Advanced Placement (AP) Biology Practice Exam

What type of structure does RNA have?

1. Nucleic acid

2. Single helix

3. Double helix

4. Triple helix

The correct answer is: Single helix

RNA is classified as a nucleic acid, which is a broad category that includes both DNA and RNA. While it consists of a long chain of nucleotides, the crucial distinction lies in its structure. RNA typically exists in a single-stranded form, which means that it does not organize into the double-helical structure characteristic of DNA. The single-stranded nature of RNA is significant because it allows RNA to fold into various shapes and perform diverse functions, such as acting as a messenger (mRNA) or a catalyst (ribozymes), which are essential in the processes of transcription and translation in protein synthesis. The mention of RNA having a double or triple helix does not align with its primary structure under normal biological conditions, as these forms would imply more complex interactions that are rarely present in functional RNA. The structural simplicity of the single helix enables it to interact readily with other molecules, facilitating its role in cellular processes. Therefore, recognizing RNA as a single helix encapsulates an essential characteristic that underpins its biological functions.