Powerpoint Presentation: Molecular Genetics
Transcript of Powerpoint Presentation: 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
It must be able to copy itself so that it can be passed on to future generations
© 2007 Paul Billiet ODWS
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
© 2007 Paul Billiet ODWS
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)
Building BlocksElementsBiological macromolecules
© 2007 Paul Billiet ODWS
Griffiths (1928)
Tried to determine what genetic material was made of.
National Library of Medicine's Profiles in Science
© 2007 Paul Billiet ODWS
Griffiths’ ExperimentPneumococcus bacteria on mice
2 STRAINS
S-typeSmooth colonies
Virulent
R-typeRough colonies
Avirulent
Innoculate into mice Innoculate into mice
Dead from pneumonia
Not killed
© 2007 Paul Billiet ODWS
Griffiths’ Experiment
Live S-type found
Further test: Cultured lung fluid
No mice diedNo mice diedMice died from pneumonia
CONTROLHeat-killed S-type
only
CONTROLLive R-type only
EXPERIMENTLive R-type (harmless)
+Heat-killed S-type
© 2007 Paul Billiet ODWS
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
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
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
© 2007 Paul Billiet ODWS
Experiment
Mice died from pneumonia
Live R-type+
DNA extracted and purified from S-type bacteria
These S-type bacteria remained virulent for generation after
generation
Live S-type bacteria cultured from the lung fluid
© 2007 Paul Billiet ODWS
Conclusion
DNA is the transforming principle and it is hereditary materialCriticismThe DNA was not totally pureIt was contaminated by a small amount of proteinThis protein could be the real transforming principleBUTWhen Avery and his team prepared purer extracts of DNA they became better at transforming the bacteria types
© 2007 Paul Billiet ODWS