Why DNA is the substance of hereditary?: The Griffith Experiment --> transform one bacteria type into another if both are mixed together --> through a mysterious transformation process

Avery, Macleod & McCarthy Experiment: set out to discover tranforming factor involved --> separate all cell contents --> lipids (fats), proteins, RNA, carbohydrates (sugars) --> + clear stringy substances: the transforming factor --> discovered --> chemical tests show it is DNA (deoxyribose nucleic acid)

The Hershey-Chase experiment: DNA does not seem complex enough to be hereditary --> use E.Coli to show beyond question that DNA is the hereditary material --> infection by phage --> into bacteria --> phage: DNA + protein only --> which of these are injected for infection, hence hereditary --> DNA: phosphorus & protein: sulfur --> both are radioactive --> Hot DNA & Hot protein --> phage re-produces --> the offspring phages only has Hot DNA --> conclusion: DNA is the hereditary material

P.A. Levene 1920s: found the composition of DNA --> phosphate + deoxyribose sugar + bases --> nucleotide: P + sugar + 1 base (A,C,T,G)

DNA structure: how DNA looks like --> Watson-Crick DNA model --> helix structure --> 2 parallel P-sugar strands --> they are then twisted together into the double helix --> steps: A-T & C-G --> nos. A = nos. T & nos. C = nos. G

Replication: unwinds --> each strand (parent) replicates the daughter strand (almost exact copy) --> semi-conservative replication --> replication occur at multiple different points along the DNA