DNA was discovered in 1869, but its structure and role as the genetic material was not understood until later breakthroughs in the 20th century. In 1953, Watson and Crick published their discovery of the double helix structure of DNA, with two strands coiled around each other and connected through complementary base pairing of adenine and thymine and cytosine and guanine. This breakthrough explained DNA's role in inheritance and provided the foundation for modern genetics and molecular biology.

1. DNA:
Structure and Function

2. Our understanding of DNA
2
1869
• Discovery of DNA
• F. Miescher
1883
• Chemical basis of
inherited traits
• A. Weismann & K.
Nageli
late 1920s
• "Transformation
Principle"
• F. Griffith
1944
• DNA is the
Genetic Material
• Avery, MacCleod,
McCarty
1950
• DNA really is the
Genetic Material
• Hershey and
Chase
1950
• In DNA samples,
equal quantities
of Adenine and
Thymine while
Guanine equal to
Cytosine
• E. Chargaff
1952
• Photo 51
• R. Franklin
1953
• Double Helix!
• J. Watson & F.
Crick
A=T
C=G
*The only names and dates you have to remember are Franklin, Crick, and
Watson and the year 1953.

3. Figure 7.2
Frederick Griffith
3

4. 4

5. Figure 7.3
5

6. Race to discover the structure of DNA
6
X-ray diffraction

7. Maurice Wilkins and Rosalind Franklin
7

8. Chargaff’s Rule
Erwin Chargaff
8
A=T
C=G

9. James Watson and Francis Crick
9

10. 10
Photo 51
By R. Franklin
1953 The Eagle
Pub, Cambridge

11. Double Helix!
11

12. Nobel Prize 1962
12
Wilkins Crick Watson

13. Figure 7.5
• Two strands
• Nucleotides
A. Phosphate
B. Deoxyribose sugar
C. Nitrogenous base
1. Adenine
2. Guanine
3. Thymine
4. Cytosine
• Antiparallel orientation
• Complementary Bases
• Purines pair with pyrimidines
• A-T and G-C
13
DNA Structure

14. 14

15. Cell
Nucleus
Chromosome
DNA wrapped
around histone
protein
DNA Gene
DNA Structure within a Chromosome
15

16. Compare and Contrast:
DNA and RNA
16

17. The Central Dogma of Gene Expression
17
Proposed by Francis Crick 1958

18. 18

19. 19

20. 20

21. 21