2024-2024-REGULATION OF GENE EXPRESSION-KIM

1. Gene Expression

  • Definition: Conversion of genetic information into mRNA (transcription) and then into functional proteins (translation).

  • Regulation occurs at various stages:

    • RNA transcription initiation.

    • RNA processing.

    • Post-translational modification of proteins.

2. Gene Regulation

  • Definition: Process used by cells to increase or decrease the production of specific gene products (proteins or RNA).

  • Importance:

    • Controls cell structure and function.

    • Enables cellular differentiation and morphogenesis.

    • Ensures versatility and adaptability of organisms.

  • Misregulation can lead to:

    • Cancer.

    • Developmental abnormalities.

3. Gene Expression Patterns

  • Housekeeping Genes: Expressed in all cells at all times for routine metabolic functions (e.g., respiration).

  • Differentiation-Specific Genes: Expressed only in certain cell types (e.g., antibody production in plasma cells).

  • Condition-Specific Genes: Activated or repressed in response to external or internal conditions (e.g., hormone-induced gene activation).

4. Types of Genes

  1. Constitutive Genes:

    • Always expressed.

    • Responsible for producing proteins required constantly (e.g., glycolysis enzymes).

  2. Regulated Genes:

    • Expression changes under specific conditions.

    • Inducible: Increase mRNA/protein levels.

    • Repressible: Decrease mRNA/protein levels.

5. Regulation of Transcription

  • Involves regulatory sequences and molecules:

    • Cis-acting elements: Regulatory sequences located on the same chromosome (e.g., promoters, enhancers).

    • Trans-acting molecules: Proteins or factors from a different chromosome that regulate gene expression.

  • Promoters: Initiation sites for transcription.

  • Enhancers: Increase transcription levels, even when located far from the start site.

  • Repressors/Silencers: Decrease transcription levels by blocking RNA polymerase or transcription factors.

6. Regulation in Eukaryotes

  • Can occur at multiple levels:

    • Transcription: Interaction of transcription factors, promoters, and enhancers.

    • Post-Transcription: Alternative splicing, mRNA stability, translational control.

    • Protein Modification: Modulation of stability, activation, and targeting.

    • Chromatin Remodeling: Unpacking of DNA for transcription (euchromatin).

7. Regulation in Prokaryotes

  • Gene regulation often involves operons:

    • Lac Operon: Activated when lactose is present and glucose is absent.

    • Trp Operon: Repressible operon that synthesizes tryptophan only when needed.