* Gregor Mendel had no experience with DNA – did pea pod experiment * Proteins at one point were considered as the genetic material * Miescher: found a phosphorus rich substance in puss cells * Levene: isolated 2 types of nucleic acids * Hammerling: worked with acetabularia. (Reciprocal graft experiment) * Griffith: wanted to make a vaccine. * Worked with Live S strain and R strain. * A chemical substance from one cell is capable of genetically transforming another cell * Conjugation (transforming principle) * Avery, MacLeod and McCarty extended Griffiths experiment. * Used RNase, Proteases and DNase. * According to Chargaff’s rule: A=T and C=G * Hershey and Chase: worked with the bacteriophages * Tagged on batch in a radioisotope of Sulfur and one in Phosphorus * Mixed bacteriophages with bacteria (bacterial cells are infected) * Agitate to remove phages from bacterial cells * Centrifuge: so that the bacterial cells form pellets * Is the radioactivity in the pellet, or the liquid? Ta da.

* DNA: characteristics in species, variation, control cellular processes and replication. * Rosalind Franklin: helical structure, 2 nm in diameter, bases are hydrophobic, sugar phosphate backbones are hydrophilic * Antiparallel, 5’ – 3’, complementary base pairing * 2 Challenges of RNA: must be compact to prevent interference with other cellular processes and must be protected from hydrolytic enzymes * In prokaryotes, genetic material is in a double stranded single DNA. It undergoes supercoiling. * Organization of genetic material in eukaryotes: * 8 histones are wrapped by DNA and locked by H1 histone forming a nucleosome * Nucleosomes line up making a solenoid structure * The log chain of nucleosomes loop in on each other and attach to a protein scaffold * Then the protein scaffold loops in on itself making a chromosome

DNA REPLICATION

* 3 models: Semi-conservative, conservative and dispersive * Process of DNA replication: Initiation, Elongation and Termination * DNA gyrase: swivels to release tension. (Cutting and gluing) * DNA helicase: unwinds and unzips * SSB proteins: allows the strands to stay separated * DNA polymerase III: works after RNA primase and synthesizes in the 5’ to 3’ direction. * RNA primase: lays down primer which is the start point of DNA replication * Prevention of losing genes: we have telomeres (buffers) * Erosion of telomeres = cell death * DNA polymerases act as