Gene Regulation & Expression in Eukaryotes

Page 1

• Complexity of Gene Expression

  • Eukaryotic gene expression is more complex and regulated at multiple levels compared to prokaryotes.

Page 2

• Eukaryotic Genome Characteristics

  • Eukaryotic genomes are larger than prokaryotic genomes.

  • DNA organization allows specific segments to be accessed as needed.

  • DNA is wound around histone proteins, influencing accessibility.

  • Histones can move along the DNA, altering its structure based on signals.

Page 3

• Epigenetic Regulation

  • Histone Methylation

    • Causes coiling of DNA, making genes inaccessible and inactive.

  • Histone Acetylation

    • Opens up DNA, making genes accessible and active.

Page 4

• Epigenetic Changes

  • Alter nucleosome spacing and gene expression.

  • Influenced by development, environmental factors, drugs, aging, and diet.

  • Linked to diseases such as cancer, autoimmune disorders, mental disorders, and diabetes.

Page 5

• Regulation of Protein Synthesis at DNA Level

  • Gene regulation is influenced by internal and external signals.

  • Key components include:

    • Regulatory Genes: Code for regulatory proteins or RNA.

    • Transcription Factors: Regulatory proteins that interact with DNA.

    • Regulatory Sequences: DNA stretches that interact with regulatory proteins.

Page 6

• Eukaryotic Promoter Structure

  • Most promoters contain the TATA Box.

  • RNA polymerase requires transcription factors to bind to the promoter first.

  • Larger promoters allow more transcription factors to bind, enhancing control.

  • Eukaryotes have three RNA polymerases (I, II, III) for different genes.

Page 7

• Transcription Factors & Regulatory Sequences

  • Activator Proteins: Increase transcription speed by interacting with enhancers.

  • Repressor Proteins: Slow or block transcription by interacting with silencers or blocking transcription factors.

Page 8

• Activator and Repressor Dynamics

  • Gene expression depends on the presence of activators and absence of repressors.

  • Different combinations of activators and repressors lead to varied transcription levels.

Page 9

• Levels of Gene Regulation

  • Pre-transcriptional Level: Chromatin accessibility and transcription factors.

  • Post-transcriptional Level: RNA processing and stability.

  • Post-translational Level: Protein modifications and degradation.

Page 10

• Post-transcription Regulation

  • Allows rapid adjustment of gene expression in response to environmental changes.

  • Alternative Splicing: Produces different mRNAs from the same pre-RNA.

  • RNA Interference (RNAi): Small RNAs can degrade mRNA or block translation.

Page 11

• Variation in Gene Regulation

  • Within Similar Cells: Cells in a tissue can behave differently.

  • Between Different Cell Types: Different responses to the same signals.

  • Between Organisms: Gene regulation accounts for differences in organisms with similar genes.

Page 12

• Coordinating Gene Expression

  • Genes located far apart can be regulated together if they share transcription factors.

  • Transcription factors can lead to sequential gene expression.

Page 13

• Cell Differentiation

  • All cells are genetically identical, but only certain genes are active.

  • Different gene expression combinations lead to cell specialization.

Page 14

• Signaling and Development

  • Homeotic Genes: Control body segment formation and organ development.

  • Hox Genes: A type of homeotic gene that regulates body segmentation.

Page 15

• Hox Genes Structure

  • Contain a homeobox segment coding for a transcription factor.

  • Highly conserved across species, indicating a common evolutionary ancestor.

Page 16

• Mutations in Homeotic Genes

  • Hox genes are expressed in patterns that dictate body segment identity.

  • Mutations can lead to significant changes in body structure (e.g., fruit fly with two thoraxes).

Page 18

• Hox Genes in Vertebrates

  • Determine vertebrae types and numbers in animals.

  • Example: Hoxc-6 in chickens and snakes influences