Gene Expression & Epigenetics

Review of Key Concepts

• Protein Synthesis: Process from DNA to proteins (Transcription and Translation)
  • Transcription: DNA to RNA (RNA polymerase)
  • Translation: RNA to protein (ribosomes)

Basics of Gene Expression

• Controls the transcription and translation of genes (turning genes on/off)
• Occurs in both prokaryotes and eukaryotes
• Reflects how organisms respond to their environment and differentiate into cell types

Gene Expression in Prokaryotes

Overview

• Efficiency: Key for survival and response to environment
• Gene regulation: Controlled via operons (on/off switches in DNA)

Operons

• Operons consist of:
  1. Promoter: Recruits RNA polymerase
  2. Operator: On/off switch
  3. Structural Genes: Encode proteins
  4. Regulator Gene: Produces a repressor protein

Example: Trp Operon (Repressible)

• Tryptophan synthesis
• Components:
  • Promoter recruits RNA polymerase
  • Operator is unblocked initially, allowing transcription
  • Structural genes encode enzymes for tryptophan production
  • Regulatory gene produces an inactive repressor
• Excess tryptophan binds to repressor, activating it, and repressing operon

Inducible Operons

• Lac Operon: Breaks down lactose
• Typical state: Repressor bound, operon off
• Lactose presence: Binds to repressor, making it inactive, operon turns on

Gene Expression in Eukaryotes

Differences from Prokaryotes

• More complex gene regulation mechanisms
• Adjust cell types and functions differently based on environment

Key Concepts

• Positive Regulation: Genes are generally off unless activated by transcription factors
• Transcription Factors: Essential for RNA polymerase recruitment to promoters
• No Operons in Eukaryotes: Single-gene regulation
• Alternative Splicing: Produces different proteins from one gene by removing introns
• Additional Controls: mRNA degradation, protein modification post-translation

Levels of Regulation

• Transcription: Initiation requires transcription factors
• RNA Processing: Alternative splicing, mRNA modifications (cap and tail addition)
• Translation: Enzymes in the cytoplasm can degrade mRNA
• Post-Translation: Proteins can be modified or degraded

Epigenetics

Overview

• Heritable changes in gene expression outside DNA sequence
• Affects physical characteristics and potential susceptibility to diseases

Mechanism

• Chromatin Structure: DNA packing affects gene access
• Methylation: Addition of methyl groups to DNA
  • More methylation = more packing = gene off
  • Less methylation = less packing = gene on

Example Studies

• Identical Twins: Differences in gene expression over time due to environmental effects
• Animal Studies: Licking in mice affects stress responses across generations
• Impacts of Environment: Food availability, abuse, substance exposure can influence gene expression

Takeaway

• Importance of Epigenetics: Understanding complex inheritance and gene regulation
• Future Studies: Greater exploration in genetics, psychological impacts, and potential applications in medicine and biology