01 Molecular Genetics

8/8/2019 01 Molecular Genetics

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MOLECULAR

GENETICS

THE CHEMICAL NATURE OFTHE GENE

2007 Paul Billiet ODWS


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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



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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



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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


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01 Molecular Genetics