BIS 2A Lecture Notes - Lac Operon, Operon, Catabolite Activator Protein
Gene Regulation
• Gene regulation: controlling when and how much a gene is expressed in response to
cellular and environmental conditions
o Gene expression: determined by the number of functional end products
produced (RNA or protein)
▪ Regulation of gene expression can also affect the functional state, form,
and stability of the gene product
o Gene regulation can occur at any step from transcription, translation, and
degradation of the biomolecules involved
▪ Regulation of transcription through regulation of binding of RNA
polymerase
• Activation and repression of transcription
o Transcription factor proteins (or sigma proteins in bacteria) bind to RNA
polymerase and influence binding of RNA polymerase to the promoter
o Promoters have different strengths
▪ Constitutive: active promoter without any form of regulation
• Strong promoters produce higher number of transcripts
• Weak promoters produce lower number of transcripts, can save
energy and resources when high concentrations are not needed
o Changing nucleotide sequence of promoter can change
promoter strength
▪ Activated/induced: external stimulus increases or turns on transcription
▪ Repressed: external stimulus decreases or turns off transcription
o Different types of transcription factors
▪ Bind to DNA sequences known as operators, which are usually close to
the promoters
• Activators increase transcription while repressors decrease
transcription
• Certain transcription factors serve as activators in some
conditions and repressors in others
o Allosteric regulation of transcription factors through small molecules
▪ Small molecules are called inducers or co-activators or co-repressors
• Usually food or metabolites that allow responses to
environmental conditions
▪ Bind to allosteric sites through hydrogen and ionic bonds
• Causes conformational change that either causes release from
DNA (increasing transcription) or binding to DNA (decreasing
transcription)
▪ Regulation depends on concentration of small molecules and
transcription factors, pH (protonation and deprotonation)
• Higher concentrations of small molecules and transcription
factors leads to greater regulation of the gene
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