1. DNA Structure
Section 11.2

2. Nucleic Acids (2 groups)
DNA
Deoxyribonucleic acid
Stores genetic info
Nucleic Acid made of nucleotides
ONLY 4 types of nucleotides make up DNA
RNA
Ribonucleic acid
Plays key role in cells (Details to come…)

3. Nucleotides Each nucleotide has 3 parts
1. ring-shaped sugar called deoxyribose
2. A phosphate group (phosphorous surrounded by 4 oxygens)
3. Nitrogen base: single or double ring of carbon & nitrogen atoms w/ functional groups

4. Nitrogen Bases Pyrimidines Purines Single ringed Thymine (T)
Cytosine (C)
Purines
Double ringed
Adenine (A)
Guanine (G)

5. DNA Strands To make a strand of DNA:
The nucleotides are joined together w/ a covalent bond connecting the sugar of one nucleotide to the phosphate group of the next
This makes up the “Backbone” of DNA (sides of the ladder)

6. DNA’s Structure
Rosalind Franklin & Maurice Wilkins produced photos of DNA using X-ray crystallography
Gives clues to shapes & dimensions
Showed DNA to be a helix

7. The Double Helix
James Watson & Francis Crick created a model w/ the assistance of Franklin’s photos:
2 strands of nucleotides wound around each other forming a DOUBLE HELIX
Hypothesized the nitrogen bases across from each other formed hydrogen bonds

8. Complementary Base Pairs
The structure of the nitrogen bases determine specific pairings b/w the nucleotides
sizes & ability to form H-bonds
A always pairs w/ T (complementary bases)
G always pairs w/ C (complementary bases)
The sequence on one strand can vary: the sequence of the bases on the 2nd strand are determined by the first.

9. Concept Check 11.2
What are the three parts of a nucleotide? Which parts make up the backbone of a DNA strand?
List the two base pairs found in DNA.
If six bases on one strand of a DNA double helix are AGTCGG, what are the six bases on the complementary section of the other strand of DNA?