Charles Darwin proposes that all life is deeply related and that there must be some underlying source of variation that is associated with how information is stored and passed on from one generation to the next.
Gregor Mendel investigates inheritance in pea plants, which leads to the idea that information needed to build an organism is packaged into a gene – some abstract kind of units associated with specific traits, segregated and sorted in reproduction
1920s: Based on groundwork laid by Max Planck in 1900 and Albert Einstein in 1905, a large group of physicists begin to develop Quantum Mechanics.
1932: Niels Bohr speaks to a group of clinicians in Copenhagen, Denmark, about the limits of investigating structure and function of living organisms at the subcellular level; he speculates that such study could kill the cell.
1935: Max DelbrĆ¼ck publishes āOn the nature of gene mutation and gene structure,ā in which he proposes that genes are likely to be large molecules. In 1937 he moves to the United States and begins working with bacteria and viruses (called ābacteriophagesā) as a way to investigate the physical properties of heredity.
Viruses are simple–consisting of protein, nucleic acid, and lipid–yet carry genes to replicate themselves
1944:
Erwin Schrƶdinger publishes What Is Life?, dealing with deep questions concerning the molecular basis of life and drawing attention to DelbrĆ¼ckās idea that genes are likely to be large molecules. His book inspires a signiļ¬cant number of physicists to research the physical basis of life, a ļ¬eld of study that eventually becomes called molecular biology.
Oswald Avery and colleagues publish a report that describes experiments with pneumococcal bacteria demonstrating that DNA can carry genetic information from one cell to another. The report concludes āa nucleic acid of the deoxyribose type is the fundamental unit of the transforming principleā (not protein). His work was essentially ignored by the scientiļ¬c community, which considered DNA too āstupidā a molecule to carry genetic information.
1952: Alfred Hershey and Martha Chase infect bacteria with T2 phages containing radioactive sulfur atoms (incorporated into protein) and radioactive phosphorous atoms (incorporated into DNA) and showed that it is the radioactive DNA that is transferred to the bacteria during viral infection (more below)
1953: Francis Crick and James Watson propose their famous double-helical structure for the DNA molecule.
Realized that genes where sequences of (A,T,C,G)s in DNA and that there was some genetic code between this DNA sequence and the ammino acids in proteins
Sought to answer the question: Are Genes Made of Protein or DNA?
Steps involved:
Bacteriophage virus T2 is grown on two different media: one containing radioactive sulfur atoms and one containing radioactive phosphorus atoms.
Most proteins contain sulfur atoms, while DNA does not; DNA contains phosphorus atoms, while proteins do not.
The viruses are allowed to infect bacteria in a solution with it’s genes, but not given enough time to replicate.
The cells are agitated (bended) enough to dislodge the virus particles from the surface of the bacteria.
Spinning in a centrifuge causes the larger, heavier bacteria to settle into a pellet at the bottom of the tube, while the smaller, lighter virus particles remain in the supernatant liquid.
Radioactivity remains in the supernatant, and thus protein stays with the original phages after the infection.
Radioactivity is in the pellet, and thus DNA is transferred to the bacteria during the infection; thus, Genes are made of DNA.
