Apentix/AP Biology/Unit 6: Gene Expression and Regulation/Question
AP Biologyeasymcq1 pt

In CRISPR-Cas9 gene editing, which engineered component directs the Cas9 protein to cut at one chosen genomic location?

A.A guide RNA designed to base pair with the target sequence at that location
B.A restriction enzyme attached permanently to the surface of Cas9
C.An antibiotic resistance marker included with the editing mixture
D.A heat treatment step that denatures DNA only at the chosen site

Explanation

Core Concept

Cas9 is an endonuclease whose DNA binding depends on Watson-Crick pairing between a guide RNA and one genomic strand. Researchers design the twenty nucleotide guide segment to complement the chosen locus, so the complex binds there and Cas9 cuts both strands. Swapping the guide RNA retargets the same protein to new sites. Specificity therefore comes from RNA-DNA base pairing, not from the protein alone.

Correct Answer

AA guide RNA designed to base pair with the target sequence at that location

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