1. Deoxyribonucleic acid Structure and Function

2. Components of DNA • Sugar = Deoxyribose • Ribose is missing hydroxyl group (-OH) from 2’C • Phosphate = PO43- • Links to the sugar @ 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 CC G A T T C G C C G G A AA T A C G A 3’ • 3’ A T G GG C T A A G C G G C C T TT 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. http://news.yahoo.com/genetic-twist-4-stranded-dna-lurks-human-cells-124030861.htmlhttp://news.yahoo.com/genetic-twist-4-stranded-dna-lurks-human-cells-124030861.html 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 Replicationhttp://users.rcn.com/jkimball.ma.ultranet/BiologyPages/D/DNAReplication.html