1. Deoxyribonucleic acid
Structure and Function

2. Components of DNA Sugar = Deoxyribose Phosphate = PO43-
Ribose is missing hydroxyl group (-OH) from 2’C
Phosphate = PO43-
Links to the either its 3’C or its 5’C
Water (HOH) is lost in the condensation reaction
Nitrogenous base
Attaches to the 1’C of the deoxyribose
Purine (2-ring structure) = Adenine & Guanine
Pyrimidine (single-ring) = Thymine & Cytosine

3. Structure

4. Complementary Base Pairing
Chargaff’s Rules
Noticed % thymine = % adenine
Noticed % cytosine = % guanine
Single-ringed pyrimidine pairs with double-ringed purine
Guanine (purine) : cytosine (pyrimidine)
Held together with 3 hydrogen bonds
Adenine (purine) : thymine (pyrimidine)
Held together with 2 hydrogen bonds

5. Double Helix The leading strand goes 5’ (five prime) to 3’
The lagging strand goes 3’(three prime) to 5’
Hydrogen bonding links the 2 strands
Convention allows sequences to be shown with single-letter abbreviations of nucleotides
5’ T A C C C G A T T C G C C G G A A A T A C G A 3’
3’ A T G G G C T A A G C G G C C T T T A T G C T 5’

6. History
James Watson , Francis Crick, & Maurice Wilkins won Nobel Prize in Medicine (1962) for elucidation of DNA structure (double helix)
Nucleotides H-bond with opposite strand
They relied on Wilkins’ & Rosalind Franklin’s x-ray diffraction studies of DNA
Diffraction is a wave property seen when waves bend when passing by/ around edge of objects.

7. 4-stranded DNA 2-stranded DNA
4-stranded DNA
2-stranded DNA

8. Replication
In order to be replicated, each origin of replication must be bound by: an Origin Recognition Complex of proteins (ORC). These remain on the DNA throughout the process.
Accessory proteins called licensing factors. These accumulate in the nucleus during G1 of the cell cycle. They include:
Cdc-6 and Cdt-1, which bind to the ORC and are essential for coating the DNA with
MCM proteins. Only DNA coated with MCM proteins (there are 6 of them) can be replicated

9. DNA Replication http://users. rcn. com/jkimball. ma