DNA, or deoxyribonucleic acid, is the molecule that carries genetic instructions in almost all living organisms.
Structure
DNA is a double helix: two strands wound around each other. Each strand is a chain of units called nucleotides, and each nucleotide contains one of four bases — adenine (A), thymine (T), guanine (G) and cytosine (C).
The strands are complementary: A always pairs with T, and G always pairs with C. This pairing is what allows the molecule to be copied accurately.
From gene to protein
A gene is a segment of DNA that codes for a product, usually a protein. The process runs in two stages:
- Transcription — the DNA sequence is copied into messenger RNA.
- Translation — ribosomes read the RNA in groups of three bases and assemble the corresponding chain of amino acids.
Proteins then fold into shapes that determine their function, from digesting food to carrying oxygen.
Mutation and variation
Copying is highly accurate but not perfect. Changes in sequence — mutations — may have no effect, may cause disease, or may occasionally be advantageous. Accumulated variation across populations is the raw material of evolution.
Applications
- Medicine — diagnosing inherited conditions, targeting treatment to a patient's genetics.
- Forensics — identification from biological traces.
- Agriculture — selecting and modifying crop traits.
- Ancestry and history — reconstructing population movements.
Ethical dimension
The ability to read and edit genetic information raises questions that are not technical: consent for genetic testing, privacy of genomic data, and the limits of editing human embryos. These debates are ongoing and regulated differently across countries.