1. DNA

2. A Few Questions
What organelle is known at the “control center” of the cell?
Nucleus
What structures are found in the nucleus?
Chromosomes
What are located on chromosomes?
Genes

3. A Few More What are chromosomes composed of?
DNA
How do genes and chromosomes control the activity of a cell?
By producing proteins that regulate cellular functions.

5. DNA Components & Structure
Long molecule made of nucleotides
Nucleotides: 5-carbon sugar, a phosphate, & nitrogenous base
Four kinds of nitrogenous bases

6. Types of Bases in DNA Two types of bases: pyrimidines and purines.
Pyrimidines: Cytosine (C) & Thymine (T)
Purines: Adenine (A) & Guanine (G)
These bases carry the genetic code.

7. Base Pairing
Chargaff discovered that DNA molecules contain equal numbers of G&C bases and A&T bases.
A always pairs with T
G always pairs with C

8. Rosalind Franklin
Used X-ray evidence to get information about DNA’s structure.
The strands of DNA are twisted around each other, in a helix.
The bases are near the
center of the molecule.

9. Franklin

10. Watson & Crick
With the use of Franklin’s work, they developed a structured model.
The model was a double helix, in which two strand were wound around each other.
The model explained how DNA could carry information, and how it could be copied.

11. Watson & Crick

12. Double Helix Looks like a twisted ladder or a spiral stair case.
Hydrogen bonds hold the two strand together.