DNA timeline

By Eloi Martinez
  • Mid-1800s – Friedrich Miescher

    Mid-1800s – Friedrich Miescher

    Experiment: Discovered nucleic acids while analyzing pus cells from surgical bandages. Summary: First to identify "nuclein" (later called DNA), showing that a new substance distinct from proteins existed in the cell nucleus.
  • Early 1900s – Phoebus Levene

    Early 1900s – Phoebus Levene

    Experiment: Identified the components of DNA (sugar, phosphate, and base) and defined the nucleotide. Summary: Correctly described nucleotides, but incorrectly proposed the "tetranucleotide hypothesis," thinking DNA was too simple to carry genetic information.
  • 1928 – Frederick Griffith

    1928 – Frederick Griffith

    Experiment: Transformation in Streptococcus pneumoniae. Summary: Showed that harmless bacteria (R strain) could be "transformed" into virulent ones when mixed with heat-killed deadly bacteria (S strain). Proposed the existence of a "transforming principle."
  • 1944 – Oswald Avery, Colin MacLeod & Maclyn McCarty

    1944 – Oswald Avery, Colin MacLeod & Maclyn McCarty

    Experiment: Enzyme treatment of Griffith’s experiment. Summary: Demonstrated that DNA (not protein) was the "transforming principle" by showing that DNase destroyed transformation, but protease did not.
  • Late 1940s–1950 – Erwin Chargaff

    Late 1940s–1950 – Erwin Chargaff

    Experiment: Base composition studies. Summary: Measured nucleobase ratios in many organisms and discovered that Adenine = Thymine, and Cytosine = Guanine. These findings became known as Chargaff’s Rules.
  • 1952 – Alfred Hershey & Martha Chase

    1952 – Alfred Hershey & Martha Chase

    Experiment: Blender experiment with bacteriophages labeled with radioactive sulfur (proteins) and phosphorus (DNA). Summary: Proved that DNA, not protein, enters bacteria during viral infection, confirming DNA is the genetic material.
  • 1953 – Rosalind Franklin, Maurice Wilkins, James Watson & Francis Crick

    1953 – Rosalind Franklin, Maurice Wilkins, James Watson & Francis Crick

    Experiment: X-ray crystallography and DNA modeling. Summary: Franklin’s famous Photo 51 revealed the helical structure of DNA. Watson Crick, using her data without proper credit, built the correct double helix model. Published in Nature (April 1953).