# Explain how the structure of RNA differs from that of DNA in ways that make RNA suited to its diverse functional roles in the cell.

> IB DP Biology Higher Level (2023 syllabus) — A1.2 Nucleic acids · Explain · 4 marks

## Mark scheme (4 marks)

1. RNA is single-stranded whereas DNA is double-stranded, allowing RNA to fold into complex three-dimensional shapes that underpin catalytic or structural functions.
2. RNA contains ribose (with a 2′-hydroxyl group) rather than deoxyribose, which increases flexibility but reduces chemical stability, making RNA suitable for transient / short-lived roles.
3. RNA contains uracil in place of thymine; uracil lacks the methyl group of thymine and is incorporated without the energy cost of methylation, consistent with RNA being synthesised in large quantities and turned over rapidly.
4. The variety of RNA types (mRNA, tRNA, rRNA, small regulatory RNAs) reflects that RNA structure can be adapted for information transfer, amino acid transport, catalysis, or gene regulation, illustrating the versatility conferred by its single-stranded, folding-capable structure.

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