Gene regulation Flashcards
gene regulation
the process of turning genes on and off. this is controlled by switching transcription on and off and ensures that genes are expressed at appropriate times
why is gene regulation important
can prevent unnecessary energy being used to produce proteins that are not required by the organism
structural genes
code for proteins that are involved in the structure and/or function of the cell
what are the two types of genes
structural and regulatory
regulatory genes
code for proteins that control the expression of other genes such as repressor proteins and activator proteins
what is an operon
a group of genes under the control of a common promoter and operator region, these genes are all transcribed at the same time
where is the regulatory gene that codes for the repressor protein
located upstream from the trp operon
when does repression take place
when there is a high concentration of free floating tryptophan
what happens when there is free floating tryptophan
regulatory gene codes for the repressor protein which binds to the tryptophan, this induces a conformational change, activating the repressor where it then binds to the operator region,blocking rna polymerase
what occurs when there is no tryptophan present
the repressor protein is realesed from the operator region, allowing rna polymerase to transcribe the 5 structural genes
when does attentuation occur
when there is a high amount of trypophan bound to trna molecules
what occurs (steps) when tryptophan is not present free floating or trna
the ribosome translating the mrna pauses at the 2 tryptophan stop codons (UGG), waiting for the trna molecule to carry the tryptophan in. this allows 2 to pair with 3, creating an anti-attenuator loop and preventing 3 from pairing with 4.
why does the anti-attenuator loop not stop transcription
because it is further away from the attenuator sequence, the mrna does not pull away from the dna, and the ribosome and rna polymerase continues along, transcribing and translating trpE-trpA
what occurs (steps) when tryptophan is bound to trna
the ribosome runs past the tryptophan codons and stops at the stop codon (UGA), this prevents 2 from pairing with 3, so 3 pairs with 4, forming the attenuator stem loop
what does the attenuator stem loop do
as it is closer, it puts pressure on the attenuator sequence, so the mrna pulls away from the dna and the rna polymerase flies off, ending transcription
