Two antiparallel chains
A DNA molecule contains two polynucleotide strands. Each strand has a repeating sugar-phosphate backbone in which deoxyribose sugars and phosphate groups are linked by phosphodiester bonds.
The two strands run in opposite directions and are therefore described as antiparallel. One runs from 5′ to 3′, while the other runs from 3′ to 5′.
- Phosphodiester bonds link neighbouring nucleotides within each strand.
- Each strand has a 5′ end and a 3′ end.
- The two strands are arranged in opposite orientations.
- The nitrogen-containing bases project from the backbones towards the inside of the DNA molecule.
5′ → 3′ opposite to 3′ → 5′