Notes

•Frederick Griffith
-British bacteriologist whose 1928
experiment with bacterium was
the first to reveal the
“transforming principle”
which led to the discovery that
DNA acts as the carrier of
genetic information

experiments:
1.Avery’s DNA Experiment
• In a very simple experiment,
Oswald Avery's group showed
that DNA was the
"transforming principle."
When isolated from one strain
of bacteria, DNA was able to
transform another strain and
confer characteristics onto that
second strain. DNA was
carrying hereditary information.

2.Hershey- chase blender experiment
•The most well-known Hershey-Chase
experiment was the final experiment,
also called the Waring Blender
experiment, through which Hershey and
Chase showed that phages only injected
their DNA into host bacteria, and that the
DNA served as the replicating genetic
element of phages

3.Levene’s Nucleotides
• P. A Levene an American biochemist analyzed
the component of DNA.
• DNA composed of four nitrogenous bases
(cytosine, guanine, adenine and thymine)
deoxyribose sugar and a phosphate group.
•Building block of DNA as a NUCLEOTIDE
which base attached to sugar and phosphate
molecule.

4.Chargaff Rule
•Erwin Chargaff a Austrian biochemist
•He analyzed the proportion of the
nitrogenous bases in the DNA of various
species.
•Each species had unique percentages of
each type of nucleotide.
•DNA contains A, T, G and C which vary
from species to species.
•Within the species, the amount of base
pairs are equal that is A= T and G=C
• A – adenine = T – thymine
• G – guanine = C= cytosine

5.Rosalind Franklin’s X-ray Diffraction
• Studied the structure of DNA using a technique
known as X-ray crystallography.
• She delivered a lecture to a group of scientist
including James Watsons on the two forms of
DNA.
•Type A dry form
•Type B wet form

6.Watson and Crick DNA model
• Double helix resembles a
twisted ladder. Each 'upright'
pole of the ladder is formed
from a backbone of alternating
sugar and phosphate groups.
• Two strands connected by
hydrogen bonds. A bases are
always paired with Ts, and Cs
are always paired with Gs,
which is consistent with and
accounts for Chargaff's rule.