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Control mechanisms. 5.5. Controlling Transcription and Translation of Genes. Housekeeping Genes : needed at all times: needed for life functions vital to an organism. Constantly transcribed and translated. not all proteins are needed at all times
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Controlling Transcription and Translation of Genes • Housekeeping Genes: needed at all times: needed for life functions vital to an organism. • Constantly transcribed and translated. • not all proteins are needed at all times • Ex// insulin only need when glucose levels are high • Transcription factors: proteins that switch on genes by binding to DNA and helping the RNA polymerase to bind. • Gene Regulation: turning on or off specific genes depending on requirements of organism. • Vital to survival.
Operons Operon: cluster of genes under control of a promoter and operator (prokaryotic). Acts as a simple regulatory loop.
Repressor Protein: regulatory molecule that binds to an operator site and prevents the transcription of an operon.
Two Major Operons (in E. Coli) • lacoperon • Required for transport and metabolism of lactose • trpoperon • Codes for the production of tryptophan an amino acid.
lacoperon (1) • Lactose: ____________ + ______________ • E. Coli bacteria found in mammalian intestines can use energy from lactose for growth. • β-galactosidase: enzyme that catalyzes lactose. • When lactose not available, B-g is not made. • When would B-g cease on being produced by E. Coli in a mammalian intestine? ______________________________________________
lacoperon (2) • Consists of three genes: • lacZ: gene for the enzyme β-g. • LacY: gene for β-g Permease: allows lactose to be permeable to cell membrane. • lacA: unknown function.
lacoperon: If Lactose not Present • Lacl protein: repressor protein of lactose metabolism • Binds to the lacoperon operator, preventing RNA polymerase from transcribing the lacoperon genes. • Operon and operator actually overlap, so RNA poly cannot bind to DNA.
lacoperon: If lactose IS present • If lactose present, lacl must be removed from operator so lacoperon genes can be transcribed. • Lactose: known as an ‘inducer.’ Binds to LacI protein change conformation of LacI cannot stay bound to operator region no more block!
trpoperon(1) • Tryptophan: an _______________ used by E.Coli to make ________________. • E. Coli in inside of mammalian intestine can absorb trp from diet. If no host, needs to produce trp. • 5 genes responsible in the metabolic pathway of the trpoperon.
Trpoperon: when trp is not present • Inactive repressor is not blocking operator. • RNA polymerase can transcribe operon.
Trpoperon: when trp is present • Tryptophan acts as a corepresser: binds to the repressor protein conformation change can bind to the operator block transcription. (NO NEED FOR ENZYMES THAT MAKE TRP WHEN TRP IS ALREADY PRESENT!)
Seatwork/Homework • Page258, #1-6.