Which two components form the sugar-phosphate backbone?

Which two components form the sugar-phosphate backbone?

• A. Sugar and base
• B. Phosphate and base
• C. Sugar and phosphate
• D. Bases only

Answer: (C)

The backbone of nucleic acids is made by alternating sugar molecules and phosphate groups, linked together by phosphodiester bonds. The sugar (deoxyribose in DNA) provides the backbone’s repeating structure, while the phosphate groups connect the sugars and give the molecule its directionality (5' to 3'). The bases—adenine, thymine, cytosine, and guanine (and uracil in RNA)—hang off the sugar as side groups and store genetic information, but they do not form the backbone itself. Therefore, the two components that form the sugar-phosphate backbone are the sugar and the phosphate.

The backbone of nucleic acids is made by alternating sugar molecules and phosphate groups, linked together by phosphodiester bonds. The sugar (deoxyribose in DNA) provides the backbone’s repeating structure, while the phosphate groups connect the sugars and give the molecule its directionality (5' to 3'). The bases—adenine, thymine, cytosine, and guanine (and uracil in RNA)—hang off the sugar as side groups and store genetic information, but they do not form the backbone itself. Therefore, the two components that form the sugar-phosphate backbone are the sugar and the phosphate.