Question

6) CRISPR-Cas9 and genome editing:

1. Briefly explain the prevailing hypothesis for the bacterial origins and function of CRISPR-Cas9 (prior to its use in genome engineering).
2. Identify and briefly explain 3 important technical issues that have been identified as major hurdles to conducting CRISPR on germline cells in humans (e.g., technical things we need to solve before it would ever be reasonable to make CRISPR babies, for example). For this question, we can ignore the  large number of ethical issues, and just focus on the technical ones.

Answer 1

CRISPRs – Cas9: (Clusters of Regularly Interspaced Short Palindromic Repeats). This is a specialized region of DNA having repeated nucleotide sequences and spacers. Cas9 protein binding enzyme which binds to two RNA molecule and cleaves the target site in foreign DNA. This CRISPR – Cas9 is naturally present in the bacterial genome editing system.

Streptococcus thermophiles is a bacteria widely used in dairy industries. During a viral attack, the bacteria takes a part of Viral DNA and create a CRISPR array. This array serves as a memory for future viral encounters. If the virus attacks again, RNA fragments are produced using CRISPR arrays to target viral DNA. Then the Cas9 protein helps to disable the virus by cleaving at the target site the DNA. PAM (Protospacer adjacent motif) is a short DNA sequence that serves as a tag for Cas9 protein in cleaving target DNA by placing itself adjacent to target DNA molecules. In this manner, Cas9 will not ever attack the CRISPR region rather than the viral region.