Lecture Notes: Restriction Enzymes

Introduction to Restriction Enzymes

• Definition: Enzymes that cut DNA at specific sequences.
• Key Function: Protect bacteria from viral infections by destroying foreign DNA.

Example Scenario

• A bacteria is infected by a virus which injects viral DNA.
• Bacteria have their own DNA (bacterial DNA).
• Bacteria label their DNA with methyl groups (purple dots) via the enzyme methylase.

Role of Methylase

• Function: Methylates bacterial DNA to identify it as self.
• Purpose: Allows bacteria to distinguish between its own DNA and foreign (unmethylated) DNA from viruses.

Restriction Enzymes and Their Role

• Definition: Enzymes that recognize and cleave unmethylated viral DNA.
• They are present in the cytoplasm of bacteria and protect against viruses.
• Called "restriction enzymes" because they restrict viral growth.

Palindromic Sequences

• Definition: Sequences that read the same in both directions.
• Example Sequence: G-A-A-T-T-C (same forward and backward).
• Recognition by restriction enzymes.

Example of a Restriction Enzyme: EcoR1

• Function: Recognizes palindromic sequences and cleaves unmethylated DNA.
• Cleavage results in sticky ends (single-stranded overhangs).

Application in Biotechnology

Synthesis of Human Insulin

1. Extract Bacterial DNA: Obtain DNA from bacteria.
2. Cleavage: Use EcoR1 to cut bacterial DNA at a specific site.
3. Insert Human Insulin Gene:
   • Expose human insulin gene to EcoR1 to create compatible sticky ends.
   • Insert the insulin gene into the cleaved bacterial DNA.
4. Result: Bacteria can now synthesize human insulin.
5. Purification: Insulin can be purified for medical use.

Conclusion

• Restriction enzymes have significant applications in medicine and biotechnology, particularly in genetic engineering and drug production.