The genetic material

DNA

Sayma Zerin 1st year,B.S.(Hons.) Dept. of Genetic Engineering & Biotechnology

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?

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

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.

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 notprove the statement

Discovery of Transformation in Bacteria:In 1928, Frederick Griffith 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

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.

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”

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.

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.

The End