DNA forms by condensation polymerisation
The backbone of DNA is based on a repeated pattern of a sugar group and a phosphate group.
The full name of DNA, deoxyribonucleic acid, gives you the name of the sugar present - deoxyribose.Deoxyribose is a modified form of another sugar called ribose. Ribose is the sugar in the backbone of RNA, ribonucleic acid.
The sugar phosphate backbone is formed by condensation polymerisation. The lone pairs of electrons on an oxygen atom in the deoxyribose sugar molecule makes a dative covalent bond with the phosphorous atom in a phosphate group.
A molecule of water is lost and a phosphate-ester link is formed. There are still OH groups in the phosphate-ester, so further ester links can be formed.
It is also a condensation reaction that connects base molecules to sugars in the sugar-phosphate backbone.
All of the bases have an NH group in their structure.
It’s the N atom of the NH group that bonds to deoxyribose –eliminating an OH group from the sugar and H from the NH to form water.
Drafted by Eunice (Chemistry)