The nucleotide linkage joining a 5′ phosphate to a neighboring 3′ hydroxyl is a __________ bond.

### Why this is right A phosphodiester bond connects the phosphate associated with one nucleotide’s 5′ position to the 3′ hydroxyl of another nucleotide. Repetition of this linkage forms the strand backbone. ### The concept The 5′ and 3′ labels refer to carbon positions in the pentose sugar. Their arrangement makes nucleic-acid strands directional, with distinct 5′ and 3′ ends. ### Terms - **Hydroxyl**: a functional group containing oxygen and hydrogen, written –OH. ### Remember A nucleic-acid backbone runs through alternating sugars and phosphates.