Post on 29-Dec-2015
Deoxyribose and Phosphate are in all nucleotides, but there are 4 different nitrogenous bases› Adenine› Guanine› Cytosine› Thymine
All nitrogenous bases contain rings
Adenine and Guanine contain 2 rings and are called Purines
Cytosine and Thymine contain 1 ring and are called Pyrimidines
Remember the phrase:› Pure As Gold
DNA History In 1953, Scientists
Watson and Crick made a model of DNA as a double helix – the spiral staircase shape.
When untwisted looks like a ladder
The sides of the ladder are the backbone and alternate with deoxyribose and phosphate
The bases bond the two strands in the middle
A purine always bonds with a pyrimidine so the length is the same
They are bonded together by hydrogen bonds
Complementary Base Pairing
Cytosine always bonds with Guanine› Hint: (C and G
are letters that look alike)
Adenine always bonds with Thyamine› Hint: (A and T
are letters made of straight lines)