited by RNAase and DNAase Conclusion The transforming principle is a nucleic acid © 2007 Paul Billiet ODWS

  11. Live R-type + DNAextracted and purified from S-type bacteria Experiment Mice died from pneumonia Live S-type bacteria cultured from the lung fluid These S-type bacteria remained virulent for generation after generation © 2007 Paul Billiet ODWS

  12. Conclusion DNA is the transforming principle and it is hereditary material Criticism The DNA was not totally pure It was contaminated by a small amount of protein This protein could be the real transforming principle BUT When Avery and his team prepared purer extracts of DNA they became better at transforming the bacteria types © 2007 Paul Billiet ODWS

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