1. DNA and the Code of Life Biology 11: Section 6.1

2. Learning Goals Students will complete dihybrid crosses Students will use product law to predict offspring traits Students will know the difference between discontinuous and continuous variation

3. History of the Discovery of DNA 1831: nucleus discovered 1865: Mendel published his findings 1882: mitosis described by Walter Fleming 1882: Edouard van Benden noticed egg/sperm cells had half the chromosome number 1887: Miescher found something he called nuclein in the nucleus of cell 1887: August Weismann explained “meiosis”

4. History of the Discovery of DNA 1900: significance of Mendel’s experiments understood 1902: Walter S. Sutton and Theodor Boveri independently confirm Mendel’s Law of Segregation and independent assortment – Sutton hypothesized that chromosomes carry genes 1930s: Joachim Hammerling verified the genetic material was in the nucleus 1951: Franklin and Wilkins discovered helical shape of DNA 1952: Hershey and Chase prove DNA as genetic material 1953: Watson and Crick: First model of DNA

5. Watson and Crick DNA Model James Watson and Francis Crick determined the way the components of DNA were arranged (structure) Determined the amount of adenine in DNA always equaled thymine; guanine equaled cytosine Rosaline Franklin, working with Maurice Wilkins confirmed the helical structure

6. What’s DNA Made of? Protein and nucleic acids in equal parts Recall: DNA is located in the nucleus, contains the instructions that ensure genetic continuity, and is found in every living organism DNA is the only molecule that can replicate itself (unlike proteins, lipids and sugars); this means cells can replicate DNA controls protein production to control the expression of traits in an organism

7. DNA is a very large nucleic acid molecule that is in the shape of a helix or corkscrew The molecule is a polymer of nucleotides (the basic repeating subunit) Nucleotides are made of a phosphate group, a 5 carbon sugar (deoxyribose) and one of four different nitrogenous bases (adenine, thymine, guanine, cytosine)

8. Components of DNA purines pyrimidines

9. The Structure of DNA Double helix (like a spiral ladder) Double stranded Nitrogenous bases form the “rungs” Sugar and phosphate groups alternate to form the backbone Bases from one side are paired in a specific way to bases on the other side attracted by hydrogen bonds

10. Hydrogen Bonding Between Bases Hydrogen bonds are relatively weak bonds H bonds only form between complementary base pairs The backbone of the DNA molecules becomes twisted, forming a spiral ladder (helix) A pairs with T with 2 H bonds, C pairs with G with 3 H bonds

11. Variations in the DNA Code The nucleotide bases (ATCG) in different combinations make an organism’s genetic code Base are “read” in set of three (i.e. ATT) called codons or triplet code These codons code for amino acids, which are the building blocks of proteins Amino acids can be organized in many different ways to give rise to all the different proteins that exist

15. To Do: Read section 6.1 Complete questions 2, 4, 5, 7 on page 233 Draw and label a model of DNA