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8/8/2019 01 Molecular Genetics
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MOLECULAR
GENETICS
THE CHEMICAL NATURE OFTHE GENE
2007 Paul Billiet ODWS
8/8/2019 01 Molecular Genetics
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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
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What does a gene look like?
It must be a big molecule
to hold the large amount of information required
to build an organism
It must be a complex molecule
to provide the necessary variation to code the
instructions that control growth and development
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Four classes of molecules
which could form genes
NucleotidesCHONPPolynucleotides
(Nucleic acids)
Amino acidsCHONSPolypeptides(proteins)
Fatty acids (and
glycerol)
CHOLipids
(Fats, oils and waxes)
MonosaccharidesCHOPolysaccharides(carbohydrates)
BuildingBlocksElementsBiological
macromolecules
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Griffiths (1928)
Tried to determine what
genetic material was
made of.
National Library of Medicine's Profiles in Science
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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 TRANSFORMINGPRINCIPLE
2007 Paul Billiet ODWS
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Avery, MacCleod & McCarthy
(1944)
Tried purifying the
transforming principle to
change R-typePneumococcus to S-type
National Library of Medicine's Profiles in
Science
2007 Paul Billiet ODWS
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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
ConclusionThe transforming principle is a nucleic acid
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Experiment
Mice died from
pneumonia
Live R-type+
DNA extracted and purifiedfrom S-type bacteria
These S-type bacteria remained
virulent for generation after
generation
Live S-type bacteria cultured
from the lung fluid
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Conclusion
DNA is the transforming principle and it is hereditarymaterial
CriticismThe DNA was not totally pure
It was contaminated by a small amount of protein
This protein could be the real transforming principle
BUTWhen Avery and his team prepared purer extracts of DNAthey became better at transforming the bacteria types
2007 Paul Billiet ODWS
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