CRISPR: A Bacterial Defence Turned into a Tool
Bacteria keep fragments of past invaders in an array and use transcripts of those fragments to guide a nuclease to matching sequences. Supplying a guide of our own choosing turns the same system into a way of cutting a chosen site in any genome.
What a learner can do afterwards
- Explains how the array records past infections and how that record is used.
- Says what decides where the nuclease cuts, and what stops it cutting the array itself.
- Links the cut to a genome edit through the repair route the cell then uses.
1 · Read
CRISPR began as a bacterial filing system for past infections. After surviving a virus attack, the cell stores a short fragment of the invader in a repeating array. Those stored spacers are copied into guide RNAs that lead a nuclease to any matching sequence, so defence already knows how to find an address.
Supplying a guide of our own choosing redirects the same machinery to a site we pick in any genome. The guide sequence decides the cut: it pairs with its match and the nuclease cuts there. The stored array itself is spared because its fragments sit without the extra signal the nuclease needs beside a true target, while lookalike sites elsewhere risk off target cuts.
A cut alone is not yet an edit. The cell repairs the break, and the repair route decides the outcome: quick patching disrupts the site, while templated repair installs a designed sequence. Editing skill is mostly repair management, and retargeting needs only a new guide RNA rather than a rebuilt protein, which is why the tool spread so fast.
To plan an edit, design the guide for the address, check the nearest lookalikes, and choose the repair route for the outcome.
Guides pick the address, the nuclease cuts, and the cell repair writes the change.
2 · Watch
Take it off screen
Where it sits
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.