The document outlines the major discoveries in DNA research from 1910 to 1953. It begins with Thomas Morgan's confirmation in 1910 that chromosomes are the molecules of inheritance. Important early experiments were conducted by Griffith in 1928 and Avery in 1944 suggesting DNA was the molecule of inheritance. In 1950, Chargaff determined purine and pyrimidine amounts were equal in DNA strands. Franklin photographed DNA in 1952 providing evidence it was a double strand. Watson and Crick used this photo and Chargaff's rules to develop their 1953 double helix model of DNA's structure.

1. DNA TIMELINE

2. What is DNA?
DNA stands for Deoxyribo Nucleic Acid.
DNA carries all of the genetic information for an
organism.

3. 1910: Thomas Morgan,
through experiments with
fruit flies, confirms that
chromosomes are the
molecules of inheritance.

4. 1928: Frederick Griffith conducts the first genetic
experiments on mammals.
His experiments dealt with mice and the
pneumonia virus.
He used two forms: the S form (deadly) and the R
form (not deadly).
A transforming material passed from dead S
bacteria to live R bacteria, making them deadly.

5. 1944: Oswald Avery
becomes the first scientist
to suggest that DNA was
the molecule of
inheritance.
Before Avery, biologists
believed inheritance was
controlled by proteins.

6. 1950: Edwin Chargaff
determines that certain
purines and pyrimidines
occur in equal amounts in
a DNA strand.
This leads to Chargaff’s
Rules: the amount of A =
the amount of T, and the
amount of G = the amount
of C.
“For every A there is a T, for every G there is a C”

7. 1952: Rosalind Franklin
photographs a DNA
molecule using an X-ray
camera.
Her photograph provides
evidence that DNA is made
of more than a single
strand of nucleotides.

8. Franklin’s co-worker,
Maurice Wilkins, gives the
photograph to a pair of
scientists, James
Watson & Francis
Crick , who are trying to
determine the structure of
DNA.

9. 1953: Using Franklin’s
photo and Chargaff’s Rules,
Watson & Crick develop
a model of DNA.
The model consists of two
strands of nucleotides
bonded together in the
shape of a twisted ladder.
This shape is known as the
double helix.

10. DNA Structure is the same in all organisms.
DNA is a Nucleic Acid (one of the macromolecules
[polymers] we learned about during our Biochemistry
unit) made up of long chains of nucleotides.
Each nucleotide has three parts.
phosphate group
deoxyribose (sugar)
nitrogen-containing
base

11. DNA Structure

DNA consists of two
strands of nucleotides.
DNA looks like a twisted
ladder
The “backbone” of the
ladder is formed by bonds
between the...
 Sugars (Deoxyribose)
 Phosphates.
The “rungs” of the ladder
are formed by hydrogen
bonds between
nitrogenous bases.
Nucleotide
Sugarphosphate
backbone
Hydrogen
bonds

12. 1. Purines: larger bases.
There are two
purines.
A. Adenine (A)
B. Guanine (G)
2. Pyrimidines: smaller
bases. There are two
pyrimidines.
A. Cytosine (C)
B. Thymine (T)
A
G
C
Phosphate
T
Deoxyribose

14. DNA Structure
Each base pair consists
of one purine and one
pyrimidine.
Pairs are bonded by
HYDROGEN BONDS
Following Chargaff’s
Rules , for every
Adenine (A) there will
be a Thymine (T), and
for every Guanine (G)
there will be a Cytosine
(C).
Label your diagram to
match this!
Nucleotide
Sugarphosphate
backbone
Hydrogen
bonds