2. What is genetic material?
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 selfpropagating and
variation.
3. Continue…
RNA
Protein,RNA and
DNA were thought
as genetic material.
But many
experiments suggest
DNA as genetic
material rather than
protein and RNA
Protein
DNA
4. What is DNA?
•DNA is deoxyribo nucleic acid. A German chemist,Friedrich
Miescher, discovered DNA in 1869.
•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
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 by1. 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.
8.
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. Proof tha DNA is the genetic material in Bacteriophage T2
From this experiment it was proved that DNA is the genetic material that
transfer hereditary information.
