1. DNA Structure and Function

2. I. Experiments on DNA
A. Hershey and Chase: showed DNA, not protein, is the genetic material.
1952
DNA
Protein

3. Used X-ray diffraction to determine the structure of DNA.
I. Experiments on DNA
B. Rosalind Franklin
Used X-ray diffraction to determine the structure of DNA.
1952

4. II. DNA DNA = Deoxyribonucleic acid
Found only in the nucleus of the cell
Eukaryotic chromosomes contain DNA wrapped around proteins (proteins called histones).
Composed of nucleotides which are the basic building blocks of all nucleic acids

5. A. Nucleotide: subunit of nucleic acid.
II. DNA
A. Nucleotide: subunit of nucleic acid.
Three parts of a nucleotide:
1. Nitrogen base
2. Phosphate group
3. Simple sugar (ribose or deoxyribose)

6. II. DNA Four possible bases: A. Purines B. Pyrimidines
B. Nitrogen Base
Four possible bases:
Double Ringed
Adenine (A)
Guanine (G)
A. Purines
Single Ringed
Thymine (T)
Cytosine (C)
B. Pyrimidines

7. II. DNA
B. Nitrogen Base

8. 1. Adenine -Thymine (A - T) 2. Guanine - Cytosine (G - C)
II. DNA
C. Complementary base pairing (Chargaff’s Rule)
1. Adenine -Thymine (A - T)
2. Guanine - Cytosine (G - C)
i. Base Pairing:
Principle that hydrogen bonds in DNA form only between adenine and thymine and between guanine and cytosine.

9. D. Shape of DNA: Double Helix
II. DNA
D. Shape of DNA: Double Helix
Discovered by Watson and Crick
Sides formed by sugar and phosphate, connected by covalent bonds.
Rungs of ladder = nitrogen bases.
Double helix is held together by weak hydrogen bonds between the nitrogen bases - 2 bonds for A & T; bonds between G & C

10. Sugar and phosphate group held together by covalent bonds
II. DNA
D. Shape of DNA: Double Helix
T = Thymine
Pyrimidine (1 rings)
A = Adenine
Purine
(2 rings)
Sugar and phosphate group held together by covalent bonds
G = Guanine
Purine
(2 rings)
C = Cytosine
Pyrimidine
(1 rings)

11. D. Shape of DNA: Double Helix
II. DNA
D. Shape of DNA: Double Helix
The two sides of the molecule are anti-parallel to one another (5’ and 3’ ends).
Anti-parallel
a. 5’ carbon attaches to the phosphate
group
b. 3’ carbon attaches to the hydroxyl (OH)

12. a. Watson and Crick developed the double-helix model of DNA.
III. Shape of DNA: Double Helix
1953
b. Double Helix: coiled structure of double-stranded DNA in which strands linked by hydrogen bonds form a spiral configuration
a. Watson and Crick developed the double-helix model of DNA.
Watson and Crick

13. III. Shape of DNA: Double Helix