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Describe the structure of polynucleotide chain of DNA or RNA ?
Solution

A nucleotide is composed of a nitrogenous base, pentose sugar and phosphate group.
Pentose Sugar : Two types of sugar are present a given below : $(a)$ Ribose (in case of $RNA$) $(b)$ Deoxyribose (in case of $DNA$).
Nitrogenous Base : It is a nitrogen containing organic molecule having similar physical properties of a base.
There are two types of nitrogenous bases : $(a)$ Purines (Adenine and Guanine).$(b)$ Pyrimidines (Cytosine, Uracil and Thymine) Out of the Pyrimidins, Cytosine is common for both $DNA$ and $RNA$, while Thymine is present in $DNA$ and Uracil is present in $RNA.$
A nitrogenous base is linked to the pentose sugar through a $N$-glycosidic linkage to form a nucleoside, such as adenosine or deoxyadenosine, guanosine or deoxyguanosine, cytidine or deoxycytidine and uridine or deoxythymidine.
When a phosphate group is linked to $5^{\prime}-\mathrm{OH}$ of a nucleoside through phosphoester linkage, a corresponding nucleotide (or deoxynucleotide depending upon the type of sugar present) is formed.
Two nucleotides are linked through $3^{\prime}-5$ ' phosphodiester linkage to form a dinucleotide.
– More nucleotides can be joined in such a manner to form a polynucleotide chain.
A polymer thus formed has at one end a free phosphate moiety at $5^{\prime}$-end of ribose sugar, which is referred to as $5^{\prime}$-end of polynucleotide chain.
Similarly, at the other end of the polymer the ribose has a free $3^{\prime}-$ $OH$ group which is referred to as $3$ '-end of the polynucleotide chain.
The backbone in a polynucleotide chain is formed due to sugar and phosphate.
The nitrogenous bases linked to sugar moiety project from the backbone.
In RNA, every nucleotide residue has an additional -$OH$ group present at $2^{\prime}$-Position in the ribose.
Also, in $RNA$ the uracil is found at the place of thymine ($5$-methyl uracil, another chemical name for thymine).
Similar Questions
Match List$-I$ with List$-II :$
List$-I$ | List$-II :$ |
$a$ Bacteriophage $\phi \times 174$ | $i$ $48502$ base pairs |
$b$ Bacteriophage lambda | $ii$ $5386$ nucleotides |
$c$ Escherichia coli | $iii$ $3.3 \times 10^9$ base pairs |
$d$ Haploid content of human $DNA$ | $iv$ $4.6 \times 10^6$ base pairs |