Question

The double-helix model of DNA resembles a twisted ladder in which the rungs of the ladder are ______.

Options

• sugar-phosphate paired with sugar-phosphate

• A paired with G and C paired with T

• a purine paired with a pyrimidine

• both sugar-phosphate paired with sugar-phosphate and A paired with G and C paired with T.

Answer 1

Both sugar-phosphate paired with sugar-phosphate and A paired with G and C paired with T.

The double-helix model of DNA resembles a twisted ladder in which the rungs of the ladder are sugar-phosphate paired with sugar-phosphate and paired with G and C paired with T.

Explanation:

The rungs of the DNA ladder represent the complete horizontal units that bridge the two sides of the double helix. This structure is formed by the sugar-phosphate framework anchoring each base to the backbone, while the four nitrogenous bases (A, G, C, and T) meet in the centre to complete the connection. By including both the chemical backbone units and the specific pairing bases, the model describes the entire assembly that creates a stable and functional “step” in the genetic code.