Molecular interaction, found in the structure of DNA-

Ans. is 'd' i.e., All of the aboveo Bonds involved in DNA structure are -i) With in nucleotides : Glycosidic bond between carbon-1 of pentose sugar (deoxyribose) and nitrogen-9 of purine base or nitrogen-1 of pyrimidine base.ii) Between two strands of DNA ; The two chains (strands) are held together by hydrogen bonds between complementary pairs of bases. Adenine is always paired with thymine by formation of two hydrogen bonds and Guanine is always paired with cytosine by formation of three hydrogen bonds.Between suecesive nucleotides : Successive nucleotides in a strand of DNA are attached to each other by 51-31 phosphodiester bonds. Carbon-31 and -51 of deoxyribose subunits are involved in ester linkages with an inorganic phosphate to form a 31, 51 phosphodiester bond (a covalent bond). Thus alternating phosphate and deoxy ribose units form the backbone structure of DNA while purine and pyrimidine bases are stacked inside.Base-staking interactions : The bases (purines and pyrimidines) lie flat in the interior, stacked on top of one another. They interact with one another through vander waals forces and hydrophobic interactions. Collectively these two are known as base-stacking interactions.