12 – 1 DNA

Gene – is a portion of DNA that codes for a specific Trait DNA – Genetic material of living organisms and is located in the chromosomes of each cell. Gene – is a portion of DNA that codes for a specific Trait A. DNA is made of two chains of repeating subunits called nucleotides - B. Each nucleotide consists of three parts: 1. Deoxyribose: a 5-carbon sugar molecule 2. A phosphate group: made of P surrounded by oxygen 3. Nitrogenous base: basic molecule that contains nitrogen

2. Four nitrogenous bases A. Purines (2 carbon rings) 1. Adenine = A 2. Guanine = G B. Pyrimadines (1 carbon ring) 1.Cytosine = C 2. Thymine = T

3. The Double Helix A. Made of two nucleotide chains that wrap around each other to form a spiral staircase. B. Backbone - Alternating sugar and phosphate groups. C. Rungs - Hydrogen bonds hold opposing bases to each other, perpendicular to backbone.

A. Base-pairing rules: B. One purine bonds with one pyrimadine 4. Complementary Base Pairing A. Base-pairing rules: 1.Cytosine always bonds with guanine a.3 hydrogen bonds b. C - G 2. Adenine always bonds with thymine a. 2 hydrogen bonds b. A - T B. One purine bonds with one pyrimadine