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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​
5
′
p
● Many nucleotides link together through 3′ ​ ​ ​hosphodiester 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).

Double Helix Model for the Structure of DNA

● Scientists involved

○ Friedrich Meischer​− First identified DNA as an acidic
substance present in nucleus and named it as ‘Nuclein’

○ Wilkins and Franklin​− Produced X­ray diffraction data for
DNA structure

○ Watson and Crick​− Proposed double helix structure model for

DNA based on X­ray diffraction data

○ Erwin Chargaff​− Proposed that in ds DNA, ratios A:T and C:G
remain same and are equal to one

Features of double helix structure of DNA: