* Sugar-phosphate backbone: This backbone is formed by alternating sugar (deoxyribose) and phosphate groups. The sugar molecules are linked to each other by phosphate groups, creating a long chain.
* Two antiparallel strands: The two strands of DNA run in opposite directions, meaning the 5' end of one strand aligns with the 3' end of the other. This antiparallel arrangement is crucial for DNA replication and transcription.
In summary: The sides of a DNA double helix are composed of two sugar-phosphate backbones, running in opposite directions, that hold the nitrogenous bases together.
