Chapter 18

• What can activate genes?

  Inducer molecules
• What can inhibit gene activation?

  Repressor proteins
• What is a regulatory gene?

  A DNA sequence coding for regulatory proteins
• How do operons regulate gene expression?

  • Operons consist of genes regulated together.
  • Repressible operons are inhibited by repressors.
  • Inducible operons are activated by inducers.
• What is positive control in gene expression?

  Activation of gene expression by activators
• What is negative control in gene expression?

  Inhibition of gene expression by repressors
• How does DNA methylation affect gene expression?

  It typically represses gene expression
• How does histone acetylation affect gene expression?

  It typically enhances gene expression
• How is timing and coordination regulated in normal development?

  • Through specific gene expression events.
  • Involves pattern formation.
  • Involves induction processes.
• What is the role of gene regulation in embryonic development and cancer?

  • Essential for proper embryonic development.
  • Misregulation can lead to cancer.
• What is the role of miRNAs in cellular functions?

  They regulate gene expression post-transcriptionally
• What is required for the process of transcription?

  RNA polymerase and the promoter
• The initiation stage of translation brings together mRNA, a tRNA bearing the first amino acid of the polypeptide, and the two subunits of a ribosome.
• Cells can adjust the activity of enzymes already present. This is a fairly rapid physiological response, which relies on the sensitivity of many enzymes to chemical cues that increase or decrease their catalytic activity
• Cells can adjust the production level of certain enzymes via a genetic mechanism; that is, they can regulate the expression of the genes encoding the enzymes.
• Operon

  cluster of related genes with on/off switch found in prokaryotes.
• What are the three parts of the Operon?

  • Promoter - where RNA polymerase attaches
  • Operator - “on/off switch”, controls access of RNA polymerase
  • Genes - code for related enzymes in a pathway
• Regulatory Gene

  produces repressor protein that binds to operator to block RNA polymerase
• A promoter is a site where RNA polymerase can bind to DNA and begin transcription
• Repressor

  A protein that inhibits gene transcription
• Transcription is the synthesis of RNA using information in DNA

  DNA → RNA
• Translation is the synthesis of a polypeptide using the information in mRNA
• DNA codes mRNA to make proteins
• RNA polymerase synthesizes RNA molecules through transcription from the template of DNA
• What direction is RNA synthesized?

  5' to 3' direction
• Operator

  A sequence of nucleotides near the start of an operon to which an active repressor can attach
• Inducer

  A specific small molecule that binds to a bacterial repressor protein and changes the repressor's shape so that it cannot bind to an operator, thus switching an operon on
• Corepressor

  A small molecule that binds to a bacterial repressor protein and changes the protein's shape, allowing it to bind to the operator and switch an operon off
• Tryptophan is an amino acid produced by an anabolic pathway catalyzed by three enzymes
• The trp operon can be switched off by a protein that is called the trp repressor
• The trp repressor, like most regulatory proteins, is an allosteric protein, with two alternative shapes: active and inactive
• The trp repressor is synthesized in the inactive form
• What type of operon is the trp operon?

  Repressible operon
• Post translational control refers to regulation of gene expression after translation
• In prokaryotes, control of gene expression usually occurs at the transcriptional control level
• Prokaryotes must survive in environments that constantly change in the availability of nutrients
• Prokaryotes commonly control expression of genes using operons
• Operon

  A set/group of prokaryotic genes of related function controlled by a single promoter
• Transcription of the operon is regulated by the operator
• an operator is a region of DNA where regulatory proteins bind