7.4 Controlling Gene Expression Flashcards
housekeeping genes
genes that are always required
e.g. hemoglobin
Controlling gene expression
Not all proteins are required by all cells at all times
Cells regulate gene expression in response to
their own life cycles and environmental conditions
Ex – insulin only required when blood glucose levels are high
Some genes are always required – called
housekeeping genes ex hemoglobin
prokaryotic gene control mechanisms
Gene expression in prokaryotes is regulated in
response to the concentration of two
molecules: lactose and tryptophan
Both of these responses are examples of negative feedback control
the Lac Operon
To regulate the expression of genes required for lactose metabolism, prokaryotes use what is known as the operon model
The lac operon is a cluster of three genes that code for the proteins involved in the
metabolism of lactose
what does the lac operon consist of?
promoter
operator
coding regions for the enzymes that metabolize lactose
describe how lactose is used in the lac operon
In the presence of
lactose the lactose
molecule itself binds
to the repressor protein.
This allows RNA
polymerase to bind to
the promoter and
transcribe the genes
What happens when lactose is absent in the Lac Operon?
When lactose is absent from the cell’s environment, the
active lac repressor binds to the operator of the lac operon, blocking transcription
the trp operon
Tryptophan is an amino acid which is an important
component to many proteins.
Prokaryotes can synthesis tryptophan directly or
through their environment
The trp operon has the same components as the lac operon, but repressor protein acts in a different
manner to regulate gene expression
There is a corepressor protein is a signal molecule
that binds to a repressor protein to control gene
expression
what happens when tryptophan is absent?
the trp repressor is inactive
what happens when tryptophan is present in the cell’s environment?
the amino acid binds to and activates the trp repressor
