Deoxyribo Nucleic Acid The Blueprint of Life Who

Deoxyribo. Nucleic Acid The Blueprint of Life

Who discovered DNA? • Swiss chemist Friedrich Miester in 1869 • Nobody cared

Assumption of the Time • Proteins were wellknown and assumed to be the genetic carrier • Lots of different proteins discovered, 20 different amino acids

Phoebus Levene (1910 s) • Russian biochemist who studied DNA, or nuclein as it was originally called • Discovered structure of nucleotides and • the presence of 4 unique DNA nucleotides

Nucleotide Structure

How Did We Determine DNA was the Genetic Material? • Two major sets of experiments conducted over 20 -30 years • Avery, Mac. Leod and Mc. Carty (1944) • Hershey and Chase (1952)

Avery, Mac. Leod, Mc. Carty • Tried to explain the findings of Frederick Griffith in 1928

Griffith’s Experiment • Passage of a substance could transform harmless bacteria into deadly virulent bacteria

Avery, Mac. Leod + Griffith • Demonstrated that transformation occurred when proteins were removed • Transformations did not occur when DNA was removed • Thus it was the DNA responsible for transforming a bacteria

Avery, Mac. Leod and Mc. Carty

Alfred Hershey and Martha Chase • Tried to explain how bacteriophages invaded bacteria and changed their behavior • It was known that bacteriophages consisted of proteins and DNA

Results of Hershey Chase

Erwin Chargaff • Species differed in the number of each nucleotide they contained • The number of As and Ts was usually similar, same with Gs and Cs

Rosalind Franklin and Maurice Wilkins • Used a technique called X-Ray Crystallography to study shape

The X-Ray Image • Demonstrated that the shape of DNA was a double helix, with the nitrogenous bases on the inside • She independently discovered the structure of DNA

They Did Her Dirty • Her X-Ray image was shown to other scientists (including Watson and Crick) without her permission • Watson and Crick used the X-Ray and some of Franklin’s earlier work to suggest the double helix model of DNA • She died at 37 so we’ll never know if she would have shared in their Nobel Prize

James Watson and Francis Crick

Watson and Crick • Published their model in a 1 page paper • Literally had made models out of cardboard until one fit

Key Points in the Model 1. DNA is double stranded in a double helix 2. Strands are held together by H-bonds between nitrogenous bases 1. A-T 2 hydrogen bonds 2. G-C 3 Hydrogen bonds 3. Backbone is made up of alternating sugar and phosphate 4. DNA strands are anti-parallel (run in opposite directions)

DNA Model • Working in groups you will design and build a simple model of DNA • It should demonstrate the 4 key points of the Watson/Crick model • Can be made out of anything. Should have something representing Phosphate, Sugar, each of the 4 bases and H-bonds (the correct number) • Due Monday