gene regulation

Regulation of Eukaryotic Gene Expression

Cell Specialization

  • Embryo Development

    • Embryos undergo division and differentiation.

    • Cells differentiate into various types by turning off unnecessary genes and only activating those essential for their specific function.

    • Turning genes on and off is fundamental for cell specialization.

Differential Gene Expression

  • Definition: The expression of different genes by cells that share the same genome.

Regulation of Chromatin Structure

  • DNA Packaging:

    • DNA is packaged with proteins called histones.

    • DNA wraps around histones to form nucleosomes, which clump together to create chromosomes.

  • Types of Chromatin:

    • Heterochromatin: Highly condensed form of DNA.

  • Epigenetic Mechanisms:

    • Acetylation: Adding an acetyl group to histones, loosening DNA and exposing promoters for transcription.

    • Methylation: Adding a methyl group, reinforcing histone packing and keeping DNA tightly bound.

  • Inheritance Patterns:

    • Patterns of methylation and acetylation can be inherited, affecting gene expression across generations.

    • Epigenetic Inheritance: Transmission of traits through mechanisms that do not directly involve DNA sequence changes.

Organization of a Typical Eukaryotic Gene

  • Gene Structure:

    • Sequences exist upstream of the gene and promoter that can bind to transcription factors.

    • Activator Proteins: Bind to enhancer sequences to promote gene expression.

    • Transcription Factors: Bind to the TATA box.

Mechanisms of Transcription and Regulation

Role of Activators and Repressors

  • Gene Activation:

    • Activators bring DNA loops to facilitate the binding of RNA polymerase necessary for transcription.

    • If activators are not present, the gene remains inactive (off).

  • Repressor Proteins:

    • Some transcription factors can act as repressors, preventing gene expression.

  • Cell Differentiation:

    • Depends significantly on the presence and type of activators available, leading to the formation of the appropriate cell types.

Post-Transcriptional Regulation

  • Alternative RNA Splicing:

    • Regulates gene expression by determining which exons are included in mRNA.

  • mRNA Degradation:

    • Controls the lifespan of mRNA molecules, which affects their translation frequency.

    • Protects the poly-A tail to enhance stability during this process.

Protein Processing and Degradation

  • Protein Lifespan:

    • Proteins may either be used once and degraded or reused multiple times.

  • Ubiquitin System:

    • Ubiquitin tags proteins for degradation, playing a crucial role in regulating protein quantities within the cell.