Lecture 30 - Genetic Engineering: Principles of Genetics

Genetic Engineering Overview and Key Discoveries

  • Foundational Knowledge: Lecture 30 of Principles of Genetics (BSCI 222), taught by Professor Thomas D. Kocher, focuses on Chapter 19 of the curriculum. Recommended practice problems include #33, 40, 42, 45, and 47.
  • Six Discoveries that Changed Genetics:     1. Restriction Enzymes: Bacterial defense mechanisms used to cut DNA at specific sites.     2. Southern Blot and DNA Hybridization: Techniques for identifying specific DNA sequences in a sample.     3. DNA Cloning: The process of making multiple copies of a DNA fragment using vectors.     4. DNA Sequencing: Methods to determine the exact order of nucleotides in a DNA molecule.     5. Polymerase Chain Reaction (PCR): A method for rapid amplification of specific DNA sequences.     6. CRISPR Gene Editing: A modernized and precise system for altering DNA sequences.

Restriction Enzymes (The "Molecular Scissors")

  • Origin and Function: Restriction enzymes are naturally produced by bacteria as a defense mechanism against invading viruses. They function by recognizing and cutting DNA at specific sequences.
  • Recognition Sites (Palindromes): Most restriction enzymes cut at palindromic sequences. In DNA, a palindrome exists when the complementary strands read the same in the 5′→3′5' \rightarrow 3' direction.     * Verbatim Metaphor: "A MAN, A PLAN, A CANAL, PANAMA" (a phrase that reads the same backward as forward).
  • Commonly used Restriction Enzymes:     * BamHI: Derived from Bacillus amyloliquefaciens. Recognition sequence: 5′−G∣GATCC−3′5'-G|GATCC-3' and 3′−CCTAG∣G−5′3'-CCTAG|G-5'. It produces cohesive (sticky) ends with a 3′3' overhang.     * EcoRI: Derived from Escherichia coli. Recognition sequence: 5′−G∣AATTC−3′5'-G|AATTC-3' and 3′−CTTAA∣G−5′3'-CTTAA|G-5'. It produces sticky ends.     * HaeIII: Derived from Haemophilus aegyptius. Recognition sequence: 5′−GG∣CC−3′5'-GG|CC-3' and 3′−CC∣GG−5′3'-CC|GG-5'. It produces blunt ends (cutting straight across both strands).     * HindIII: Derived from Haemophilus influenzae. Recognition sequence: 5′−A∣AGCTT−3′5'-A|AGCTT-3' and 3′−TTCGA∣A−5′3'-TTCGA|A-5'. It produces sticky ends.     * PvuII: Derived from Proteus vulgaris. Recognition sequence: 5′−CAG∣CTG−3′5'-CAG|CTG-3' and 3′−GTC∣GAC−5′3'-GTC|GAC-5'. It produces blunt ends.
  • Mechanism of Action:     1. The enzyme (often a dimer) binds to the specific recognition sequence.     2. It cleaves the sugar-phosphate backbone of the DNA.     3. If cutting with sticky ends, two different DNA molecules cut with the same enzyme will have complementary overhangs that can pair via hydrogen bonding.     4. DNA Ligase: This enzyme is required to seal the nicks in the sugar-phosphate backbone, creating a single recombinant DNA molecule.
  • Practical Tools: New England BioLabs provides an "Enzyme Finder" (v2.2.4) to help researchers locate commercially available enzymes by sequence, name, or overhang type.

Southern Blot and DNA Identification

  • Gel Electrophoresis:     * Principles: DNA molecules have a net negative charge and will migrate toward the positive electrode (anode) in an electric field.     * Matrix: An agarose gel serves as a porous matrix. Small DNA fragments move through the pores faster than large fragments.     * Reptation: The process by which DNA