4.5. THE NUCLEOTIDES

• DNA and RNA are long polymers whose monomer units are called nucleotides
• A nucleotide consists of:
• Nitrogen containing heterocyclic base
• Purine
• Pyrimidine
• Five-carbon sugar ring
• Ribose
• Deoxyribose 
•  Phosphoryl group
• Ring structures are found in both the base and the sugar
• Base rings are numbered as usual
• Sugar ring numbers are given the designation ' or prime
• Covalent bond between the sugar and the phosphoryl group is a phosphoester bond
• Bond between the base and the sugar is a b-N-glycosidic linkage joining the 1'-carbon of the sugar and a nitrogen atom of the base
• A nucleotide is the repeating unit of the DNA or RNA polymer
• The nitrogen base is attached b to
• ribose  (RNA)
• deoxyribose (DNA)
• The sugar is phosphorylated at carbon 5'