DNA controls the activities of cells and carries genetic information. It is found in the nucleus of cells. In 1953, James Watson and Francis Crick discovered that DNA has a double helix structure with alternating sugar and phosphate molecules forming the backbone and four nitrogen bases - adenine, guanine, cytosine, and thymine - bonding between the strands in a specific pattern with adenine bonding to thymine and guanine bonding to cytosine. DNA is made up of small repeating units called nucleotides, each containing a sugar, phosphate, and one of the four nitrogen bases.

1. CHAPTER 9 & 10 NOTES DNA STRUCTURE & FUNCTION

2. What is DNA? Nucleic acid – a compound composed of a 5-carbon sugar, a nitrogen base, and a phosphate. Deoxyribonucleic acid – DNA – controls the cells activities, carries genetic information. It is found in the nucleus of the cell.

4. Who discovered DNA? DNA was discovered in the late 1940’s, but the structure was not discovered until 1953 . Two scientists named James Watson and Francis Crick came up with a model of the structure of DNA.

5. What does Watson and Crick’s DNA model look like? The shape looks like a twisted ladder – double helix . Each side is made up of alternating sugar and phosphate molecules. The sugar in DNA is called deoxyribose. Attached to each sugar is a nitrogen base . To make the ladder complete, each base is joined by a weak hydrogen bond to a base on the other side.

6. DNA double helix

7. What are the nitrogen bases? There are 4 different nitrogen bases in DNA: 1. guanine - G 2. thymine - T 3. adenine - A 4. cytosine - C

8. How do the bases bond? The nitrogen bases always bond in the same way: adenine to thymine A - T guanine to cytosine G - C

9. Base Pairing

11. How are these parts put together? DNA is built up in small units. Each unit is made up of a sugar , a phosphate , and a nitrogen base . This small unit is called a nucleotide .