Biochemical Evidence For dna As Genetic Material What is genetic material The genetic information in all cell is stored in DNA ,Discovery of Transformation in Bacteria , The transforming principle is DNA , HERSHEY & CHASE (1952) EXPERIMENT WITH T2 BACTERIOPHAGE, Summary of Hershey & Chase (1952 ) experiment

1. PADMASHREE INSTITUTE OF
MANEGMENT AND SCIENCE.
Seminar topic on;
• Biochemical Evidence For dna As Genetic
Material
Presented by;
Shylesh murthy I .A
1st yr Msc
biotechnology
PIMS

2. The genetic material of
a cell or an organism
refers to those materials
found in the nucleus,
mitochondria and
cytoplasm, which play a
fundamental role in
determining the structure
and nature of cell
substances, and capable
of self-propagating and
variation.
What is genetic material?

3. Continue…
DNAProtein
RNA
Protein,RNA and
DNA were thought
as genetic material.
But many
experiments suggest
DNA as genetic
material rather than
protein and RNA

4. What is DNA?
•DNA contains three main components (1) phosphate (PO4)
groups;(2) five-carbon sugars; and (3) nitrogen-containing bases
called purines (adenine,A,and guanine,G) and pyrimidines(thymine,T,
and cytosine,C).nitrogen base and sugar make a nucleoside.
Phosphate group and a nucleoside make a nucleotide.
•DNA is composed of two strand of nucleotides. The two strands are
held together by H-bonds. (complementary base pairing)
•A pyrimidine in one chain is always paired with a purine in the other
chain
•DNA is deoxyribo nucleic acid. A German chemist,Friedrich
Miescher, discovered DNA in 1869.

5. The genetic information in all cell is stored in DNA
 Stability of DNA
 Location of DNA
 The constant molecular composition of DNA.
 A relation between the DNA & chromosomes.
These are strong evidence for the statement but these do not
prove the statement

6. Discovery of Transformation in Bacteria:
In 1928, discovered bacterial transformation.
He worked on Streptococcus pneumonieae (Pneumococcus)
Pneumococci have various strains which can be classified by-
1. The presence or absence of a polysaccharide capsule.
2. The molecular composition of the capsule.
When grown on blood agar medium, pneumococci with capsules are
virulent and form large, smooth colonies and designated as type S

7. s pneumococci mutate to an avirulent form that has no
capsules.
When grown on blood agar medium, these noncapsulated
pnuemococci form small, rough-surfaced colonies and designated
as type R
Based on the molecular composition of the capsule, these
pneumococci cells are type I, II, III, and so forth.

9. The transforming principle is DNA:
In 1944, Oswald Avery,Colin Mcleod & Maclyn McCarty proved
that the transforming material in pneumococci was DNA rather
than RNA or Protein
They concluded that “a nucleic acid of the deoxyribose type is the
fundamental unit of the transforming principle of Pneumococcus”

10. Genetic information is transmitted by DNA only
• The final evidence that DNA transmits genetic information was
provided by Hershey and Chase in 1952
• They experimented with T2 bacteriophages, viruses that attack
bacteria.

11. HERSHEY & CHASE (1952) EXPERIMENT WITH T2
BACTERIOPHAGE
In culture I Bacteriophage was grown in medium containing Radioactive
Phosphorus (32P))To make DNA Radioactive
In culture II Bacteriophage was grown in medium containing radioactive
Sulphur (35S) To make proteins Radioactive
Both kinds of Bacteriophage particles were allowed to infect Bacteria
The infected bacteria were observed for radioactivity
Radioactive Phosphorus was found with bacterial cells
Radioactive Sulphur was not traced in bacterial cells ( Only in Ghosts)
Bacteriophage progeny carried only radioactive phosphorus and not
radioactive sulphur

12. HERSHAY & CHASE CONCLUSION
As ghosts or coat of Bacteriophage were not labelled with 32P
and only with 35S. The results of experiment clearly indicate that
only DNA and not the proteins enter the bacterial cell. Protein coat
is left outside. The DNA entering the host cell carries all the genetic
information for synthesis of new phage particle. This certainly
proves that DNA is the genetic material in Bacteriophage and not
proteins

13. - Bacteriophage DNA was labeled with radioactive
phosphorus (32P)
- Bacteriophage protein was labeled with radioactive sulphur
(35S)
- Radioactive molecules were tracked
- only the bacteriophage DNA (as indicated by the 32P)
entered the bacteria and was used to produce more
bacteriophage
Conclusion: DNA is the genetic material
Summary of Hershey & Chase (1952 )
experiment

14. The End

15. References ; Biology
1. DR SUDAKAR RAO
2. V-k AGARWAL
3. Molecular biology by; George M, Malacinski