Genetics And Molecular Biology Practice Exam

Which molecules make up the sides of the DNA ladder?

Deoxyribose, Phosphate Ribose, Phosphate Deoxyribose, Sulfate Glucose, Phosphate

Correct Answer:

Ribose, Phosphate

Explanation:

DNA’s ladder sides are the sugar–phosphate backbone. In DNA, the sugar is deoxyribose, a five‑carbon sugar missing an oxygen at the 2′ position, and each sugar is connected to a phosphate group. These alternating deoxyrose and phosphate units form the phosphodiester backbone that runs along the length of the molecule, providing the structural rails for the double helix while the bases pair and form the rungs in the middle. So the sides are made from deoxyribose and phosphate. Ribose would be in RNA, not DNA, which is why it doesn’t fit DNA’s backbone.

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