CRISPR

In-depth explanation of CRISPR

CRISPR-Cas9 is a genome-editing tool adapted from a bacterial adaptive immune system that recognises and cuts invading viral DNA. In the engineered version, a guide RNA containing a sequence complementary to the target directs the Cas9 nuclease to the matching site in the genome. Cas9 makes a double-strand break that the cell repairs either by error-prone end joining, which often disrupts a gene, or by homology-directed repair, which can insert a designed sequence. The method is fast, inexpensive and works in many organisms. Edits to human germline cells raise serious ethical and safety concerns, and are restricted in many countries.

Going deeper: CRISPR

Key ideas: A bacterial adaptive immune system repurposed as a gene editor. A guide RNA of about 20 nucleotides directs the Cas9 nuclease to the matching DNA next to a PAM sequence (NGG for SpCas9), where it makes a double-strand break. The cell repairs by NHEJ (errors, gene knockout) or by HDR with a supplied template (precise edit).

Common mistakes and connections: Students think CRISPR is perfectly accurate; off-target cuts occur and are a safety concern. The enzyme is Cas9, CRISPR is the DNA repeat array. Newer base and prime editors change letters without full breaks. Links to ethics, gene therapy and RNA base pairing.

Visualization of CRISPR

CRISPR-Cas9 uses a guide RNA to find a matching sequence in the double helix and cut both strands there, allowing the gene to be disrupted or edited. The interactive lesson shows this as a live animation or chart.

Worked example and use case

A guide RNA matching a gene's coding sequence can switch that gene off by introducing a frameshift.

Where CRISPR fits in Biochemistry, Environment & Industry

CRISPR is topic 30 of 127 in Biochemistry, Environment & Industry.

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