chapter 15

• What is the main way bacteria respond to environmental changes?

  By regulating transcription
• Why have bacteria evolved to produce only necessary products?

  Natural selection favored this efficiency
• How can a prokaryotic cell regulate enzyme production?

  Through feedback inhibition or gene regulation
• What model controls gene expression in bacteria?

  The operon model

  
• What is an operon?

  • A group of functionally related genes
  • Controlled by a single on-off switch
  • Includes operator, promoter, and controlled genes

  
• What is the role of the operator in an operon?

  It acts as a regulatory switch

  
• How can an operon be switched off?

  By a protein repressor binding to the operator

  
• What does a repressor do in gene transcription?

  It blocks RNA polymerase

  
• What determines the activity of a repressor?

  The presence of other molecules
• What is a corepressor?

  A molecule that helps a repressor switch off an operon
• What is the default state of the trp operon?

  It is on and transcribes genes

  
• What happens when tryptophan is present in relation to the trp operon?

  Tryptophan binds to the repressor, turning the operon off

  
• What are the two types of negative gene regulation in operons?

  • Repressible operon: usually on, repressor shuts off transcription
  • Inducible operon: usually off, inducer activates transcription

  
• What is the lac operon responsible for?

  Hydrolysis and metabolism of lactose

  
• What is the state of the lac repressor when lactose is absent?

  It is active and switches the lac operon off

  
• What role does allolactose play in the lac operon?

  It inactivates the repressor to turn on the operon

  
• What happens to the lac operon when lactose is present?

  The repressor becomes inactive, allowing transcription

  
• What type of pathways do inducible enzymes typically function in?

  Catabolic pathways
• What type of pathways do repressible enzymes typically function in?

  Anabolic pathways
• How does gene regulation differ between prokaryotes and eukaryotes?

  • Prokaryotes: primarily at transcription
  • Eukaryotes: at multiple stages including transcription, RNA processing, and translation

  
• What is differential gene expression?

  Expression of different genes in identical cells
• What can errors in gene expression lead to?

  Imbalances and diseases like cancer
• What stages can gene expression be regulated in eukaryotic cells?

  1. Chromatin modification
  2. RNA processing
  3. Translation
  4. Protein processing
  5. Degradation of mRNA and proteins

  
• What is the role of chromatin in gene expression?

  It regulates accessibility of DNA for transcription

  
• What are histones?

  Proteins that pack DNA in chromatin

  
• What is euchromatin?

  Loosely packed chromatin accessible for transcription

  
• What is heterochromatin?

  Tightly packed chromatin that is less accessible

  
• How do histone modifications affect gene expression?

  They can loosen or tighten chromatin structure

  
• What is the effect of DNA methylation on transcription?

  It is associated with reduced transcription
• How does chromatin modification influence gene expression?

  It alters the ability to bind transcription machinery

  
• What is the significance of the cell cycle on chromatin structure?

  Chromatin packing changes during the cell cycle
• What happens to chromatin during interphase?

  Most chromatin is loosely packed

  
• What is the role of histone acetylation?

  It loosens chromatin structure for transcription

  
• What is the effect of adding methyl groups to DNA?

  It can lead to long-term gene inactivation

  
• How does the regulation of transcription initiation occur?

  Through chromatin modification affecting transcription machinery binding

  
• What is the relationship between gene expression and cellular function?

  Gene expression determines cellular function and specialization
• What effect does acetylation have on chromatin structure?

  It loosens chromatin structure

  
• How does acetylation promote transcription?

  By loosening chromatin structure

  
• What is DNA methylation?

  Addition of methyl groups to DNA
• What is the effect of DNA methylation on transcription?

  It is associated with reduced transcription