Download GENETICS 603 Outline and Key Topics for Lecture 1 DNA

GENETICS 603 Outline and Key Topics for Lecture 1 DNA
Genes are made of DNA
1928 Griffith showed that a mixture of heat-killed Siii bacteria
and Rii live bacteria could lead to pneumonia in mice and
recovery of live Siii colonies from lungs. Since neither the boiled
Siii or Rii bacteria alone could cause disease, he concluded that
the genetic information needed to make the Siii-type
polysaccharide shell was "transforming" the Rii bacteria; that is
changing their genotype to allow them to make the Siii
polysaccharide
1944 Avery, MaCleod and McCarty showed that DNA could cause
the transformation; treatment with protease to destroy protein
did not eliminate transformation, but treatment with DNAase
did. Thus, they had succeeded in showing that the "transforming
principle" (the agent that caused transformation) is DNA.
1952 Hershey and Chase showed that the DNA packed into the
head of bacteriophage T2 is required for phage reproduction and
is present in progeny, but that the protein components are not.
(They took advantage of radioisotopes to differentially label DNA
and protein. )
1956 Fraenkel-Conrat showed that the RNA present in TMV, not
the protein coat, determined the type of progeny produced.
The structure of DNA
1947 Chargaff showed that different species have different
amounts of the4 nucleotides that make up DNA, but in all cases,
within the limits of experimental error, the amount of A was
equal to the amount of T, and that G = C. Thus the ratio of
purines (A&G) to pyrimidines (T&C) in DNA is 1
X-ray diffraction studies by Wilkins and Franklin showed that
DNA exists in a helix.
1953 Watson and Crick published the "double helix" model of
DNA in which two strands, running in opposite directions, were
held together by Hydrogen bonds between the base pairs A and T,
and G and C. The base pairs are in the center of the molecule like
the steps of a spiral staircase, with the phosphate-sugar
(deoxyribose) backbones of the two strands forming the frame.
1957 Meselson and Stahl used non-radioactive isotopes (N-14 and
N-15) to show that DNA replication fits a semi-conservative model
as predicted by the Watson-Crick double helix.
If you have access to a computer with a 4.x or later version of Netscape or
Explorer you can get a good dynamic view of DNA structures from at
http://molvis.sdsc.edu/dna/