Which two types of molecules form the backbone of a DNA strand?

• A. Guanine and cytosine
• B. Deoxyribose sugar and phosphate group
• C. Ribose sugar and uracil
• D. Adenine and thymine

Answer: (B)

Verified step by step guidance

1. Understand the structure of a DNA strand, which consists of a repeating backbone and nitrogenous bases attached to it.
2. Recall that the backbone of DNA is made up of alternating sugar and phosphate groups, which provide structural support.
3. Identify the sugar in DNA as deoxyribose, a five-carbon sugar lacking one oxygen atom compared to ribose found in RNA.
4. Recognize that the phosphate groups link the deoxyribose sugars together through phosphodiester bonds, forming the continuous backbone.
5. Conclude that the two types of molecules forming the DNA backbone are the deoxyribose sugar and the phosphate group.