DNA
Definition and meaning of DNA in chemistry.
DNA (deoxyribonucleic acid) is a macromolecular biopolymer consisting of two antiparallel polynucleotide chains that coil around each other to form a right-handed double helix. The molecule carries the complex genetic instructions required for the development, functioning, growth, and reproduction of all known living organisms and many viruses.
In more detail
DNA consists of repeating structural units called nucleotides, which each contain a five-carbon deoxyribose sugar, a phosphate group, and a nitrogen-containing nucleobase. The four primary nucleobases are adenine, cytosine, guanine, and thymine. The structural backbone of the DNA strand is formed by alternating sugar and phosphate groups connected by strong covalent phosphodiester bonds linking the 3' carbon of one sugar to the 5' carbon of the next. The two independent strands are held together by non-covalent hydrogen bonds between complementary base pairs, where adenine specifically pairs with thymine via two bonds and cytosine pairs with guanine via three bonds. This precise base-pairing mechanism allows DNA to replicate itself accurately during cell division, ensuring strict genetic continuity across generations. The linear sequence of these chemical bases encodes the biological information that is subsequently transcribed into messenger RNA and translated into functional proteins through the central dogma of molecular biology.
Key facts
| Field | Biochemistry |
|---|---|
| Monomer unit | Deoxyribonucleotide (sugar, phosphate, nucleobase) |
| Primary bases | Adenine (A), Cytosine (C), Guanine (G), Thymine (T) |
| Molecular structure | Right-handed antiparallel double helix |
| Primary function | Long-term storage and transmission of genetic information |
The complete human genome consists of approximately 3.2 billion base pairs of DNA securely organized into 23 pairs of chromosomes within the cell nucleus, encoding roughly 20,000 unique protein-coding genes.
Frequently asked questions
How does DNA structurally differ from RNA?
DNA contains the sugar deoxyribose and the nucleobase thymine, and it typically exists as a highly stable double-stranded helix. RNA contains the sugar ribose with an extra hydroxyl group, utilizes the base uracil instead of thymine, and usually functions as a single-stranded molecule.
What defines the directionality of a DNA strand?
A single DNA strand has an asymmetric structure with a 5' end terminating in a free phosphate group and a 3' end terminating in a free hydroxyl group. The two strands in a double helix run in opposite directions, known as an antiparallel orientation, which is critical for DNA polymerase function during replication.