Question

1. choose the best answer.

what forms the backbone of the dna molecule?
○ nitrogenous bases
○ sugar - phosphate groups
○ rna

1. choose the best answer.

what forms the rungs of the ladder on a dna molecule?
○ sugar - phosphate groups
○ nitrogenous bases
○ rna

1. choose the best answer.

what nitrogenous base always pairs with thymine?
○ guanine
○ cytosine
○ adenine

Explanation:

Question 5

DNA's structure is a double helix. The backbone is formed by alternating sugar (deoxyribose) and phosphate groups. Nitrogenous bases form the rungs, and RNA is a different nucleic acid, not part of DNA's backbone.

In the DNA double - helix (ladder - like structure), the rungs are formed by the pairing of nitrogenous bases (adenine - thymine, guanine - cytosine). Sugar - phosphate groups form the backbone, and RNA is not part of DNA's structure here.

In DNA base - pairing rules, adenine (A) always pairs with thymine (T), and guanine (G) pairs with cytosine (C). So the base that pairs with thymine is adenine.

Answer:

B. sugar - phosphate groups

Question 6