1. Structure & Replication
Deoxyribonucleic acid
DNA
Structure & Replication

2. “A Winding Staircase”
DNA is a long molecule that is shaped like a spiral staircase
It is composed of two parallel strands of subunits
Known as a double helix

3. Nucleotides Nucleotides are the subunits that make up DNA
Each nucleotide is made up of three parts:
Sugar & Phosphate make up “back bone” (hand rails of the staircase)
The Nitrogen Bases pair together to connect the strands (steps of the staircase)
1.) Sugar
2.) Phosphate
3.) Nitrogen Base

4. Nitrogen Bases
In DNA, each nucleotide has the same sugar molecule and phosphate group, but it can have one of 4 bases
Adenine
Thymine
Cytosine
Guanine
The base-pairing rules state that
Adenine only pairs with Thymine (complementary)
Cytosine only pairs with Guanine (complementary)
Base pairs are held together by hydrogen bonds

5. How do cells make more DNA?
Remember that before mitosis or meiosis can occur, DNA must be copied!!
This process is called REPLICATION
Steps of DNA replication
An enzyme (helicase) unwinds & separates the 2 strands of DNA
New complementary nucleotides are added to each side
Another enzyme (DNA polymerase) joins the newly added nucleotides together and “proof-reads” the new strands