The Structure of RNA

Ribose Sugar: The pentose sugar in RNA is ribose, which possesses a hydroxyl ($-OH$) group on the $2'$ carbon atom. This extra oxygen atom makes RNA more chemically reactive and less stable than DNA.

Nitrogenous Bases: RNA utilizes four bases: Adenine (A), Guanine (G), Cytosine (C), and Uracil (U). Uracil is structurally similar to thymine but lacks a methyl group.

Base Pairing: In regions where RNA folds, complementary base pairing occurs via hydrogen bonds: Adenine pairs with Uracil ($A=U$) and Guanine pairs with Cytosine ($G\equiv C$).

Intra-strand Pairing: Although single-stranded, RNA molecules often undergo internal base pairing where complementary sequences within the same strand bond together.

Structural Motifs: This folding creates complex shapes such as hairpin loops, bulges, and stems. These structures are critical for the molecule's stability and biological activity.

3D Conformation: The final three-dimensional (tertiary) shape of an RNA molecule, such as the cloverleaf shape of tRNA, is essential for its specific role in the cell, such as recognizing genetic codes.

Identify the Sugar: Always check the $2'$ carbon; the presence of an $-OH$ group is the definitive chemical signature of RNA in molecular diagrams.

Base Substitution: Remember that Uracil is the functional equivalent of Thymine; when transcribing from DNA to RNA, every 'A' on the DNA template pairs with a 'U' in the RNA transcript.

Structure-Function Link: Be prepared to explain how the single-stranded nature of RNA allows it to fold into shapes like tRNA, which is impossible for the rigid DNA double helix.

Stability Comparison: If asked why DNA is the primary genetic material, cite the absence of the $2'$ $-OH$ group, which makes DNA less susceptible to hydrolysis than RNA.