CONTROL MECHANISMS5.5
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 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.
Control of Gene Expression in Eukaryotic Cells
OperonsOperon: 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) lac operon
Required for transport and metabolism of lactose
trp operon Codes for the production of tryptophan an
amino acid.
lac operon (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?______________________________________________
lac operon (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.
lac operon: If Lactose not Present Lacl protein: repressor protein of lactose
metabolism Binds to the lac operon operator,
preventing RNA polymerase from transcribing the lac operon genes.
Operon and operator actually overlap, so RNA poly cannot bind to DNA.
lac operon: If lactose IS present If lactose present, lacl must be removed
from operator so lac operon 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!
trp operon (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 trp operon.
Trp operon: when trp is not present
Inactive repressor is not blocking operator.
RNA polymerase can transcribe operon.
Trp operon: 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!)
http://www.youtube.com/watch?v=oBwtxdI1zvk
Seatwork/Homework Page258, #1-6.