Restriction Enzymes Lecture

Introduction to Restriction Enzymes

• Definition: Restriction enzymes are proteins that bacteria use to protect themselves against viral infections by cutting foreign DNA.
• Function: Recognize specific DNA sequences and cut them, preventing viral replication.

Bacteria and Viral Infection

• Scenario: Virus infects bacteria by injecting viral DNA.
• Bacterial Defense:
  • Bacteria protect themselves by methylating their own DNA with methyl groups (purple dots).
  • Methylase Enzyme: Adds methyl groups to the bacterial DNA, distinguishing it from foreign DNA.

Role of Restriction Enzymes

• Recognition: Restriction enzymes float in the bacterial cytoplasm, distinguishing between methylated (self) and unmethylated (foreign) DNA.
• Process: When they encounter unmethylated DNA, they cut it, preventing virus replication.
• Origin of Name: Named because they restrict or limit viral growth.

Mechanism of Action

• Specific Sequences:

  • Restriction enzymes recognize specific palindromic DNA sequences (e.g., G-A-A-T-T-C).
  • Palindromic Sequence: Reads the same forward and backward on complementary strands.

• Example: EcoR1 Enzyme:

  • Recognizes the sequence G-A-A-T-T-C.
  • Cuts unmethylated DNA and creates two DNA fragments with sticky ends.
  • Sticky Ends: Overhanging sequences that can reanneal or attach to other complementary DNA sequences.

Applications of Restriction Enzymes

Genetic Engineering

• Synthesis of Human Insulin:
  • Cut bacterial DNA with EcoR1, creating sticky ends.
  • Insert human insulin gene, pre-exposed to EcoR1 to have compatible sticky ends.
  • Result: Bacteria synthesize human insulin, which can be purified for medical use.

Biotechnology

• Insulin Production:
  • Economical and rapid production of insulin for diabetic patients.

Summary

• Restriction enzymes are crucial in biotechnology and pharmaceuticals for their ability to manipulate and insert foreign genes into host genomes, enabling the production of important proteins like insulin.