Gene Expression in Prokaryotes and Eukaryotes

• Why do cells in a multicellular organism look and function differently?

  Due to selective gene expression
• What determines the phenotype of a cell or organism?

  The combination and levels of expressed genes
• What results from the expression of genes for tissue-specific proteins?

  Observable cell differentiation
• What do all cells in a multicellular organism contain?

  The same DNA
• What does gene regulation influence in a cell?

  The products/proteins a cell produces
• What are operons in prokaryotes?

  Groups of genes that are coordinately regulated

  
• What are the parts of an operon?

  Promoter, operator, structural genes, regulatory genes

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

  It is where RNA polymerase binds to initiate transcription

  
• What do structural genes in an operon code for?

  Proteins/enzymes of the operon
• What do repressor proteins do in an operon?

  They prevent transcription and expression of structural genes

  
• What is the function of an operon?

  A functional unit of transcription and gene regulation

  
• What must happen for a gene in an operon to be expressed?

  It must be transcribed and translated

  
• What characterizes inducible operons?

  Structural genes are usually not expressed
• What does the operator do in an operon?

  It serves as the site of repressor binding

  
• What do regulatory genes in an operon code for?

  Repressor proteins

  
• How are operons classified?

  As inducible or repressible

  
• What is a commonly cited example of an inducible operon?

  The lac operon
• What happens to repressor proteins in inducible operons under certain conditions?

  Inducers bind to them, causing them to unbind from the operator
• What do the structural genes in the lac operon code for?

  Enzymes that break down lactose
• Why do bacterial cells not express the structural genes of the lac operon when lactose is absent?

  It makes no sense to manufacture lactase

  
• What happens when bacterial cells have access to lactose?

  Lactose acts as an inducer, allowing gene expression

  
• What do repressor proteins do once all lactose is used up?

  They bind to the operator and cease gene expression

  
• How do operons function in prokaryotes?

  Like negative feedback loops to save energy

  
• What characterizes repressible operons?

  Structural genes are usually expressed

  
• What happens when a corepressor binds to a repressor protein in repressible operons?

  The repressor can bind to the operator and block transcription

  
• What is a commonly cited example of a repressible operon?

  The trp operon
• What do the structural genes in the trp operon code for?

  Enzymes that make the amino acid tryptophan
• Why do bacteria stop making enzymes to produce tryptophan when exposed to high levels of tryptophan?

  It doesn't make sense to manufacture it
• What happens when environmental tryptophan is used up?

  The repressor unbinds and genes are expressed again
• How does gene regulation in eukaryotic cells differ from prokaryotic cells?

  It is controlled on several different levels
• What is chromatin structure in eukaryotic cells associated with?

  Proteins known as histones
• How does the degree of DNA compaction affect gene expression?

  It affects accessibility to RNA polymerase
• What are active genes referred to as?

  Euchromatin
• What are inactive genes referred to as?

  Heterochromatin
• What happens when methyl groups are attached to cytosines of a gene?

  DNA becomes tightly wound and inactive
• What effect do acetyl groups have on histone proteins?

  They cause DNA to uncoil and be expressed

  
• What is acetylation?

  The process of adding acetyl groups
• How do epigenetic changes affect gene expression?

  Through reversible modifications of DNA or histones

  
• What does epigenetics refer to?

  Changes in gene expression not based on sequence
• How can epigenetic changes occur in identical twins?

  Due to different lifestyles and environments