restriction enzymes

Overview of Restriction Enzymes

• Restriction enzymes are biological catalysts that cut DNA at specific sequences.

Interaction Between Viruses and Bacteria

• Virus Infection Process:

  • A virus attaches to a bacteria and injects its viral DNA.

  • The bacterial DNA is labeled for identification.

• Bacterial Defense Mechanism:

  • The bacteria methylates its own DNA using methylase to differentiate between its DNA and foreign DNA.

  • Methyl groups act as markers (purple dots) on bacterial DNA.

Role of Restriction Enzymes

• Function:

  • Floating restriction enzymes recognize unmethylated (foreign) DNA and cleave it.

• Process of Recognition:

  • Methylated (own) DNA is recognized and protected.

  • Unmethylated (foreign) DNA is destroyed for safety.

• Etymology:

  • Named "restriction enzymes" because they restrict viral growth by cutting viral DNA.

Palindromic Sequences

• Definition:

  • Palindromic sequences read the same forwards and backwards (e.g., GAA TTC).

• Importance in Restriction Enzymes:

  • These sequences are recognized by restriction enzymes (example: EcoR1).

Action of EcoR1

• Mechanism:

  • EcoR1 recognizes palindromic sequences and does not cut methylated DNA.

  • It cleaves unmethylated DNA strands at specific sites, resulting in sticky ends.

  • Example cleavage:

    • Original strands: GAA TTC and reverse: GAA TTC.

    • Cleavage results in two strands with sticky ends: AATTC and G.

Sticky Ends

• Definition:

  • The ends of DNA fragments that are left after a restriction enzyme has cut the DNA.

• Reannealing Potential:

  • Sticky ends can anneal (reattach) to other compatible DNA sequences.

Application in Biotechnology

• Human Insulin Production Example:

  • Bacterial DNA is cleaved using EcoR1.

  • An insulin gene is inserted into the bacterial DNA at the cleaved site by pairing sticky ends.

  • Resultant recombinant DNA in the bacteria produces human insulin, which can be harvested and purified for therapeutic use.

• Impact:

  • Provides a method to produce insulin quickly and economically for diabetic patients.