DNA, or deoxyribonucleic acid, consists of 46 chromosomes each made of two strands forming a double helix that stores genetic information essential for controlling cellular activities. The basic building blocks of DNA, known as nucleotides, are composed of deoxyribose, phosphate, and nitrogenous bases which pair in specific ways (A-T, C-G). Key discoveries in the understanding of DNA's structure were made by Erwin Chargaff, Rosalind Franklin, and the duo of James Watson and Francis Crick.

1. DNA

2. DNA Structure DNA : D eoxyribo n ucleic a cid Each chromosome is made of one piece of DNA 46 chromosomes = 46 pieces of DNA DNA: 2 strands connected Shape of a twisted ladder The twisted ladder is called a DOUBLE HELIX

3. Function of DNA: Stores genetic information: genetic information makes you what you are - Controls all cell and body activities

4. Chromosome Structure Section 12-2

5. Nucleotides: Basic building blocks of DNA Nucleotides are made up of: Deoxyribose : a sugar Phosphate Nitrogen Base: Adenine = A Guanine = G Cytosine = C Thymine = T

6. Nucleotides and Pairing: A-T C-G The sugar and phosphate make the sides or rails of the double helix (ladder)

7. Structure of DNA Section 12-1

8. DNA complementary strands The 2 strands of DNA are represented by the sequence of nitrogen bases A T C G A A C G T T A T A G C T T G C A A T Write the complementary DNA strand: A T C G G G T T A A C G T A T C C

9. The People Behind 1. 1949: Erwin Chargaff discovers the rules of base pairing A-T C-G

10. 1952: Rosalind Franklin determined that the DNA molecule was a coiled spiral. They used a technique called X-ray diffraction

11. 3. 1953: James Watson (USA) and Francis Crick (UK) determine the exact structure of DNA. Received the Nobel Prize in 1962

12. Nucleic Acids Are made of: C (carbon), H (hydrogen) , O (oxygen) , N (nitrogen) , P (phosphates) .