Chemistry Labs

Biochemistry and biomedical chemistry

Gene editing (CRISPR)

CRISPR–Cas systems turn guide-directed nucleic-acid recognition into a programmable genome-targeting tool.

1 Lower secondary2 Upper secondary3 Undergraduate4 Advanced5 Research

IntuitionIntuition: the central idea

CRISPR–Cas systems turn guide-directed nucleic-acid recognition into a programmable genome-targeting tool.

Explore the schematic model; it illustrates a concept rather than replacing experimental evidence.

SchoolSchool level: key concepts and a first application

Definition: Core concept

SpCas9 uses a guide RNA to pair with a target next to a PAM, then creates a double-strand break. NHEJ can introduce indels; HDR can use a donor template.

CRISPR systems inherited from bacterial adaptive immunity pair a guide RNA with a nuclease such as Cas9. The DNA double-strand break is resolved by cell repair: end-joining tends to knock genes out, homology-directed repair can write edits.

Key terms and meaning
TermInterpretation
Guide RNAA short RNA that directs Cas proteins to a complementary target.
PAMShort DNA motif next to the target required by many Cas nucleases.
HDRHomology-directed repair using a donor template.

Example: Apply the idea

Why can the same CRISPR nuclease produce different sequence outcomes in different cells?

Solution

The nuclease creates a lesion, but repair pathway choice, cell cycle, donor availability and local sequence context shape the final allele.

UndergraduateUniversity level: quantitative description

guide RNA+Cas9+PAM-adjacent target→DNA break\text{guide RNA}+\text{Cas9}+\text{PAM-adjacent target}\rightarrow\text{DNA break}

Editing outcome is not only about cutting: guide binding kinetics, PAM availability, chromatin accessibility and repair pathway biases all matter.

AdvancedAdvanced: assumptions and mechanistic detail

Beyond SpCas9, Cas12a, base editors, prime editors and epigenome editors offer different trade-offs: PAM range, nicking, double-strand breaks, precision and delivery constraints differ.

ResearchResearch frontier: open questions and current practice

References