The Hunt for Fame Fortune and DNA

Chapter 13.1

AP BiologyFall 2010

Early and Puzzling CluesJohann Miescher is credited with the

discovery of DNA in the late 1800’s

Early and Puzzling CluesIn 1928, Fred Griffith was working with S

(pathogenic) and R (nonpathogenic) strains of a pneumonia-causing bacteriumInjected mice with R cells; mice livedInjected mice with S cells; mice died

Blood samples contained many live S cellsS cells were heat-killed, then injected into

mice; mice livedLive R cells plus heat killed S cells were

injected into mice; mice diedLive S cells were found in blood

Griffith Experiments

Early and Puzzling CluesSome substance from the S cells had

transformed the R cellsBoth proteins and nucleic acids were

candidates In 1944, Oswald Avery showed the substance

was DNA

Avery Experiments

Confirmation of DNA FunctionViruses called bacteriophages use bacterial

cells for reproduction Because they consist of only a protein coat

and a nucleic acid core, these viruses were used in experiments by Hershey and Chase to prove which of these was the heredity material It was the nucleic acid

Confirmation of DNA Function35S labeled proteins in the bacteriophage

coat did not enter the bacteria and thus were not participating in providing directions for new virus assembly

32P labeled DNA in the viral core did not enter the bacteria and directed new virus assembly

Confirmation of DNA FunctionLinus Pauling deduced the structure and

secrets of the protein collagen, bringing the biology community one step closer to DNA structural details

Enter Watson and CrickWatson and Crick used numerous sources

of data to build various models of DNAIn 1953, they discovered and published the

structure of DNA