Your genome
3 billionletters in one copy of the human genome
4chemical letters: A, T, C and G
~20,000genes that code for proteins
6 feetof DNA in a single cell, if stretched out
Most cells carry two copies, one from each parent.
From code to living thing
- DNA stores the recipeGenes are stretches of the four-letter code
- RNA copies a geneA working copy carries the message out
- Ribosomes read itThree letters at a time choose amino acids
- Proteins do the workBuilding tissue, digesting food, fighting germs
1953
Watson and Crick described the double helix, building on Rosalind Franklin's X-ray images.
What we know and don't
Known
- How DNA copies itself
- How genes become proteins
- The full human sequence, finished in 2003
Still unknown
- How the first living cells formed
- How the first self-copying molecules arose
- Whether life began elsewhere too
Sources: National Human Genome Research Institute; Nature
Remember
Four chemical letters, arranged in 3 billion steps, spell out a human being, but how life first began is still unsolved.
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Answer key
- How many letters does DNA's code use?4A, T, C and G.
- About how many letters are in one copy of the human genome?3 billionAbout 3 billion base pairs.
- What do genes mainly tell a cell to make?ProteinsGenes code for proteins that do most of the body's work.
- When was the Human Genome Project completed?2003The project finished its sequence in 2003.
- Which question is still unsolved?How life first beganThe origin of life remains an open question.