How Your Body Reads DNA (DNA to Protein)
Every trait you have is written in DNA, but DNA never leaves the nucleus. To build a body, your cells run a two-step copy machine called the central dogma. First they transcribe a gene into a portable message (mRNA), pairing each DNA base with its complement (A→U, T→A, G→C, C→G). Then a ribosome translates that message three letters at a time: for each codon, a matching tRNA brings one amino acid, and the chain grows and folds into a protein. Press Play to watch a real gene become a protein — or turn off Auto-run and use Step one codon to walk the bases through by hand.
What's happening
The Science in Plain Language
1. DNA is the master copy — it stays locked in the nucleus. Your genome is about 3 billion letters (bases: A, T, G, C) coiled into 46 chromosomes. It is far too precious to ship around the cell, so the cell makes disposable working copies instead of moving the original.
2. Transcription: DNA → mRNA. An enzyme called RNA polymerase latches onto the start of a gene, locally “unzips” the double helix, and reads one strand (the template) letter by letter. For each template base it adds the complementary messenger RNA (mRNA) base by a simple pairing rule: DNA A→U, T→A, G→C, C→G (RNA uses uracil, U, wherever DNA would use thymine). The finished mRNA reads the same as the gene's other, non-template “coding” strand — just with U in place of every T.
3. The message leaves the nucleus. The mRNA slips out through a nuclear pore into the cytoplasm, where the protein-building machines live.
4. Translation: mRNA → protein. A ribosome clamps onto the mRNA and reads it three letters at a time. Each triplet is a codon, and each codon specifies exactly one amino acid. Reading always begins at the start codon AUG (which codes for methionine), fixing the reading frame. With 4 letters read 3 at a time there are 64 possible codons mapping onto 20 amino acids plus stop signals — this mapping is the genetic code. It is redundant: most amino acids have several codons (for example GGU, GGC, GGA and GGG all mean glycine), which cushions the effect of many single-letter typos.
5. tRNAs deliver the right amino acids. For each codon, a transfer RNA (tRNA) whose three-base anticodon is complementary to that codon docks into the ribosome carrying the matching amino acid. The ribosome links that amino acid onto the growing chain with a peptide bond, the emptied tRNA leaves, and the ribosome ratchets forward exactly one codon. Repeat, residue by residue.
6. A stop codon ends the chain. Three codons — UAA, UAG and UGA — code for no amino acid at all. When the ribosome reaches one, no tRNA fits; instead a protein called a release factor slots in, the finished chain is cut free, and the ribosome subunits let go and recycle. In this animation the gene ends in UAA.
7. The chain folds into a working protein. The finished amino-acid chain folds into a precise 3-D shape — and that shape is the function. Hemoglobin that carries your oxygen, the enzymes that digest your food, the collagen in your skin, the antibodies in your blood: every one is a protein spelled out by a gene through exactly these two steps. Because the code is nearly universal across all life, a bacterium can even read a human gene. And because it is exact, a single wrong base can matter: changing one DNA letter in the β-globin gene swaps one amino acid (glutamate → valine) and produces sickle-cell hemoglobin. That is how genes become you — and how a one-letter typo can change a life.