Covalent bonds in DNA occur within each single strand, specifically linking the components of the nucleotide units. These covalent bonds:
- Connect the sugar (deoxyribose) and phosphate groups of adjacent nucleotides through phosphodiester bonds, forming the sugar-phosphate backbone of each DNA strand. This bond links the 3' carbon of one sugar to the 5' carbon of the next nucleotide's sugar via a phosphate group
- Also hold together the atoms within each nucleotide, bonding the sugar to its attached nitrogenous base and phosphate group
In contrast, the two DNA strands in the double helix are held together by hydrogen bonds between complementary nitrogenous bases (adenine-thymine and cytosine-guanine), not covalent bonds
. Thus, covalent bonds occur within each linear DNA strand, maintaining the integrity of the sugar-phosphate backbone and the nucleotide structure itself, while hydrogen bonds connect the two strands across the helix.
