Biotechnology

Recombinant DNA Technology - Genetic Engineering

  • Definition and Purpose:

    • Genetic engineering is the purposeful manipulation of genetic material, which extends selective breeding in animals and plants.

  • Requirements:

    1. Manipulation of DNA in vitro: This refers to working with DNA outside of cells.
    2. Gene Insertion: Involves inserting genes from one organism (e.g., humans) into plasmids or other vectors (self-replicating DNA).
    3. Cloning: Producing genetically identical progeny (e.g. by growing the recombinant DNA in bacteria).

  • Benefits:

    • Allows for large-scale production of recombinant DNA, enabling further study (e.g., sequencing) and production of the encoded proteins, contributing to biotechnology and pharmaceutical production.

Tools of Recombinant DNA Technology

  1. Restriction Enzymes:

    • Endonucleases that cut DNA at specific palindromic sequences, resulting in specific DNA fragments.
    • Named based on the genus initial and specific epithet (example: EcoRI originates from E. coli).

  2. Vectors:

    • DNA molecules used to deliver genes into cells.
    • Characteristics include survival in host cells, ability to replicate independently, and markers (e.g. AmpR) to confirm gene insertion.
    • Common vectors: Plasmids, Charon (λ) phages.

  3. DNA Ligase:

    • Enzyme that joins DNA fragments to form recombinant DNA, functioning in the following process:
    1. Isolate plasmid and gene of interest DNA.
    2. Cut both DNAs with the same restriction enzyme and mix fragments with DNA ligase.
    3. Transform competent E. coli cells with ligated DNA.
    4. Grow on selective medium to isolate recombinant bacteria which contain the desired plasmid.
    5. Isolate and purify target proteins, leading to the production of desired products.

Techniques and Applications of Recombinant DNA Technology

  1. Gene Libraries:

    • A collection of cloned DNA fragments that represent all genes of a particular organism.
    • Screening methods include observing protein production or using DNA probes (labeled fragments complementary to genes of interest).

  2. Gel Electrophoresis:

    • Technique for separating DNA fragments based on size using an electrical current through a gel matrix.
    • Results in a "smear" from genomic digestion, which requires further processes to locate specific fragments.

  3. Southern Blotting:

    • A method for transferring DNA fragments from a gel to a membrane.
    • Involves hybridization with radioactive probes, allowing visualization of specific bands reflective of alleles and RFLPs (restriction fragment length polymorphisms).
    • Useful in forensic analysis of DNA.

  4. Polymerase Chain Reaction (PCR):

    • Technique for amplifying small DNA amounts.
    • Steps include denaturation (heating to separate strands), priming (using primers), and extension (synthesizing new DNA using Taq polymerase). Used in various applications including forensics and diagnostics.

  5. Inserting DNA into Cells:

    • Methods include:
      • Electroporation: Electrical current makes holes in cell walls to facilitate DNA entry.
      • Protoplast Fusion: Merging plant cells to share genetic material.
      • Injection Techniques: Using gene guns or microinjection for direct DNA insertion.

  6. Nucleotide Sequencing:

    • DNA sequencing involves utilizing fluorescently-labeled nucleotides to create fragments for analysis, revealing the genetic information.

  7. Microarrays:

    • A technique with spots of DNA on a chip used to study gene expression.
    • Involves isolating mRNA, synthesizing cDNA from it, labeling, hybridizing to the chip, and scanning for expression levels.

  8. CRISPR Technology:

    • CRISPR utilizes the Cas9 protein guided by RNA to target and manipulate specific genes, allowing for gene inactivation.

Risks and Benefits of Recombinant DNA Technology

  • Historical Context:

    • A moratorium on certain recombinant DNA experiments was established in 1974 and lifted in 1981 due to:
    1. Lack of illness linked to recombinant work in labs.
    2. Non-infectious E. coli strains used in research even at high doses.
    3. Observations showing recombinant E. coli were outcompeted in nature.
    4. Standard control measures effectively managed recombinant strains.

  • Modern Concerns:

    • Risks include potential bioterrorism with genetically-modified pathogens and ethical dilemmas surrounding genetic manipulation (e.g., genetic databases, 'designer babies').