molecular cloning

Molecular Cloning Overview

  • Definition of Molecular Cloning: Molecular cloning, also referred to as gene cloning or DNA cloning, involves taking DNA, inserting it into a new cell, and having that cell replicate itself and the inserted DNA.

  • Practical Example:

    • Involves using a plasmid from Agrobacterium tumefaciens (relevant terms to be discussed later) to insert a gene from a different organism into the plasmid.

    • The plasmid serves as a carrier molecule to introduce the gene into a new plant cell, resulting in a genetically engineered plant with potentially beneficial traits.

  • Real-World Application:

    • Example of fermentation produced chymosin in cheesemaking, created by inserting a cattle gene into microorganisms to produce chymosin protein.

Molecular Cloning Concepts

  • Recombinant Organisms: Molecular cloning creates recombinant organisms, where DNA is recombined into a new configuration. This also makes them transgenic organisms or genetically engineered organisms, as genes from one species are inserted into another.

  • Cloning Definition:

    • Cloning is the process of producing genetically identical copies of biological entities, whether they be organisms (like humans, cats, dogs) or microbes.

    • Natural Cloning Example: Identical twins resulting from one organism splitting into two.

Types of Cloning

  • Artificial Cloning: This is intentional cloning by humans. There are three types:

    1. Molecular Gene Cloning: Focus of the lecture.

    2. Reproductive Cloning: Creation of a whole new organism, typically in animals.

    3. Therapeutic Cloning: Similar to reproductive but focuses on obtaining stem cells from the products of a cloned embryo for therapeutic purposes.

  • Further Examples:

    • Gene cloning can also be employed to produce human insulin by inserting the insulin gene into bacteria to produce insulin as a therapeutic protein.

Key Techniques in Molecular Cloning

  • Restriction Enzymes: Enzymes used to cut DNA at specific sequences, allowing for DNA fragments from different sources to be joined together.

  • DNA Ligase: An enzyme that seals the nicks in the DNA backbone, permanently joining the DNA fragments together (like constructing a puzzle).

  • Plasmids:

    • Circular pieces of DNA capable of replicating independently of the organism's chromosomal DNA.

    • Need to be linearized to insert the target gene, resulting in a recombinant plasmid.

Cloning Procedure

  1. Digestion of DNA:

    • Both the plasmid and the gene of interest (e.g., insulin) are cut with restriction enzymes to create compatible ends for ligation.

  2. Ligation:

    • The cut plasmid and gene are combined; DNA ligase is used to seal them into a single recombinant plasmid.

  3. Transformation:

    • Introducing the recombinant plasmid into bacterial cells (competent cells) using:

      • Heat shock: Bacteria are subjected to a rapid temperature increase to facilitate DNA uptake.

      • Electroporation: Applying an electrical shock to help transform cells.

  4. Selection:

    • Using antibiotic selection to identify bacteria that have taken up the plasmid—only those with antibiotic resistance (pre-existing gene on plasmid) can survive on a plate containing the antibiotic.

  5. Confirmation:

    • Conclusively verifying that the plasmid contains the desired DNA insert and has no mutations, typically through PCR and DNA sequencing.

  6. Culturing Bacteria:

    • Bacterial colonies containing the plasmids are grown in liquid culture to produce numerous copies of the recombinant plasmid, serving as plasmid factories.

  7. Protein Production:

    • The bacteria are induced to express the genes inserted in the plasmid, enabling the production of proteins like insulin or chymosin.

    • This is known as heterologous protein production.

Applications of Molecular Cloning

  • Used in biotechnology for:

    • Producing therapeutic proteins, enzymes, hormones, etc.

    • Creating genetically modified organisms for agriculture, medicine, and research.

Research Focus and Further Study

  • Upcoming topics:

    • Methods for plasmid and gene preparation.

    • Investigation into the specific enzymes and tools used in the process (e.g., restriction enzymes, ligase).

    • Differences between expression and cloning hosts for gene expression in other organisms.

    • Manipulating transcription and translation to optimize protein production.

  • Activities: Engaging in practical exercises to familiarize with transforming and selecting bacteria with plasmids in various scenarios for hands-on learning.