1.
“What is DNA?”

2.
What was known about
DNA?
• It could be found in almost
all cells
• It contained phosphorus in
the form of phosphate.

3.
What was known about
DNA?
• It contained a sugar,
deoxyribose.
• It contained 4 forms of nitrogen
containing bases; purines -
adenine and guanine and
pyrimidines - thymine and
cytosine.

4.
“#hat is the structure of DNA?”

5.
Maurice Wilkins Rosalind Franklin
Kings College, London

6.
James Watson and Francis Crick
Cambridge College, London

7.
Linus Pauling
Chemistry at California Institute of Technology
(Caltech)

8.
Nucleotide

9.
nucleotide monomer nucleotide
(sugar, phosphate and nitrogen polymer
base A, T, C orG) (chain)

10.
Erwin Chargaff
calculated a “rough
equivalent” between
adenine and thymine
molecules and between
cytosine and guanine
molecules.
adenine guanine thymine cytosine

11.
X-ray Crystallography right -hand
Rosalind Franklin’s photo 51 double helix

12.
Complementary Base Pairing
C-G and A-T

13.
Watson and Crick
with their model of DNA
double helix 1953

14.
DNA Replication or
Synthesis
• enzymes separate or unzip
the two strands (breaks the
H bonds)
• the two unwound strands
each become a template for
the new strands to be built
• the new nucleotides are
paired and inserted
• enzymes “proofread the
new strands and seals the
base pair