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In the sugar-phosphate backbone of a nucleic acid, the phosphate residue links:

AThe 5' carbon of one sugar to the 3' carbon of the next
BThe 1' carbon of one sugar to the 2' carbon of the next
CThe 2' carbon of one sugar to the 5' carbon of the next
DThe 3' carbon of one sugar to the 1' carbon of the next
Answer & Solution
Correct answer: A. The 5' carbon of one sugar to the 3' carbon of the next
1. Nucleotides are joined into a strand through their phosphate groups. 2. The phosphate attaches to the hydroxyl group of the 5' carbon of one sugar. 3. It also attaches to the hydroxyl group of the 3' carbon of the sugar of the next nucleotide. 4. That pairing forms the 5'-3' phosphodiester linkage. 5. The other options name carbons that do not carry the hydroxyls used in this bond. _Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 3 'Biological Macromolecules', sections 3.1-3.5_
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