Website Search
ID 16374

Concept 17: A gene is made of DNA.

Concept 17:  A gene is made of DNA.
Oswald Avery's team proves that DNA, not protein, is the genetic molecule.
In the 1920s, experiments showed that a harmless strain of bacteria can become infectious when mixed with a virulent strain of bacteria that had been killed. The dead bacteria apparently provide some chemical that "transforms" the harmless bacteria to infectious ones. This so-called "transforming principle" appeared to be a gene. A team of scientists led by Oswald Avery at the Rockefeller Institute, rigorously followed up on these experiments in the 1940's. They found that a pure extract of the "transforming principle" was unaffected by treatment with protein-digesting enzymes but was destroyed by a DNA-digesting enzyme. This showed that the transforming principle is DNA — and, by extension, a gene is made of DNA. Still, many scientists were slow to accept this clear proof that DNA, not protein, is the genetic molecule.
oswald avery, protein digesting enzymes, strain of bacteria, harmless bacteria, genetic molecule, virulent strain, transforming principle, dna
Creative Commons License This work by Cold Spring Harbor Laboratory is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 United States License.

Related content:

15674. Oswald Avery (c.1930)
Oswald Avery, circa 1930.
15012. Oswald Avery
In 1944, Avery and MacLeod, and McCarty purified the transforming principle of Fred Griffith's earlier experiment with pneumocossus bacteria. By a process of elimination, these scientists showed that DNA was the factor that caused genetic transformation.
16375. Animation 17: A gene is made of DNA.
Oswald Avery explains Fred Griffith's and his own work with Pneumococcus bacteria.
16705. Animation 34: Genes can be moved between species.
Stanley Cohen and Herbert Boyer transform bacteria with a recombinant plasmid, and Doug Hanahan studies induced transformation.
16393. Problem 17: A gene is made of DNA.
Experiment with rough and smooth Pneumococcus DNA.
16395. Animation18: Bacteria and viruses have DNA too.
Joshua Lederberg worked with bacterial genetics while Alfred Hershey showed that DNA is responsible for the reproduction of new viruses in a cell.
16391. Biography 17: Oswald Theodore Avery (1877-1955)
In 1944, Oswald Avery and his colleagues, Colin MacLeod and Maclyn McCarty published their landmark paper on the transforming ability of DNA.
15476. Mechanism of Recombination, 3D animation with with basic narration
Genetic engineering: inserting new DNA into a plasmid vector.
16392. Biography 17: Maclyn McCarty (1911- 2005)
In 1944, Maclyn McCarty and his colleagues, Colin MacLeod and Oswald Avery published their landmark paper on the transforming ability of DNA.
16381. Gallery 17: Oswald Avery's letter to his brother, 1943
A page from the May 15, 1943 letter from Oswald Avery to his brother Roy. In the letter Avery speculated on how transformation could happen. Avery never publicly connected genes with DNA and his transformation experiments.
Cold Spring Harbor Laboratory
CSHL HomeAbout CSHLResearchEducationPublic EventsNewsstandPartner With UsGiving