Final answer:
In the CRISPR/Cas9 system, guide RNAs are engineered by fusing spacer DNA, which is complementary to the target sequence, with tracrRNA to form a single guide RNA. This is then cloned into a CRISPR/Cas9 gene array on a plasmid.
Step-by-step explanation:
In the CRISPR/Cas9 system, the guide RNA (gRNA) or spacer RNA is produced by engineering a synthetic DNA sequence that is complementary to the target DNA region. This sequence is termed the spacer DNA. The engineered DNA also includes a Cas protein-specific sequence.
The next step is to fuse this spacer DNA with trans-activating RNA (tracrRNA) to create a single guide RNA (sgRNA). This sgRNA is then cloned into a CRISPR/Cas9 gene array on a plasmid, replacing the original spacer DNAs. Once the engineered plasmid is introduced into cells, the sgRNA forms a complex with the Cas9 protein. The sgRNA directs the Cas9 to the specific target DNA sequence, and then the Cas9 protein cleaves the DNA, leading to gene editing.
This system makes use of the natural immune defense mechanisms of bacteria, where phage-derived spacer DNAs in the CRISPR/Cas gene array act as memory sequences that guide the complex to counteract subsequent infections by the same phage. By understanding this mechanism, scientists have harnessed the power of Precision Gene Editing and applied it to living cells, creating unprecedented opportunities in genetic research and potential therapies for genetic disorders.