purines and pyramidens,the chemical composition of genetic materials mainly the presence of purins...
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Chemical Structure Of Purines & Pyrimidines
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Nitrogenous bases of nucleic acid Nitrogenous bases of nucleic acids are heterocyclic , nitrogen
containing organic compounds They are 2 kinds
1. Purines2. Pyrimidines
Commonest purines of DNA & RNA 1. Adenine ( A )2. Guanine ( G )
Pyrimidines of DNA & RNA1. Cytosine ( C )2. Thymine( T )3. Uracil ( U ) in RNA Thymine is replaced by
Uracil
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Pyrimidines and Purines Pyrimidine and purine are the names of the parent
compounds of two types of nitrogen-containing heterocyclic aromatic compounds.
N
N
N
N
N
NH
Pyrimidine Purine
Benzene- type ring
Imidazol ring
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Purines
Purines are dicyclic ( double ringed ) molecules . Formed by the fusion between a six membered benzene – type ring &
a five membered imidazole ring. Carbon atoms in positions 4 & 5 are common for both rings. The dicyclic ring has N in positions 1 , 3 , 7 & 9. In nucleic acid N-9 of the purines links with the C-1 of sugar through
glycosidic bonding and form a purine nucleoside.
Adenine is a 6- amino purine ( -NH2 group at position 6 ) Guanine is a 2- amino,6- hydroxyl purine ( -NH2 group at 2nd
position , and an –OH group at 6th position.
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Important Purines Adenine and guanine are the principal purines of both
DNA and RNA.
Adenine
N
N
NH2
N
NH
Guanine
OH
HN
NH
N
N
H2N
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Pyrimidines
Pyrimidines are monocyclic ( single ringed ) molecule Formed 6 membered benzene – type ring N-3 of the pyrimidine links with the C-1 of sugar through
glycosidic bonding and form a pyrimidine nucleoside.
Cytosine is a 2- hydroxyl, 6- amino pyrimidine Thymine is a 2,6- dihydroxy , 5- methyl pyrimidine Uracil is a 2,6 – dihydroxy pyrimidine
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One of the fundamental properties of nucleic acid bases is their ability for hydrogen bonding between themselves.
It is also important that thymine and uracil can exist in the keto and enol tautomeric forms.
Tautomerism refers to the migration and rearrangement of hydrogen atoms within the molecule .
The tautomeric forms are responsible for the ionic properties of bases.
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Thank you
byAnand P P