Control of Gene Expression Notes

Chapter 11 - Control of Gene Expression

Introduction to Gene Cloning

  • Cloning Defined: Cloning is the process of creating an individual that is genetically identical to a single parent, known as a clone. Example: Dolly the Sheep.

Types of Cloning

  • Reproductive Cloning: Involves producing a genetically identical organism.
    • Somatic Cell Nuclear Transfer (SCNT):
    • Process of taking a nucleus from a somatic (body) cell of an adult donor and inserting it into an egg cell from which the nucleus has been removed.
    • Steps in SCNT:
      1. Remove the nucleus from the egg cell.
      2. Insert the nucleus from the donor cell into the egg cell.
      3. Grow the cell in culture to produce a ball of cells (embryo).
      4. Implant the embryo into a surrogate mother.
      5. Clone of the donor is born.
  • Therapeutic Cloning: Focused on the extraction and use of embryonic stem cells for medical therapies.
    • Steps:
    1. Remove stem cells from an embryo.
    2. Grow these stem cells in culture.
    3. Induce stem cells to develop into specialized cells for therapeutic applications (e.g., nerve cells, heart cells).

Gene Regulation in Prokaryotic Cells

  • Overview: Gene regulation controls the transcription of genes in prokaryotic cells, such as E. coli.
    • Key Components:
    • Regulatory gene: Codes for a repressor protein.
    • Operator: A segment of DNA that repressor binds to.
    • Promoter: A DNA sequence where RNA polymerase binds to initiate transcription.
    • Operon Functionality (Example: Lactose Operon):
    • Inactive Repressor: Lactose present inactivates the repressor, allowing RNA polymerase to bind to the promoter and activate the operon for the production of lactose enzymes.
    • Active Repressor: In absence of lactose, the repressor binds to the operator, preventing transcription.

Gene Regulation in Eukaryotic Cells

  • Cell Differentiation: Eukaryotic cells differentiate into various cell types (muscle, skin, brain, blood), despite having the same genetic material.
  • Gene Regulation Mechanisms:
    • DNA Packing: Eukaryotic DNA is tightly packed with histones forming nucleosomes, impacting gene availability for transcription.
    • DNA structures from 2 nm (double helix) to 700 nm (metaphase chromosome).
    • Regulatory Proteins:
    • Enhancers and transcription factors help activate gene expression.
    • DNA bending allows interaction between enhancers and promoters, facilitating transcription.
  • X Chromosome Inactivation:
    • Barr Bodies: In females, one X chromosome is randomly inactivated, leading to observable patterns (e.g., calico cats).

Master and Homeotic Genes

  • Master Genes: Control the expression of other genes, influencing large developmental processes.
  • Homeotic Genes: Type of master gene guiding the formation and arrangement of body structures.

Applications of Cloning

  • Potential applications in livestock improvements, conservation efforts, and research environments.

Therapeutic Cloning and Stem Cells

  • Stem Cell Overview:
    • Types:
    • Adult Stem Cells: Found in bone marrow, capable of differentiating into specific cell types.
    • Embryonic Stem Cells: Cultured for yielding multiple differentiated cell types (e.g., blood cells, nerve cells, heart muscle cells).
  • Applications: Development of therapies for various conditions using differentiated cells from stem cells.