The discovery of DNA Double Helix is one of the greatest findings of all time, but it’s also one of the most controversial

KEY SCIENTISTS INVOLVED

Rosalind Franklin James WatsonFrancis CrickMaurice Wilkins

What is DNA?

DNA (Deoxyribonucleic Acid) DNA is a double stranded molecule that is twisted into a Helix (Spiraling Staircase) DNA Double Helix

Each strand consists of: 1) A Sugar Phosphate Backbone

Each strand consists of: 2) Four Base Chemicals (Attached in Pairs) 1) A Sugar Phosphate Backbone

1. Long Search: The search for the secret of life dates back nearly a century prior to Watson and Crick’s ground breaking discovery in

Gregor Mendel: Introduces the concept of heredity The Early Efforts

Wilhelm Johannsen: Coins the term “Gene” The Early Efforts

Thomas Hunt Morgan: Discovers that genes are responsible for inheritance The Early Efforts

Phoebus Levene: Discovers that DNA is made up of nucleotides, phosphates, sugars and 4 bases The Early Efforts

Oswald Avery: Shows that DNA can transform the property of cells The Early Efforts However, this idea was not universally accepted

Erwin Chargaff: Shows that: A + G = T + C = 50% The Early Efforts Chargaff’s Rule is an important equation in the discovery of the structure of DNA

Background

Soon after WWII the race to discover the “Secret of Life” was on. Scientists knew this would be the discovery of the century and would guarantee a Nobel Prize.

VS James Watson Francis Crick Cambridge University Rosalind Franklin Maurice Wilkins King’s College Caltech University Linus Pauling

King’s College Rosalind Franklin accepts a job at King’s College to work in Maurice Wilkins’ Lab At the time of her arrival Wilkins is away on other matters When Wilkins returns, he discovers that his lab is taken over by Franklin He notices that Franklin is very intelligent and is able to work independently She spends hundreds of hours perfecting her X-ray Diffraction images and hand written calculations Wilkins is still under the impression that Franklin is his assistant There is a lot of tension in the lab due to miscommunication and personality clashes FranklinWilkins King’s College

Franklin’s Work

In 1951 Rosalind Franklin discovers the Two Forms of DNA through her X-ray diffraction images. A – Dry FormB – Wet Form TWO FORMS OF DNA Photo 51

X-Ray Crystallography

Watson and Crick’s Work

In 1951 James Watson traveled from the United States to work with Francis Crick at Cambridge University Watson and Crick used the “Model Building” approach They physically built models out of wire, sheet metal, nuts and bolts to come up with the structure of DNA Why did they build models? “Sometimes the fingers can grasp what the mind cannot” (Biology the Science of Life) Watson and Crick’s Work

Watson & Crick’s early model of DNA showed that the structure: However, Franklin disproves their model. Was a Triple Helix Had the Bases on the Outside Had the Sugar Phosphate Backbone on the Inside This sends them back to the drawing board. Watson and Crick’s supervisor stops them from model building.

Science at the time was a male dominated field Women did not receive equal treatment Women were forbidden in the lunch room Franklin is unhappy at King’s College She has no one to share ideas and collaborate with She is fed up and decides to leave King’s College But before she does, Franklin promises to finish writing up her research papers In the process of her move, Wilkins gets hold of Franklin’s work which contained the famous photo 51 Social and Cultural Environment

In 1951, Maurice Wilkins gives James Watson Rosalind Franklin’s work

Watson: “The instant I saw the picture my mouth fell open and my pulse began to race.” Page 196: Rosalind Franklin The Dark Lady of DNA

How Watson and Crick Solved the DNA Structure They already knew from Franklin and Wilkins’ work that DNA was in the form of a Double Helix They used Chargaff’s Rule to figure out how the 4 Bases match up in pairs Photo 51

How Watson and Crick Solved the DNA Structure They discovered that: The Phosphate Backbone was on the outside Which protected the Bases on the inside DNA acts as a Template or a Copying Mechanism for reproduction

Watson & Crick quickly published their Scientific Journal called “Nature” on April 25 th 1953 “Nature”

In 1962 Watson, Crick & Wilkins won the Nobel Prize for their discovery of the structure of DNA The Nobel Prize However, there is no mention of Franklin’s key work.

Discovering the Structure of DNA enabled the Scientific Community to understand the “Secret of Life” and how all life on earth is passed down from generation to generation

DNA Applications Cloning Genetically Modified Foods Genetic Engineering DNA Fingerprinting/Analysis Science and Technology have advanced astronomically since the discovery in 1953 Here are some of the achievements since that time: