The polynucleotide has directionality from 5’
(phosphate group) end to 3’ (-OH group) end
what does this mean? can anyone explain what is 5' and 3'? .??

Question

The polynucleotide has directionality from 5’
(phosphate group) end to 3’ (-OH group) end
what does this mean? can anyone explain what is 5' and 3'? >.>??

blues · Answer

The 5' and 3' refer to carbons 5 and 3 in the deoxyribose sugars in the DNA backbone.

Basically, the DNA backbone is made of alternating phosphate and sugar (deoxyribose) groups. When nucleotides are added to the chain, the newly incorporated phosphate group is covalently attached to the 3' hydroxyl group on the last base already in the chain. At the start of the DNA molecule, there is a nucleotilde with an unbonded phosphate group on the 5' deoxyribose; at the newly synthesised end, there is a DNA molecule with an unbound hydroxyl group on the 3' carbon of the deoxyribose.

Clear?