Question

The backbone of dna (i.e., sides of the dna "ladder") consists of

Answer 1

Alternating phosphate and sugar residues

Answer 2

The structure of DNA consists of three main molecules-

1. Nucleotides

2. Sugar

3. Phosphate

Now, nucleotides are present on the inner side of the DNA strand, the sides or the backbone of DNA is made of the other two molecules, i.e. sugar and phosphate. The structure looks like the image shared below. One carbon atom of the sugar molecule is connected to nucleotide, and two carbons are connected to phosphates at two sides. This way a chain or the backbone of DNA is formed.