Some bacteria possess a fascinating system for combatting viral infections calle

Question

Some bacteria possess a fascinating system for combatting viral infections called CRISPR (Clustered Regularly Interspersed Short Palindromic Repeats). The spacer DNAs (between the repeats) are actually sequences from viral genomes, that were copied and placed between the palindromic repeats during a viral infection. Through the action of the Cas enzymes, the viral sequences can be used to target viral RNA or DNA for destruction. DNA sequences from different viruses are retained and can be used as a defense against the viruses in the future. Modification of the CRISPR system allows for direct editing of any genome. What is the role of Cas9 in genome editing? A Cas9 joins the tracer and linker sequences into a single stranded RNA that is complementary to the target DNA B) Cas9 repairs double stranded breaks by nonhomologous end joining. C) Cas9 induces dicer to create multiple double strand copies of the DNA D) Cas9 binds to a complex of guide RNA and target DNA and introduces a double stranded break in the target DNA E Cas9 will interfere with transcription by modifying the structure of the RNA polymerase.

Explanation / Answer

Answer :- Option D is correct. Guide RNA attached to cas9 recognizes the DNA sequence and Cas 9 is used to cut the DNA at specific point. Once DNA is cut researchers use host cell's own repair machinery to add or remove the peices of genetic material or can also make changes to DNA by replacing the existing sequence with a custom made DNA sequence.

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