bsc2010 ch 18 & 19 prokaryotic gene regulation

gene regulation

this is important since we have around 22,000 genes or 3 billion base pairs

• alter gene expression in response to changing environment (adaptation)

• conserving resources

transcriptional regulation

this is the primary point of control especially among bacteria

transcriptional control

type of gene expression in bacteria

control of mRNA transcription, saves energy by being slow but efficient, most common point of control

translational control

type of gene expression in bacteria

cells can quickly change which proteins are produced, mRNA is already present

post-translational control

type of gene expression in bacteria

rapid response; energetically expensive

negative control

when a regulatory protein such as a repressor binds to DNA and shuts down transcription

• trp and lac operons

positive control

when a regulatory protein such as an activator protein binds to DNA and triggers transcription

operator

in the DNA, this is a segment of it that acts like a switch to turn a gene on or off

promoter

in the DNA, this is a segment of it that RNA polymerase binds to and initiates transcription, before the operator

operon

entire stretch of DNA including the operator, the promoter, and the genes that they control

repressor

protein able to switch an operon off and prevents gene transcription by binding to the operator DNA and blocking RNA polymerase

• form of negative control

inducible operon

usually off, an inductor deactivates the repressor and turns on transcription

• lac operon

• catabolic

• active form of repressor protein

• negative gene control (prevents expression)

repressible operon

usually on, binding of a repressor to the operator to stop transcription

• trp operon

• anabolic

• inactive form of repressor protein

• negative gene control (prevents expression)

lac operon

inducible operon who’s main objective is to break down lactose

• lac operon turned on by inducer inactivating

when lactose is absent: the active repressor binds to the operator and blocks the RNA polymerase’s path

when lactose is present: the lactose (inducer) binds to the repressor and becomes an inactive repressor, changing the protein’s shape and making it denatured; the operator isn’t blocked so RNA polymerase can continue to make the enzyme able to break lactose down

corepressor

molecule that cooperates with the repressor protein to switch the operon off

trp operon

repressible operon who’s main job is to make/synthesize tryptophan

• when tryptophan is absent: by nature, the inactive repressor is already denatured so the RNA polymerase can proceed

• when tryptophan is present: the tryptophan acts as a corepressor, binding to the repressor and making it an active repressor, blocking the RNA polymerase

• this tells them that there’s enough tryptophan made and making more would waste resources

activator

stimulatory protein that aids positive gene control

• binds to the DNA sequence, interacts with RNA polymerase to make transcription happen quicker

AraC

an activator protein that transcribes the ara operon when arabinose is present

• also acts as a repressor to prevent transcription when arabinose is not present

arabinose

positive regulator for the ara operon, where the AraC protein binds to _____________

• with ________ and AraC together, transcription is sped up