Download Evidence for DNA Structure and Function

Evidence for DNA Structure
and Function
TIMELINE OF IMPORTANT EXPERIMENTS
Timeline – Important Discoveries
• Griffith
1928 • Transformation – good cells turned bad
• Avery, McCarty, Macleod
1944 • DNA is the transforming factor
• Chargaff
1950 • A-T and C-G ratios
1951
• Franklin
• X-ray diffraction photos of DNA
• Chase and Hershey
1952 • Radioactive viruses show DNA is hereditary molecule
• Watson and Crick
1953 • Develop 3-D structure of DNA
Evidence for DNA Structure/Function
!  Griffith (1928)
!  Harmless bacteria
could be
transformed by a
‘factor’ found in
harmful bacteria
Evidence of DNA Structure/Function
!  Avery, et al. (1944)
!  Repeated Griffith’s
experiment to determine
the transforming ‘factor’
!  Using enzymes to
destroy DNA, RNA and
proteins
!  Mice survived when
DNA was destroyed
Evidence for DNA Structure/Function
!  Chargaff (1950)
!  Determined equal ratios
of adenine and thymine
in any given DNA
sample
!  Determined equal ratios
of cytosine and guanine
in any given DNA
sample
Evidence for DNA Structure/Function
!  Franklin (1951)
!  Used X-ray
diffraction through
crystallized DNA
!  Indicated spiral
structure
!  Consistent diameter
and cross-connectors
Evidence for DNA Structure/Function
!  Hershey and Chase (1952)
!  Bacteriophage virus – protein coat
labeled with radioactive sulfur; DNA
with radioactive phosphorus
!  After infection, separate bacteria
from virus and look for radioactivity
!  If S-35 is with bacteria = protein has
caused transformation
!  If P-32 is with bacteria = DNA has
caused transformation
Evidence for DNA Structure/Function
!  Hershey and Chase (1954)
!  P-32 with bacteria confirms DNA as the ‘factor’
Evidence for DNA Structure/Function
!  Watson and Crick
(1953)
!  Used evidence from
Franklin, Chargaff and
others to determine
detailed chemistry of
DNA