Here's a breakdown:
* Sugar-phosphate backbone: This forms the structural framework of the DNA molecule. It consists of alternating sugar (deoxyribose) and phosphate groups.
* Nucleotides: Each nucleotide is composed of a sugar molecule, a phosphate group, and a nitrogenous base.
* Nitrogenous bases: These are the "rungs" of the DNA ladder. There are four types: adenine (A), thymine (T), guanine (G), and cytosine (C).
Specifically:
* The sugar and phosphate groups are located on the outside of the double helix, forming the backbone.
* The nitrogenous bases are located on the inside of the double helix, facing each other and forming the "rungs" of the ladder. They are linked by hydrogen bonds.
So, the nucleotides are not directly "on" the double helix, but rather they are the components that make up the double helix structure.
