The CRISPR-associated enzyme Cas9 __________ .


a. cuts RNA at a specific nucleotide sequence
b. cuts DNA at a specific nucleotide sequence
c. is likely derived from a bacteriophage
d. All of the above are correct.

Verified step by step guidance

1. Understand the role of Cas9 in the CRISPR system: Cas9 is an enzyme associated with the CRISPR adaptive immune system found in bacteria and archaea, which helps defend against invading genetic elements like viruses.
2. Recall that Cas9 is a nuclease that targets nucleic acids based on a guide RNA sequence that directs it to a complementary DNA sequence.
3. Recognize that Cas9 specifically binds to and cleaves double-stranded DNA at a site determined by the guide RNA, not RNA itself.
4. Consider the origin of Cas9: it is encoded by bacterial genomes as part of the CRISPR-Cas system, not derived from bacteriophages (viruses that infect bacteria).
5. Based on these points, determine which option correctly describes Cas9's function and origin by comparing each choice to the known characteristics of Cas9.

Key Concepts

CRISPR-Cas9 System

The CRISPR-Cas9 system is a bacterial adaptive immune mechanism that uses the Cas9 enzyme guided by RNA to target and cut specific DNA sequences. It allows precise editing of genetic material by creating double-strand breaks at defined locations.

Function of Cas9 Enzyme

Cas9 is an endonuclease that specifically cuts double-stranded DNA at sequences complementary to its guide RNA. It does not cut RNA, but uses RNA as a guide to locate the target DNA for cleavage.

Origin of Cas9

Cas9 is derived from bacteria and archaea as part of their defense against viruses, not from bacteriophages themselves. It evolved to recognize and destroy invading viral DNA, providing immunity to the host organism.