1. p. 348 A.Q. 1a, 2ab, 3ab

2. 1a. List the chemical components of DNA. 1a. The chemical components of DNA are deoxyribose, phosphate groups, and four different nitrogenous bases. 2a. Describe the discoveries that led to the modeling of DNA. 2a. Chargaff discovered base pairing rules. Franklin took X-ray photographs that revealed that DNA has a spiral structure. This finding helped Watson and Crick understand DNA’s structure.

3. p. 348 A.Q. 1a, 2ab, 3ab 2b. Why did scientists have to use tools other than microscopes to solve the structure of DNA? 2b. Scientists had to use tools other than microscopes because DNA is too small to be seen with light microscopes, the only type available at the time. 3a. Describe Watson and Crick’s model of the DNA molecule. 3a. Watson and Crick’s model is composed of two strands that are connected by bonds between nitrogen bases. 3b. Did Watson and Crick’s model account for the equal amounts of thymine and adenine in DNA? Explain. 3b. Yes; Watson and Crick’s model depicted DNA as a double helix with adenine and thymine paired together. This pairing accounts for the equal amounts of thymine and adenine in DNA.