MOLECULAR BASIS OF INHERITANCE

DNA : Structure of Polynucleotide Chain

● DNA − Polymer of deoxyribonucleotides

● Nucleoside = Nitrogenous base + Pentose sugar (linked through N −

glycosidic bond )

Example − adenosine, deoxyadenosine, cytidine, etc.

● Nucleotide = Nucleoside + Phosphate group (linked through

phosphodiester bond )

● Many nucleotides link together through 3′ − 5′ phosphodiester bond

to form polynucleotide chain (as in DNA and RNA).

● In course of formation of polynucleotide chain, a phosphate moiety

remains free at 5′ end of ribose sugar (5′ end of polymer chain) and

one OH group remains free at 3′ end of ribose (3′ end of polymer

chain).

https://drive.google.com/file/d/1Mggnyxujr5r3tK69DBI6z6UTchdVsHk6/view?usp=sharing

Discovery of DNA as a Genetic Material

● Though principles of inheritance and discovery of chromosomes in

nucleus were achieved long time back, there was confusion about

which molecule acted as genetic material.

Transforming Principle

● Griffith performed experiments with the bacteria Streptococcus

pneumoniae . This bacterium has two strains − S strain and R strain.

S strain Bacteria                                     R strain Bacteria

○ Produce smooth colonies on          ○ Produce rough colonies onculture plate

culture plate                                       

○ Have a polysaccharide coat           ○ Do not have apolysaccharide coat

○ Virulent (causes pneumonia)     ○ Nonvirulent (does not cause pneumonia)

https://drive.google.com/file/d/1OJYTrl0qy884zFeuojt6QiJMzFBUxbwI/view?usp=sharing