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DNA and RNA
Chapter 12
Griffith and Transformation
Griffith hypothesized…
• when the live, harmless bacteria and
the heat-killed bacteria were mixed,
some factor was transferred from
the heat-killed cells into the live cells
• The ability to cause disease was
inherited by the transformed
bacteria’s offspring, the transforming
factor might be a gene
Avery and DNA
• Avery and colleagues made an extract
from the heat-killed bacteria then
treated it with enzymes that destroyed
proteins, lipids, CHOs, and RNA
• Transformation still occurred
• When DNA was destroyed,
transformation did not occur
• DNA stores and transmits the genetic
information from one generation of an
organism to the next
**The Hershey-Chase Experiment
Hershey and Chase concluded…
•the genetic material
of the bacteriophage
was DNA, not protein
The Structure of DNA
nucleotides
deoxyribose
Phosphate
Nitrogen
group
base
Nitrogen Bases
Chargaff’s Rules
[A] = [T] and [G] = [C]
X-Ray Evidence
• Rosalind Franklin used x-ray diffraction to
learn about the structure of DNA
The Double Helix
• F. Crick and J. Watson (1953)
• 2 strands wound together
• Hydrogen bonds form between certain
bases with just enough force to hold 2
strands together
A ---- T
G ---- C
Base pairing principle explained Chargaff