plz explain phosphoester and phosphodiester bond..? and whay do you mean that phosphate group attaches to 5'-OH of nucleoside to form nucleotide..???


This is a nucleoside composed of a purine or a pyrimidine base and a ribose or deoxyribose sugar. When a phosphate group binds to the OH group present at the carbon at 5th position 

(CH2OH) of sugar it is called a Nucleotide. 

The bond formed between the sugar and the phosphate group is a phosphoester bond but when this phosphate group forms a bond with another hydroxyl group of a sugar molecule it is called as phosphodiester bond because two ester bonds are involved.

The phosphate group here forms a diester bond.

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