important people in bio

Frederick Griffith

Conducted the 1928 bacterial transformation experiment with Streptococcus pneumoniae in mice, discovering that a substance from heat-killed pathogenic bacteria could transform non-pathogenic bacteria into a virulent form.

Avery, MacLeod, and McCarty

Isolated cellular fractions from heat-killed bacteria in 1944 using specific enzymes, demonstrating that only the destruction of DNA with deoxyribonuclease prevented transformation, thus identifying DNA as the transforming principle.

Alfred Hershey and Martha Chase

Conducted the 1952 'blender experiment' using T2 bacteriophages labeled with radioactive phosphorus ($^{32}P$) for DNA and sulfur ($^{35}S$) for protein, confirming that DNA is the genetic material injected into bacterial host cells.

Erwin Chargaff

Analyzed base compositions of DNA across various species, establishing that the amount of adenine equals thymine ($\%A = \%T$) and guanine equals cytosine ($\%G = \%C$), known as Chargaff's rules.

Rosalind Franklin

Captured high-resolution X-ray diffraction patterns of crystallized DNA fibers, particularly 'Photo 51,' which provided crucial measurements demonstrating the helical structure, dimensions, and density of DNA.

James Watson and Francis Crick

Synthesized existing structural data and chemical rules in 1953 to construct the double-helix model of DNA, featuring antiparallel sugar-phosphate backbones and complementary internal nitrogenous base pairing.

Matthew Meselson and Franklin Stahl

Used density-gradient centrifugation with heavy ($^{15}N$) and light ($^{14}N$) nitrogen isotopes in 1958 to show that DNA replicates in a semi-conservative manner, where each daughter molecule retains one parental strand.