AIM What is the structure of DNA?

DNA Deoxyribonucleic Acid The material that contains the information that determines inherited characteristics

Gene A segment of DNA that is located on a chromosome and codes for a specific trait Instructions for inherited traits Instructions for proteins

Searching for Genetic Material Fredrick Griffith: Discovery of Transformation – 1928 – 2 strains of bacteria (S causes pneumonia, R doesn’t) Transformation: A change in the genotype (genes) when cells take up foreign genetic material Outcome: Genetic Material can be transferred between cells

Searching for Genetic Material Oswald Avery: DNA is responsible for transformation – 1940’s – Wanted to see what caused transformation – 3 choices: DNA, RNA and Proteins – Used enzymes to destroy each part – Only when DNA was missing did transformation not occur Outcome: DNA is the transforming agent

Searching for Genetic Material Alfred Hershey and Martha Chase: DNA is hereditary material – 1952 – Studied bacteriophages (viruses that invade bacteria) Outcome: DNA is the hereditary material

The Shape of DNA James Watson and Francis Crick (February 28, 1953) Double Helix shape-strands of repeating subunits joined at the center

Nucleotides Subunit of DNA that consists of 3 parts Phosphate Deoxyribose Sugar Nitrogenous Base The information in DNA is contain in the order of the nitrogenous bases Base-pairing structure allows DNA to be copied quickly

Nitrogenous Bases Purines Two rings of Carbon per base Adenine Guanine Pyramidines One ring of Carbon per base Thymine Cytosine

Base-Pairing A purine is always paired with a pyramidine based on their chemical structure They are held together with weak Hydrogen bonds A always pairs with T C always pairs with G

Complementary Strands Now that we know the base-pairing rule we can construct complementary strands If given one strand (side) of the DNA, we can construct the other strand EX: TATGAGACT This ensures that each strand has the same information, with one side being the reverse of the other

Discovering the Structure of DNA Erwin Chargaff: 1949 – In every DNA the number of Adenine was equal to the number of Thymine and the number of Guanine was equal to the number of Cytosine

Discovering the Structure of DNA Rosalind Franklin: 1952 – Used X-ray diffraction to take pictures of the two forms of DNA – These photographs show that DNA as it is in nature has a tightly coiled helix made of two chains of nucleotides

Discovering the Structure of DNA James Watson and Francis Crick: 1953 – Built models to figure out the structure of DNA – Double Helix with phosphate and deoxyribose sugars on the outside and nitrogenous bases on the inside Watson, Crick and Wilkens were awarded the Nobel Prize in 1962 for their disocovery Franklin who had died of Cancer was not named in the award