DeoxyriboNucleic Acid The Blueprint of Life

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

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

Phoebus Levene (1910s) 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, MacLeod and McCarty (1944) Hershey and Chase (1952)

Avery, MacLeod, McCarty 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, MacLeod + 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, MacLeod and McCarty

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 DNA is double stranded in a double helix Strands are held together by H-bonds between nitrogenous bases A-T 2 hydrogen bonds G-C 3 Hydrogen bonds Backbone is made up of alternating sugar and phosphate 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