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How do ribose and deoxyribose form five-membered furanose rings in RNA and DNA?

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heterocyclic compound There are many different sulfur-containing heterocycles. One of the best known is thiophene, C₄H₄S, derivatives of which occur as plant pigments and as other natural products such as biotin.

In aqueous solution, sugars like ribose and deoxyribose do not exist solely as linear, open-chain structures. Instead, they exist as equilibrium mixtures of their open-chain and cyclized forms.12

These sugars form five-membered furanose rings—which possess the tetrahydrofuran ring system—through a process involving the addition of a hydroxyl group (-OH) from one of the carbon atoms to the carbonyl group (the aldehyde or ketone group) within the same molecule. This cyclization creates a hemiacetal structure.12

In the case of these pentose sugars, the cyclic form is the predominant structure found in RNA and DNA, the heredity-controlling components of living cells. The resulting cyclic structure features an anomeric carbon atom, and the configuration of the new hydroxyl group at this position determines whether the sugar is an alpha or beta anomer.312