1869 – Johann Miescher Studied the nuclei of white blood cells Isolated the material using HCl (aq) and digestive proteins Named the substance nuclein Found the material was rich in nitrogen and phosphorus

1919 – Pheobus Levene Discovered that DNA was made up of chains of nucleotides ACID RIBOSE NITROGEN RICH

1920 – DNA vs Protein thought that 4 nucleotides were connected in the same repeated pattern protein have 20 amino acids which could be combined in many combinations RNADNA sugar location bases RNADNA sugarribosedeoxyribose (one less oxygen) location bases RNADNA sugarribosedeoxyribose (one less oxygen) locationmainly outside nucleusmainly inside nucleus bases RNADNA sugarribosedeoxyribose (one less oxygen) locationmainly outside nucleusmainly inside nucleus basesAGCUAGCT

Levene’s Nucleotide Pattern

1928 – Frederick Griffith studied two strains of pneumococcus bacteria rough strain = nonvirulent injection into mouse did not result in death smooth strain = virulent injection caused mouse to die ?v=vQOdDGM5vSg ?v=vQOdDGM5vSg

Griffith’s Experiment

Griffith’s Conclusions some “factor” from the dead, virulent smooth strain “transformed” the living, non-virulent rough strain non-virulent rough strain picked up DNA to become virulent

1930 – Joachim Hammerling nucleus at bottom of stalk Acetabularia – type of alga

Hammerling’s Experiment Hereditary information is stored in the nucleus. no regrowth

1944 – Avery, McCarty & MacLeod continued Griffith’s work with pneumococcus Condition TestedResult pneumococcus & protease pneumococcus & DNAse Condition TestedResult pneumococcus & protease non-virulent bacteria  virulent bacteria pneumococcus & DNAsenon-virulent bacteria remained non-virulent

1940s – Joshua Lederberg demonstrated bacterial conjugation bacteria can exchange DNA bacteria have no nucleus or chromosomes v=7stZk6TesKk v=7stZk6TesKk

1940s – Edwin Chargaff for all organisms A = T and G = C Chargaff’s Rule organisms with more Gs and Cs tend to be more complex

1952 – Hershey & Chase conducted experiments to definitively show that DNA is the hereditary material bacteriophage used to infect bacteria bacterial virus m/watch?v=3QJ4CjFsfl A m/watch?v=3QJ4CjFsfl A

1950s – Maurice Wilkins & Rosalind Franklin

X-ray Crystallography physics approach to examining biological molecules Start at 14:35

Rosalind Franklin’s X-rays The photo indicated: 1. Backbone of alternating phosphate and sugars 2. Backbone is a helical structure 3. Double helix structure (molecule is a uniform helix) 4. Nitrogenous bases are in the middle of the molecule 5. Bases are at right angles to the backbone

Base Pairing knew that each base could pair with itself

1953 – James Watson & Francis Crick inspired by alpha-helix model of proteins determined how A + T and G + C bonded together width of purine + pyrimidine bonds fit perfectly between the sugar-phosphate backbone the double helix model offered an easy method for replication