Drill “All living things have me in them. Some people call me the ‘code of life.’ I was discovered in 1874. The amount of me in a person’s body could stretch 13.5 times to the Sun. In a chimpanzee, I am 98.5% similar to that of a human. Who am I?”

DNA: The Genetic Material Section 12.1 Discovery of the Genetic Material April 6, 2009

The Miraculous Acid In 1874, Friedrich Miescher discovered acid molecules in the nuclei of pus cells. This acid became known as deoxyribonucleic acid or DNA.

What is the genetic material? Frederick Griffith – British microbiologist In 1928, first to show that bacteria are capable of transferring genetic information. This became known as the “transforming principle.”

Griffith’s Experiment Used two strains of Pneumococcus bacteria: S – strain has mucus coating. will cause fatal pneumonia in mice. R – strain has no coating. does not harm mice. S strain R- strain

Griffith’s Experiment

Griffith’s Conclusion What? You want me to just tell you… Griffith did not know that the “transforming principle” was DNA. Today we know that bacterial cells have small circular molecules of DNA called plasmids that can be passed between bacteria.

Oswald Avery Canadian physician and bacteriologist In 1944, with coworkers, McCarty & MacLeod, he discovered that the “transforming principle” was DNA. Very cautious to report his findings.

Avery, McCarty, & MacLeod, 1944 Repeated Griffith’s experiments with R- and S-strain Pneumococcus bacteria. Purified extracts of S-strain bacteria. Treated extracts with protease – an enzyme that destroys proteins Bacteria still transform. Treated extracts with deoxyribonuclease – an enzyme that eliminates DNA No transformation.

Alfred Hershey & Martha Chase American geneticists In 1952, identified DNA to be the genetic material of phages – small viruses that infect bacteria -- and ultimately, all organisms.

The Blender Experiment

Section 12.1 Big Ideas It took almost 80 years between the discovery of DNA and scientist’s understanding of its significance. Significant scientific discovery results from the application of the scientific method.

Section 12.1 Big Ideas Science is often advanced by the careful repetition, with modification, of the experiments of others. DNA is the genetic material of all living organisms.

References: www.blc.arizona.edu/ INTERACTIVE/DNA3/DNA1.html http://www.pbs.org/wgbh/nova/photo51/before.html www.bio.davidson.edu/.../ Publicschedule.html http://library.thinkquest.org/20465 http://www2.carthage.edu/~pfaffle/hgp/PF.html http://en.wikipedia.org/wiki/Transforming_principle