The Curious Case of CRISPR-Cas9

Hello! My name is Rishi Anarkat, and welcome to our first journey along The Hitchhiker’s Guide to Medicine. Today, we will cover one of my favorite subjects in Biomedical and genetic engineering, the CRISPR-Cas9 system.

The CRISPR-Cas9 system is one of the most popular methods of biomedical engineering, specifically genetic engineering, for altering one’s DNA. Utilizing the immune defense systems of prokaryotic(single celled) organisms, CRISPR-Cas9 provides engineers and scientists to accurately snip and insert nucleotide and codon(3 nucleotides) bases.

CRISPR, or Clustered Regularly Interspaced Short Palindromic Repeats, is a natural mechanism found in bacteria and archaea that they use to protect themselves from viruses. This system works by storing segments of viral DNA in their own genome in the CRISPR array. When the bacteria encounters the virus again, it uses this stored DNA as a template to recognize and defend against the virus.

The Cas9 protein is a crucial component of this system. It’s an enzyme that acts like a pair of DNA scissors. Guided by a specially designed RNA sequence, Cas9 can be directed to a specific location in the DNA sequence of an organism. Once there, it makes a precise cut in the DNA strand using PAM(Protospacer Adjacent Motif). This cut can disable a gene, or it can be used as an entry point to insert new genetic material.

The CRISPR-Cas9 system has been adapted by scientists for use in genetic engineering. The process begins with the design of a small piece of RNA with a short “guide” sequence. This guide RNA(crRNA part) is complementary to a specific target sequence in the organism’s DNA. When the CRISPR-Cas9 system is introduced into the cell, the guide RNA binds to the target DNA sequence. Cas9 then cuts the DNA at this precise location, guided by the PAM(Protospacer Adjacent Motif), a short DNA sequence that follows the targeted DNA sequence by the CRISPR system.

Once the DNA is cut, the cell’s natural repair mechanisms kick in. There are two main pathways for DNA repair: Non-Homologous End Joining (NHEJ) and Homology-Directed Repair (HDR). NHEJ often results in insertions or deletions at the cut site, which can disrupt the function of the gene – useful for gene knockout studies. HDR, on the other hand, allows for the introduction of specific DNA sequences at the cut site. This is how scientists can insert new genes or correct genetic mutations.

The potential applications of CRISPR-Cas9 are vast. In agriculture, for instance, it’s being used to create crops that are resistant to certain pests and environmental stresses, like drought. In medicine, CRISPR-Cas9 holds the promise of treating genetic disorders by correcting mutations at their source. For example, it has been used in experimental therapies for diseases like sickle cell anemia and cystic fibrosis.

The CRISPR-Cas9 system has revolutionized the field of genetic engineering. Its precision, ease of use, and versatility make it an invaluable tool for scientists across many disciplines.

I hope you’ve enjoyed this introduction to CRISPR-Cas9. Next time, we’ll delve into another exciting area of medicine. Until then, keep exploring and stay curious!