Class Notes
Discovering the
structure of DNA
Questions/Main Idea:
Name: _______________________________________
Period:_______________________________________
Date: _______________________________________
Notes:
What is DNA?
• DNA = deoxyribonucleic acid
• Holds all our cell’s information
• Located in the cell’s nucleus
What we already know
about DNA
• Codes for proteins essential to life
• A nucleic acid macromolecule
• Monomer of a nucleic acid is a nucleotide
• The three parts of a nucleotide:
– 1. Phosphate group
– 2. Sugar (deoxyribose)
– 3. Nitrogen base
Nitrogen bases
• The nitrogen base can either be a purine or a pyrimidine.
• How many carbon rings does each have?
– Purines have 2
– Pyrimidines have 1
• DNA has 4 nitrogen bases:
– Thymine (T)
– Adenine (A)
– Cytosine (C)
– Guanine (G)
• Adenine and Guanine are purines
Cytosine and Thymine are pyrimidines.
A collaborative effort!
• In the early 1900s, it was known that information had to be passed
from cell to cell. However, it was not known what was responsible
for carrying this information.
• Some scientists thought that it must be protein, others that it was
the nucleic acid.
• Three major experiments helped show that it was a nucleic acid:
– Griffith
– Avery-MacLeod-McCarty
– Hershey-Chase
Frederick Griffith got
lucky?
• Griffith studied pneumonia bacteria
• In 1928, he isolated two strains of
bacteria, and injected them into mice
– Live R strain was harmless (mice lived)
– Live S strain caused pneumonia (mice died)
– When he injected the S Strain that was heat-killed, the mice
lived
• BUT.... When he mixed the live R strain with the heat-killed S
strain and injected into mice, the mice died.
Griffith's Conclusions
• When the heat-killed bacteria mixed with the live harmless
bacteria, something was exchanged between them, making the live
harmless bacteria deadly
• Transformation = process in which one strain of bacteria changes
the gene(s) of another bacteria
