Identifying Substances of Genes Chapter 12: DNA Identifying Substances of Genes

Bacterial Transformation Frederick Griffith (1879-1941) British Scientist Wanted to know what genes were made up of Focused on Bacteria Pneumonia found in mice 2 strands: (S strain was deadly; R strand was harmless) Ran a number of tests resulting in either live or dead mice Surprised that a mixture of heat killed S strain and live R strain killed mouse Gave him the idea of Transformation

Bacterial Transformation What is Transformation? Process of a gene changing the structure of bacteria from one strand to another Oswald Avery (1877-1955) American Conducts experiment in 1944 Ran the bacteria against all types of substances Transformation occurred However, when they ran an experiment to destroy the DNA, transformation did not occur

Bacterial Viruses Alfred Hershey and Martha Chase Wanted to determine if DNA or protein was genetic code Used a bacteriophage to run the experiment 1952: Which part of virus entered the cell? DNA or protein coat? Understood that one of the them entered into the cell Radioactive tags given to both protein and DNA After separation, they found that DNA was molecule of heredity

Role of DNA Storing Information Copying Information Controls blood type, eye color, and patterns of development Copying Information Needed for process of cell division Transmitting Information Used for when info is passed from parent to offspring

Chapter 12: DNA Structure of DNA

Components of DNA Nucleic Acids Nucleotides Molecules found in the cell’s nucleus Nucleotides Structure of DNA Consists of: Nitrogen base (Adenine, Thymine, Guanine, Cytosine) 5 carbon sugar (Deoxyribose) Phosphate group Covalent bonds are created between the sugar and phosphate group

Solving the Structure Chargaff’s Rule Erwin Chargaff (1905-2002) Austrian looking to figure out how DNA was structured Noticed proportions of nitrogen bases were similar Adenine appeared 29.3% Cytosine appeared 20% Guanine appeared 20.7% Thymine appeared 30% Adenine always goes with Thymine Cytosine always goes with Guanine All DNA has this

Solving the Structure Rosalind Franklin (1920-1958) Used x-ray defraction to help piece together part of structure X-rays hit a crystal in the middle of the space Causes light to shoot around object giving its shape Showed that DNA strands twisted around each other (helix) Showed it was made up of 2 strands Franklin would ultimately die at age 37 due to overexposure to radiation from x-rays

Solving the Structure James Watson and Francis Crick Watson (1928-) and Crick (1916-2004) Came up with the idea of the double helix structure Anti-parallel strands Twist around each other in opposite directions Bonds form between Adenine and Thymine; Cytosine and Guanine Everything held together by hydrogen bonds Durable enough to hold together but weak enough to allow flexibility and the strands to break apart during reproduction

Double Helix