Question

Glycosidic bonds exist in DNA molecule between
A. sugar and phosphate
B. any two nitrogen bases.
C. sugar and nitrogen base.
D. purines and pyrimidines.

Answer 1

Hint: DNA has all these molecules in it i.e. sugar, phosphate, nitrogenous base. Purines and pyrimidines are the nitrogenous bases. Through hydrogen linkage, purines get paired with pyrimidines.

Complete step by step solution:
Nucleic acids are classified as DNA and RNA
DeoxyRiboNucleic Acid, abbreviated as DNA, is a helical structure where two polynucleotide chains coil around each other and form a double helix. It is the carrier of genetic instructions. Ribonucleic Acid abbreviated as RNA is a biological molecule which serves in several biological roles. The key point that differs DNA from RNA is that DNA is double stranded and RNA is single stranded. RNA contains ribose while DNA contains deoxyribose.
DNA strands are made of small monomeric units called nucleotides and each nucleotide has nitrogen containing bases, sugar and phosphate. The nitrogenous bases are adenine, thymine, cytosine, guanine.
Nucleotide-nucleotide linkage - phosphodiester linkage
DNA is double stranded because four nitrogenous bases are paired with each other.
Adenine-Thymine
Cytosine-Guanine
The strands of DNA contain genetic information.
Glycosidic bond is a covalent bond that binds from a sugar molecule to any other molecule through –OH groups. It may or may not be a sugar molecule. It is usually unstable and have tendency to hydrolysis
${\text{A}} - {\text{OH}} + {\text{B}} - {\text{OH}} \to {\text{A}} - {\text{O}} - {\text{B}} + {{\text{H}}_2}{\text{O}}$
In DNA, it is between sugar and base. There is a phosphate between each sugar. So it is called phosphor diester linkage.
Additional information:
There are four types of glycosidic linkages-
O-glycosides – via oxygen
S-Glycosides – via sulfur
C-Glycosides – via carbon
N-Glycosides – via nitrogen

Note: Nitrogenous bases are of four types. The glycosidic bond is linked from sugar with any of the four nitrogenous bases using enzyme glycosylases. This can occur in either DNA or RNA. It is a type of covalent linkage i.e. electrons are shared between the atoms.