Watson and Crick - X-Ray data conforming models led to the double helix.

1953 - They used other evidence and Franklin's X-Ray diffraction photo to conclude that DNA is composed of 2nucleic acid chains (or strands) bonded through their basis (like a ladder) and twisted into a double helix.

Pg 308 - 310 Study Work Sheet and figures 16.5 & 16.7

The pairs of nitrogenous bases of Adenine, Thymine, Quanine and Cytosine are connected by hydrogen bonds. 

Within a species the amount of Adenine equals the amount of Thymine and the amount of Guanine equals the amount of Cytosine: A<-->T & G<-->C

the percentage of A, T, C and G varied between species and was constant within a species

DNA Replication

The copying of the double stranded DNA molecule, producing two identical DNA double helices.

Two things it had to do to be the Genetic material:

1. Carry information from generation to gen-It does this through the order of specific base sequences

2. Replicate itself - it accomplishes this through the separation f the 2 strands and using each one as a template to build a new strandon itself by using complementary base pairing of A w/ T and C w/ G.

Base pairing: A-T and G-C  (Chargaff's Rule)

Elongating DNA