1. DNA: Blueprint for Life
The Structure of DNA A. Nucleotides – basic unit of DNA
B. Nitrogen Bases
C. DNA Replication

2. Structure of DNA DNA made of nucleotides, the basic unit
Nucleotide is made of three parts:
1. One Phosphate
2. One 5-Carbon Sugar (deoxyribose)
3. One Nitrogen base
Adenine(A), Guanine(G) – Purines
Thymine(T), Cytosine(C) – Pyrimidines

3. Structure of DNA Sugar and Phosphate are the “backbone” of DNA
Two parallel strands of sugar-phosphate groups with pairs of nitrogen bases linking the two strands together with weak hydrogen bonds, forming a double helix.
WHY WEAK BONDS?

4. Structure of DNA Nitrogen Base Pairing- Chargoff’s Rules:
A=T (one purine/ pyrimidine)
C=G (one purine/ pyrimidine)
DNA strands are complementary because of base pairing rules
Nitrogen bases are attached to
sugars.

5. DNA Nucleotides Purines Pyrimidines Deoxyribose Phosphate group
Adenine
Guanine
Cytosine
Thymine
Phosphate group
Deoxyribose

6. Structure of DNA Nucleotide Weak Hydrogen bonds
Sugar-phosphate backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)

7. Molecular Structure

8. Chromosome Structure Nucleosome Chromosome DNA double helix Coils
Supercoils
Histones

9. DNA Replication A Perfect Copy
When a cell divides, each daughter cell receives a complete set of chromosomes. This means that each new cell has a complete set of the DNA code. Before a cell can divide, the DNA must be copied so that there are two sets ready to be distributed to the new cells.

10. DNA Replication
Complementary strands of DNA serve as a pattern for a new strand.
DNA replication carried out by enzymes which “unzip” the two strands by breaking the hydrogen bonds.
Then, appropriate nitrogen bases are inserted. Enzymes also proofread the bases to make sure of correct base pairing.

11. DNA Replication Original strand DNA polymerase New strand Growth
Replication fork
Replication fork
Nitrogenous bases
New strand
Original strand

12. DNA Replication DNA 3’G C C A T T G T A A T5’
enzymes
Copied DNA 5’C G G T A A C A T T A3’
DNA 5’C G G T A A C A T T A3’
Copied DNA 3’G C C A T T G T A A T5’