History of DNA

How do genes work?How do genes determine the characteristics of an organism?

Are genes single molecules?Are genes made up of many molecules?

In the 1900’s biologists were trying to find these answers.

In order to understand genetics, biologists had to figure out the chemical structure of a gene.

(what are the parts & pieces?)

Friedrich Meischer – 1870’sFirst to isolate DNA

Frederick Griffith - 1928

-Studied two types of bacteria (smooth/rough)-cause of pneumonia (lung disease)

Type 2- (Rough looking)•Rough looking (non-encapsulated)•When injected harmless

Type 1- (smooth looking)•Smooth looking (encapsulated)•Disease causing•Killed mice

Experiment # 1Does the disease causing bacteria produce a poison?

Heat Killed

disease causingbacteria (smooth)

Mouse LivedInjected into the mouse

Summary: The mouse lived, this suggests that diseasecausing bacteria (smooth) does not release a chemical poison.

Heat Killed

disease causing (smooth) Bacteria

+live harmless

(rough) bacteria

Injected into the mouse

Experiment # 2

Summary: By themselves neither should of made the mice sick,however, many of the mice got pneumonia and died. The lungsof the mice were filled with the disease causing bacteria.

DEAD

These experiments showed that one strain of bacteria could be transformed into another type of bacteria.

Griffith’s Conclusion

Griffith hypothesized that when the live, harmless bacteria and heat killed bacteria were mixed, some factor was transferred from the heat killed cells

into the live harmless cells. This factor may contain“information” that could transform the harmless

bacteria.

This was the first evidence that DNA stores and transmits genetic information.

Oswald Avery - 1944

Oswald Avery led a group of scientists to furtherinvestigate the work of Griffith. They wanted find out whichmolecule in the heat killed bacteria was the most important

for transformation.

Summary:Discovered that DNA stores and transmits the

genetic information from one generation of organisms to the next generation.

(DNA)

Edwin Chargaff – 1947Studied DNA in various species

Nitrogen bases are proportionate within a speciesRatio of bases are various between species

•Adenine and Thymine were found in proportionate amounts•Cytosine and Guanine were found in proportionate amounts

Chargaff’s Rules

Alfred Hershey and Martha Chase -1952

Their experiments concluded that the genetic material of the bacteriphage was DNA and not protein.

Rosalind Franklin & Maurice WilkinsEarly 1950’s

X-ray diffraction showed•DNA fibers had a twisted pattern•Large groups of molecules in the fibers were spaced out in equal intervals

James Watson & Francis Crick - 1953

•Watson Crick Model•“Double Helix”•Determined the shape and structure•Adenine bonds with Thymine•Cytosine bonds with Guanine

The End