Summary Primary structure of nucleic acid

Primary structure of Nucleic acid
What is a nucleotide?
• Forms DNA and RNA
• Composition: pentose sugar (ribose/deoxyribose) + phosphate + organic nitrogenous base (H receiver)


Nucleotide sugars

RNA DNA

Pentose sugar Deoxyribose sugar


5 membered ring with 5 membered ring with
1'C linked by Oxygen to -H on 2'C rather and
4'C and 5'C attached as -OH
a side chain to 4'C



• Electron density on oxygen repels atoms so
2’C or 3’C is out of plane
• Not planar as the planar ring is subject to steric
strain




Nucleotide phosphate
• Free nucleotides have phosphate groups attached at 5'C via phosphoester bond (P-O-C)
• Determines the acidic nature of nucleotides

Different phosphate groups:
• 1 phosphate: nucleotide monophosphate (AMP)
• 2 phosphate: nucleotide diphosphate (ADP)
• 3 phosphate: nucleotide triphosphate (ATP)
• γ-phosphate usually donated
• α-phosphate forms the phosphodiester bond



Adenosine-5'-triphosphate (ATP)→Deoxyadenosine-5'C-triphosphate (dATP)


Nucleotide base
• 1'C of sugar joined to the base by β-glycosidic linkage via condensation (base above the plane of sugar)
• Forms PLANR ring (electrons of all atoms delocalised)
• 2 types: Purine and pyrimidine


Purine Pyrimidine
Double ring:
5 membered ring fused Single 6-membered ring
with 6 membered ring

Adenine (A), Guanine (G) Cytosine (C), Thymine (T), Uracil (U)




Purine