• Where is DNA located within a cell?
• Why is DNA important?

• Nucleotides are the building blocks of DNA.
• Each nucleotide contains a phosphate group , a five carbon sugar, and a nitrogen base.
• The five carbon sugar is called deoxyribose.
• The full name of DNA is deoxyribonucleic acid

• Every nucleotide has the same sugar molecule and phosphate group, but each nucleotide contains one of four nitrogen bases.

The four nitrogen bases that make up DNA are adenine, guanine, cytosine, and thymine.
• Adenine and Guanine are called purines. Purines have 2 rings of carbon and nitrogen atoms.
• Thymine and Cytosine are called pyrimidines.
Pyrimidines have a single ring of carbon and nitrogen atoms.

• 1949-Erwin Chargaff showed that in DNA, the number of adenines equal the number of thymines , AND the number of cytosines equal the number of guanines. However, the amount of each nucleotide was not the same among different organisms.
• Base pairing rule: Adenine will always pair with
Thymine ; and Cytosine will always pair with
Guanine .

• Rosalind Franklin and Maurice Wilkins used X ray diffraction to take first picture of DNA. Determined a two dimensional picture of DNA’s structure.

• James Watson and Francis Crick – 3-D shape of DNA being 2 strands of nucleotides that form a spiral staircase or double helix .
• DNA is a twisted ladder with alternating patterns of phosphates and sugars making the sides of the ladder, and each rung being a purine/pyrimdine pair held together by hydrogen bonds.
• The base pair rules tell us what the rungs can be, A and T or G and
C
• Each strand of the double helix is complementary to each other; the sequence of 1 strand determines the sequence of the other.

Each strand of the double helix is complementary to each other; the sequence of 1 strand determines the sequence of the other.
Strand One - T C G A A C T
Strand Two -