🔍 What is CRISPR?
CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) is a natural immune system found in bacteria.
It protects them from viruses by storing pieces of viral DNA, so they can recognize and destroy it next time.
Scientists adapted this system into a powerful gene-editing tool, most commonly using the CRISPR-Cas9 system, to precisely cut DNA at targeted sites.
It’s like having molecular scissors guided by a GPS.
✂️ How does CRISPR-Cas9 work?
1️⃣ Design a guide RNA (gRNA)
- This RNA is complementary to the DNA sequence you want to cut.
2️⃣ Cas9 enzyme binds to gRNA
- The gRNA takes Cas9 to the exact spot on the genome.
3️⃣ Cas9 makes a cut (double-strand break)
- The cell tries to repair the break:
- Either introduces errors (knockout genes) or allows inserting new genes (knock-in).
🔄 Mini flowchart: CRISPR editing workflow
Target gene identified
↓
Design guide RNA (gRNA)
↓
Load gRNA + Cas9 into cells
↓
Cas9 cuts DNA at target site
↓
DNA repair ➔ edits the genome
🌱 Applications in microbes, plants, humans
| Field | Applications |
|---|---|
| Microbes | Engineer bacteria to produce more enzymes, or remove antibiotic resistance genes. |
| Plants | Create drought-resistant or disease-resistant crops by knocking out susceptibility genes. |
| Humans | Research on fixing mutations causing diseases like sickle cell anemia, certain forms of blindness. |
🧑💻 Bioinformatics tools to design guide RNAs
Before doing CRISPR in the lab, you use computational tools to design gRNAs that:
✅ Precisely match your target DNA
✅ Avoid off-target sites (which could cause unwanted cuts)
Popular tools include:
| Tool | What it does |
|---|---|
| Benchling | Easy design of gRNAs with off-target scoring. |
| CRISPOR | Designs guides and checks for off-targets. |
| CHOPCHOP | Designs & evaluates guide RNAs for many organisms. |
📝 Mini case study: fixing a mutation in sickle cell anemia
🔬 Scenario
Sickle cell anemia is caused by a single mutation in the HBB gene.
🧬 Using CRISPR
- Scientists design a guide RNA targeting the HBB mutation.
- Cas9 cuts the DNA near the mutation site.
- The cell’s repair machinery, guided by a template DNA, corrects the mutation.
🚀 Why important?
This offers hope to permanently fix genetic diseases at their root cause.
✅ Short summary table
| What? | Why important? |
|---|---|
| CRISPR-Cas9 | Precise, cost-effective, easy-to-use gene editing. |
| Guide RNA design | Ensures cuts happen only at desired location. |
| Applications | Crop improvement, treating genetic diseases, creating industrial microbes. |