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

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The discovery of DNA Double Helix is one of the
greatest findings of all time, but its also one
of the most controversial
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KEY SCIENTISTS INVOLVED
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Issues to Cover
What is DNA?
Scientific Thinking before 1953
Social and Cultural Background
Watson and Cricks Contribution
Franklins Contribution

• 2 Forms of DNA

• X-ray Crystallography

Paradigm Shift
DNA Applications
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What is DNA?
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DNA (Deoxyribonucleic Acid)
DNA is a double stranded molecule that is twisted
into a Helix (Spiraling Staircase)
DNA Double Helix
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Each strand consists of
1) A Sugar Phosphate Backbone
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Each strand consists of
1) A Sugar Phosphate Backbone
2) Four Base Chemicals (Attached in Pairs)
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Perkins Model
1. Long Search
The search for the secret of life dates back
nearly a century prior to Watson and Cricks
ground breaking discovery in 1953
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The Early Efforts
Gregor Mendel Introduces the concept of heredity
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The Early Efforts
Wilhelm Johannsen Coins the term Gene
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The Early Efforts
Thomas Hunt Morgan Discovers that genes are
responsible for inheritance
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The Early Efforts
Phoebus Levene Discovers that DNA is made up of
nucleotides, phosphates, sugars and 4 bases
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The Early Efforts
Oswald Avery Shows that DNA can transform the
property of cells
However, this idea was not universally accepted
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The Early Efforts
Erwin Chargaff Shows that A G T C 50
Chargaffs Rule is an important equation in the
discovery of the structure of DNA
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Background
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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.
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VS
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Kings College

• Rosalind Franklin accepts a job at Kings
  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

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Franklins Work
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TWO FORMS OF DNA
In 1951 Rosalind Franklin discovers the Two Forms
of DNA through her X-ray diffraction images.
A Dry Form
B Wet Form
Photo 51
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X-Ray Crystallography
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Watson and Cricks Work
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Watson and Cricks 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)
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Perkins Model
2. Little Apparent Progress
Watson Cricks early model of DNA showed that
the structure

• Was a Triple Helix

• Had the Bases on the Outside

• Had the Sugar Phosphate Backbone on the Inside

However, Franklin disproves their model.
This sends them back to the drawing board. Watson
and Cricks supervisor stops them from model
building.
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Social and Cultural Environment

• 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 Kings College
• She has no one to share ideas and collaborate
  with
• She is fed up and decides to leave Kings
  College
• But before she does, Franklin promises to finish
  writing up her research papers
• In the process of her move, Wilkins gets hold of
  Franklins work which contained the famous photo
  51

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Perkins Model
3. Precipitating Event
In 1951, Maurice Wilkins gives James Watson
Rosalind Franklins work
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Perkins Model
4. Cognitive Snap
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
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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
Photo 51
They used Chargaffs Rule to figure out how the 4
Bases match up in pairs
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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

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Nature
Watson Crick quickly published their Scientific
Journal called Nature on April 25th 1953
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The Nobel Prize

• In 1962 Watson, Crick Wilkins won the Nobel
  Prize for their
• discovery of the structure of DNA

• However, there is no mention of Franklins key
  work.

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Perkins Model
5. Transformation

• Paradigm Shift
• Prior to Watson and Cricks discovery it was
  believed that
• Proteins were responsible for heredity because
  of their complex structure
• DNA was too simple for heredity because it only
  contained 4 bases
• 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

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DNA Applications
Science and Technology have advanced
astronomically since the discovery in 1953 Here
are some of the achievements since that time

• Cloning
• Genetically Modified Foods
• Genetic Engineering
• DNA Fingerprinting/Analysis

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Thank You!