Question

Write the structures of fragments produced on complete hydrolysis of 𝐷𝑁𝐴. How are they linked in 𝐷𝑁𝐴 molecule? Draw a diagram to show pairing of nucleotide bases in double helix of 𝐷𝑁𝐴.

Answer 1

Structures of fragments produced on complete hydrolysis of $DNA$

$\bullet$ Complete hydrolysis of $DNA$ yields a pentose sugar (Deoxyribose), phosphoric acid and nitrogen containing heterocyclic compounds, called bases.


$DNA$ contains four nitrogen bases which are Adenine $\left(A\right)$, Guanine $\left(G\right)$, Cytosine $\left(C\right)$ and Thymine $\left(T\right)$.




Linkage of the different fragments in the structure of DNA

$\bullet$ A nucleoside is formed by the attachment of a base to $1$’- position of sugar.

$\bullet$ The sugar carbons are numbered as $1^{\prime },2^{\prime },3^{\prime }$


$\bullet$ A nucleotide is formed when the nucleoside is linked to the phosphoric acid at 5’-position of the sugar moiety.


$\bullet$ Nucleotides are joined together by phosphodiester linkage between 5’ and 3’ carbon atoms of the pentose sugar.


$\bullet$ Simplified version of nucleic acid chain


Pairing of nucleotide bases in double helix of $DNA$.

$\bullet$ James Watson and Francis Crick discovered the double strand helix structure of DNA.

$\bullet$ Two nucleic acid chains are wound about each other and held together by hydrogen bonds between pairs of bases. The two strands are complementary to each other because the hydrogen bonds are formed between specific pairs of bases.

$\bullet$ ​Adenine forms 2 hydrogen bonds with thymine, can be represented as $(A=T)$


$\bullet$ Cytosine forms 3 hydrogen bonds with guanine, can be represented as $(G\equiv C)$.



Diagram showing the pairing of nucleotide bases in double helix structure of $DNA$.

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