Nucleic Acids and Molecular Structure

Vocabulary flashcards covering electronegativity, charges, nucleic acids, nucleotides, sugars, bases, and the primary/secondary structure concepts of DNA and RNA.

Partial charge

A nonuniform distribution of electron density in a molecule leading to small, local positive and negative regions (e.g., oxygen partially negative, hydrogens partially positive).

Full charge

An integer net charge on an atom or molecule after electron transfer (e.g., an ion such as O2− in a negatively charged species).

Electronegativity order (O > N > C ~ H)

Oxygen is most electronegative, followed by nitrogen, with carbon and hydrogen having similar, comparatively lower electronegativities; affects charge distribution in molecules.

Hydrogen bond

A stabilizing interaction where a hydrogen attached to a highly electronegative atom (N or O) is attracted to a lone pair on another electronegative atom (often another N or O).

Nonpolar bond

A bond in which electrons are shared nearly equally between atoms of similar electronegativity, such as C–H bonds.

Nucleic acid

A polymer comprised of nucleotide monomers; the two main types are DNA and RNA.

Nucleotide

The monomer of DNA/RNA consisting of a phosphate group, a five‑carbon sugar, and a nitrogenous base.

Phosphodiester bond

Covalent bond linking the phosphate of one nucleotide to the 3′ carbon of the sugar of the next nucleotide, forming the backbone of nucleic acids.

Five prime end (5′ end)

End of a nucleic acid with a phosphate attached to the 5′ carbon of the sugar; synthesis typically adds to the 3′ end.

Three prime end (3′ end)

End of a nucleic acid with a hydroxyl group on the 3′ carbon of the sugar.

Deoxyribose

Five‑carbon sugar in DNA lacking an oxygen on the 2′ carbon (2′ deoxy), distinguishing DNA from RNA.

Ribose

Five‑carbon sugar in RNA that has an −OH on the 2′ carbon.

DNA (deoxyribonucleic acid)

Genetic material that stores information; typically double‑stranded and uses deoxyribose sugars.

RNA (ribonucleic acid)

Nucleic acid involved in expressing genetic information; uses ribose sugar and, in most cases, thymine is replaced by uracil.

Purines

Nucleobases with a two‑ring structure: adenine (A) and guanine (G).

Pyrimidines

Nucleobases with a single ring: cytosine (C) and thymine (T) in DNA; uracil (U) in RNA.

Base pairing rules

A pairs with T in DNA (A pairs with U in RNA); G pairs with C; hydrogen bonds stabilize the pairs (A–T with 2 H‑bonds; G–C with 3 H‑bonds).

Antiparallel

DNA strands run in opposite 5′ to 3′ directions relative to each other, enabling proper base pairing.

Complementarity

The property that bases pair in a specific way (A–T/U and G–C) to form stable double‑stranded nucleic acids.

Primary structure (nucleic acids)

The linear sequence of bases along a single strand of DNA or RNA.

Secondary structure (nucleic acids)

The higher‑order shapes formed by nucleic acids, such as the DNA double helix or tRNA cloverleaf structures.

Nucleoside

A base bound to a sugar (no phosphate).

Nucleobase

The nitrogenous base component of a nucleotide (A, C, G, T, or U).