Question

if we think of the dna double helix as a twisted ladder, what makes up the rungs or steps of the ladder? multiple choice phosphate groups and bases purines and pyrimidines sugars only phosphate groups only alternating phosphate groups and sugars

Explanation:

In the DNA double - helix structure, the rungs of the "ladder" are made up of base pairs. Bases include purines (adenine and guanine) and pyrimidines (thymine and cytosine), which pair with each other through hydrogen bonds.

Answer:

B. Purines and pyrimidines