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

  • ID: 16374
  • Source: DNALC.DNAFTB

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Oswald Avery, circa 1930.

  • ID: 15674
  • Source: DNAi

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Oswald Avery explains Fred Griffith's and his own work with Pneumococcus bacteria.

  • ID: 16375
  • Source: DNALC.DNAFTB

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  • ID: 16705
  • Source: DNALC.DNAFTB

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Experiment with rough and smooth Pneumococcus DNA.

  • ID: 16393
  • Source: DNALC.DNAFTB

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  • ID: 16395
  • Source: DNALC.DNAFTB

16391. Biography 17: Oswald Theodore Avery (1877-1955)

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  • ID: 16391
  • Source: DNAFTB

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Genetic engineering: inserting new DNA into a plasmid vector.

  • ID: 15476
  • Source: DNALC.DNAi

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.

  • ID: 16392
  • Source: DNAFTB

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.

  • ID: 16381
  • Source: DNAFTB