Ch. 13

• Operon in bacteria: genes are clustered into units allowing the expression of related genes to be controlled as a unit
• Regulator gene codes for a repressor and is normally outside of the operon
• Promoter is where RNA polymerase initially binds
• Operator is where an active repressor binds preventing RNA polymerase from binding to the neighboring promoter
• Structural genes code for enzymes and proteins involved in the metabolic pathway of the operon
• Co-repressors activate an inactive repressor preventing RNA polymerase from binding to the promoter
• trp Operon is repressible and is turned off by the presence of tryptophan acting as a co-repressor
• lac Operon is inducible and is turned on by lactose acting as an inducer
• cAMP and CAP are involved in further control of the lac Operon
• Negative control involves an active/inactive repressor inhibiting transcription, while positive control facilitates transcription
• Eukaryotic cells have five main levels of control, with the first three in the nucleus and the last two in the cytoplasm
• Chromatin structure is governed by DNA methylation and histone acetylation
• Transcriptional control is the most critical level of control in eukaryotes
• Posttranscriptional control involves differential excision or inclusion of introns, splicing, and small RNA molecules
• Translational control occurs between mRNA leaving the nucleus and protein formation
• Posttranslational control ensures only functional proteins are active gene products
• Mutations are the primary source of genetic variation
• Causes of mutations include spontaneous errors, transposons, and exposure to mutagens
• Effect of mutations on protein activity can result in point mutations or frameshift mutations
• Mutations can cause cancer through a series of mutations involving genes like p53 and proto-oncogenes