Advanced Placement (AP) Biology Practice Exam

What type of bond is formed between nucleotides in a strand of RNA or DNA?

1. Hydrogen bond

2. Peptide bond

3. Phosphodiester bond

4. Ionic bond

The correct answer is: Phosphodiester bond

Nucleotides in a strand of RNA or DNA are linked together by phosphodiester bonds. This type of bond forms when the phosphate group of one nucleotide connects to the hydroxyl group on the sugar of another nucleotide, creating a sugar-phosphate backbone that is characteristic of nucleic acid structures. This linkage is essential for the stability and integrity of the nucleic acid strand, allowing it to maintain its structure and function within the cell. In RNA and DNA, the sequence of the nucleotides, connected by these phosphodiester bonds, encodes genetic information. The alternating sugar and phosphate groups form a robust backbone, while the varied nitrogenous bases (adenine, thymine, cytosine, guanine in DNA; adenine, uracil, cytosine, guanine in RNA) are attached to the sugar molecules, projecting out from the backbone and providing the specific coding for genetic information. Other types of bonds mentioned, like hydrogen bonds and ionic bonds, play roles in the interaction and stability of complementary base pairs and tertiary structures but are not responsible for the direct linkage of nucleotides to form the backbone of RNA or DNA strands. Peptide bonds, on the other hand, are specific to proteins and link amino acids