The discovery that DNA is the genetic code involved many experiments.

Transcription

1 Section 1: The discovery that DNA is the genetic code involved many experiments. K What I Know W What I Want to Find Out L What I Learned

2 Essential Questions Which experiments led to the discovery of DNA as the genetic material? What is the basic structure of DNA? What is the basic structure of eukaryotic chromosomes?

3 Vocabulary Review nucleic acid New double helix nucleosome

4 Discovery of the Genetic Material After the rediscovery of Mendel s work, scientist began to look for the molecule involved in inheritance. For many years, scientists struggled to determine if DNA or protein was the source of genetic information.

5 Discovery of the Genetic Material Griffith First major experiment searching for the genetic material Involved transformation between two forms of S. pneumoniae Set the stage for the search to identify the transforming substance

6 Discovery of the Genetic Material Avery Identified the molecule that transformed the R strain of S. pneumoniae into the S strain Concluded that when the S cells were killed, DNA was released R bacteria incorporated this DNA into their cells and changed into S cells

7 Discovery of the Genetic Material Hershey and Chase Used radioactive labeling to trace bacteriophage DNA and protein. Concluded that the bacteriophage DNA was injected into the cell and provided the genetic information needed to produce new viruses.

8 Summary of Hershey-Chase Results Interactive Table FPO Add link to interactive table from page 328 (table 1) here.

9 DNA Structure Nucleotides Nucleotides are the subunits of nucleic acids, and consist of 5-carbon sugar Phosphate group Nitrogenous base

10 DNA Structure Chargaff Analyzed the amount of A, G, T, and C in the DNA of various species Chargaff s rule: C = G and T = A

11 DNA Structure The structure question Search for the structure of DNA was lead by four scientists: Rosalind Franklin, British chemist Maurice Wilkins, British physicist Francis Crick, British physicist James Watson, American biologist

12 DNA Structure X-ray diffraction X-ray diffraction techniques indicated that DNA was a double helix, or twisted ladder shape. The double helix shape was formed by two strands of nucleotides twisted around each other.

13 DNA Structure Watson and Crick Using Franklin and Chargaff s data, Watson and Crick measured the width of the helix and the spacing of the bases. They built a model that conformed the Franklin and Chargaff s data.

14 DNA Structure DNA structure DNA often is compared to a twisted ladder. Rails of the ladder are represented by the alternating deoxyribose and phosphate. The pairs of bases (cytosine-guanine or thymine-adenine) form the steps. Purine base always binds to a pyrimidine base

15 DNA Structure Orientation DNA molecules have specific orientations of the two strands On the top rail, the strand is said to be oriented 5 to 3. The strand on the bottom runs in the opposite direction and is oriented 3 to 5.

16 Structure of DNA Animation FPO Add link to animation from page 331(Figure 8) here.

17 Chromosome Structure In prokaryotes, DNA molecules are contained in the cytoplasm, and consist mainly of a ring of DNA and associated proteins. In eukaryotes, DNA is organized into individual chromosomes.

18 Chromosome Structure To fit into a cell, DNA coils around a group of beadlike proteins called histones. DNA + histones form a nucleosome, which group together into chromatin fibers, which supercoil to form a chromosome.

19 Review Essential Questions Which experiments led to the discovery of DNA as the genetic material? What is the basic structure of DNA? What is the basic structure of eukaryotic chromosomes? Vocabulary double helix nucleosome