Question

Read (i) to (v) and find the correct option.
(i) Nitrogen base is linked to pentose sugar through $N-$glycosidic linkage
(ii) Phosphate group is linked to $5^{\prime }-OH$ of a nucleoside through phosphoester linkage
(iii) Two nucleosides are linked through $3^{\prime }-5^{\prime }N-$glycosidic linkage
(iv) Negatively charged $DNA$ is wrapped around positively charged histone octamer to form nucleosome
(v) Chromatin that is more densely packed and stains dark is called euchromatin

• A. i and ii are wrong
• B. iv alone is wrong
• C. iii and v are wrong
• D. i alone is wrong

Answer 1

The correct option is C iii and v are wrong

Two nucleosides are linked through $1-4$ glycosidic linkage where the bond is normally formed between the carbon $1$ of one sugar and carbon $4$ of other sugar. Chromatin is a substance of which eukaryotic chromosomes are composed. It consists of proteins (principally histones), $DNA$ and small amounts of $RNA$. The $DNA$ molecule is wrapped around the histones to form a series of linked globular nucleosomes, resembling beads on a string. This itself is coiled to form a highly condensed solenoid arrangement, constituting a form of chromatin called heterochromatin, which stains densely with basic stains. The genes in the solenoid can only be transcribed if the solenoid unfolds to some extent, forming an expanded chromatin (euchromatin), which is lighter staining.