DNA, not protein, is the genetic material. This is demonstrated through three classic experiments:
1) Frederick Griffith's 1928 experiment on bacterial transformation showed that a "transforming principle" in heat-killed bacteria could cause non-virulent bacteria to become virulent.
2) The 1944 experiment by Avery, MacLeod, and McCarty identified DNA as the transforming material in Griffith's experiment.
3) The 1952 experiment by Hershey and Chase, using bacteriophage, provided evidence that viral DNA, not protein, enters the host bacteria to cause new phage production.
2. GENETIC MATERIAL MUST BE
CAPABLE OF-
• Replication
• Storage of information for expression of traits
• Control expression of traits
• Change in controlled way
• Must be stable
3. IS THE GENETIC MATERIAL PROTEIN OR DNA?
DNA PROTEIN
DNA molecule is packaged into chromosomes Chromosomes are also known to contain protein
Only four different subunits make up DNA 20 different subunits – greater potential variety of
combinations
Chromosomes contain less DNA than protein by
weight
Chromosomes contain more protein than DNA by
weight
• Classical experimental data confirmed DNA as the genetic material.
• Earlier it was a challenge to demonstrate that DNA was indeed the molecule that contained genetic information
4. EXPERIMENTS-
On the basis of certain experiments conducted from time to time it was ultimately
demonstrated that DNA carries genetic information and not the proteins, that
experiments are-
1. Frederick Griffith’s Experiment (1928) on Bacterial Transformation
2. Oswald Avery, Colin MacLeod and Maclyn McCarty’s Experiment (1944) on
transformation
3. Alfred Hershey and Martha Chase Experiment (1952) on T-2 Bacteriophage
5. GRIFFITH TRANSFORMATION
EXPERIMENT(1928)
• Experiments with smooth (S), virulent strain Streptococcus pneumoniae, and rough (R),
nonvirulent strain
• Bacterial transformation demonstrates transfer of genetic material
• The ability of a substance to change the genetic characteristics of an organism is
known as transformation.
• Griffith concluded that the R-strain bacteria must have taken up what he called a
"transforming principle" from the heat-killed S bacteria, which allowed them to
"transform" into smooth-coated bacteria and become virulent
7. AVERY-MACLEOD-MCCARTY
EXPERIMENT (1944)
• Set out the experiment to identify Griffith's "transforming
principle."
• Determined that DNA is the transformation material
• DNA is the agent transforming the R strain into virulence.
• If the DNA in an extract of heat-killed S-strain cells is destroyed,
then mice survive when injected with a mixture of the heat-killed
cells and the live nonvirulent R-strain cells.
9. HERSHEY AND CHASE
EXPERIMENT(1952)
• Alfred Hershey and Martha Chase provide convincing evidence that DNA is genetic
material
• Using bacteriophage, a type of virus that have a very simple structure an outer core and an
inner component
• The phage are made up of equal parts of protein and DNA.
• Use radioactive labels 32P for DNA and 35S for protein
• Interested in finding out whether it was the protein component or the DNA component
that got deposited inside the infected cell.
• They determined that the DNA was indeed introduced into the infected bacteria, causing
proliferation of new phage.
10. HERSHEY AND CHASE EXPERIMENT
https://simple.wikipedia.org/wiki/Hershey%E2%80%93Chase_experiment
