Restriction Enzymes

Introduction to Restriction Enzymes

• Definition: Enzymes that cut DNA at specific sequences.
• Role: Protect bacteria from viruses by destroying foreign DNA.

Example Scenario

Virus Infection of Bacteria

• Virus injects viral DNA into bacteria.
• Bacteria has its own DNA.
• Viral DNA (non-methylated) vs. bacterial DNA (methylated with purple dots).

Methylation Process

• Methyl groups: Purple dots on bacterial DNA.
• Methylase: Enzyme that methylates bacterial DNA.
• Methylation allows bacteria to distinguish its own DNA from foreign DNA.

Action of Restriction Enzymes

• Recognize and leave methylated bacterial DNA intact.
• Identify and cleave unmethylated foreign DNA.
• Named restriction enzymes because they restrict viral growth.

Palindromic Sequences

• Defined as sequences that are the same when read 5’ to 3’ on one strand and 3’ to 5’ on the complementary strand.
• Example: G-A-A-T-T-C.
• Palindromic sequences are recognized by restriction enzymes.

EcoR1 Restriction Enzyme

• Recognizes the palindromic sequence GAATTC.
• Cleaves DNA at the site, creating sticky ends.
• Sticky Ends: Overhanging sequences that can re-anneal.

Application: Synthesis of Human Insulin

• **Process: Extract and cleave bacterial DNA using EcoR1;
  • Insert human insulin gene with complementary sticky ends.
  • Re-anneal to combine bacterial DNA with insulin gene.
• Result: Bacteria synthesize human insulin.
• Outcome: Mass production of insulin for diabetic patients.

Summary

• Restriction enzymes are crucial in biotechnology and pharmaceuticals for gene manipulation and therapy.