An introduction
DNA
The molecule that carries life's instruction, written in a four-letter code three billion characters long.
What is DNA
Deoxyribonucleic acid is a long molecule that contains the genetic blueprint for every living organism. Found in nearly every cell, it encodes the information needed to build and maintain an organism from a single fertilized egg through adulthood. The complete set of DNA in a cell is called its genome, and the human genome contains roughly three billion base pairs of information.
The Double Helix
DNA's structure is a double helix - two strands wound around each other like a twisted ladder. Each strand is made of a sugar-phosphate backbone with chemical bases attached. The bases pair up in the middle with exquisite specificity: adenine always bonds with thymine, and guanine with cytosine. This complementary pairing is the key to how DNA can be copied accurately, generation after generation.
How DNA Works
Before a cell divides, its DNA copies itself in a process called replication. The two strands unwind and each serves as a template for a new complementary strand, producing two identical copies. For a cell to use its stored information, it transcribes specific genes into messenger RNA. This RNA is then translated into proteins - the molecular machines that carry out the cell's work. This flow of information, from DNA to RNA to protein, is the central dogma of molecular biology.
The Four-Letter Code
The DNA code is written in just four letters: A, T, G, C. These bases combine into 64 possible three-letter codons, each specifying one of twenty amino acids or a stop signal. The genetic code is nearly universal - the same codons code for the same amino acids in humans, bacteria, and oak trees. From these twenty amino acids, life builds everything: enzymes that digest food, collagen that structures skin, antibodies that fight infection.
Why It Matters
Understanding DNA has transformed medicine, agriculture, and forensics. Gene therapies can correct inherited disorders by delivering working copies of a faulty gene. CRISPR editing allows scientists to rewrite specific genes with precision. DNA sequencing can identify pathogens, trace ancestry, and personalize cancer treatments. Reading and writing the language of life is reshaping our world, one base pair at a time.
The Central Dogma
Information flows through the cell in one direction: from stored DNA to working RNA to functional protein. This three-step process is how every gene expresses itself.
Replication
DNA copies itself before cell division
Transcription
A gene is read into messenger RNA
Translation
RNA is decoded into a protein
3B
base pairs in the human genome
99.9%
of DNA shared between any two people
46
chromosomes in each human cell
2m
length of DNA in a single cell, stretched
DNA
An introduction
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