Exam 2 - Lecture 5 (operons) Key Terms Flashcards
Housekeeping Gene
Genes normally expressed in actively growing cells
-10 Element
Present in prokaryotic promoters
- a site -10 bases upstream of transcription start site that RNA polymerase can recognize
-35 element
Present in prokaryotic promoters
- a site -35 bases upstream of transcription start site that RNA polymerase can recognize
transcription factor
regulates transcription initiation in eukaryotes
- controls gene expression
operon
Set of structural genes controlled by a single promoter
- can contain numerous genes
- include promoter, operator, and many genes
polycistronic mRNA
When genes in an operon transcribe into a single mRNA, they translate independently into separate proteins (3 genes in one mRNA = 3 proteins)
operator
Sequence of DNA within an operon to which a molecule can bind to either induce or repress transcription
lac operon
Controls lactose metabolism
- inducible (usually off)
- induced by presence of allolactose
- activated by the presence of cAMP
- regulated by a repressor protein
–> negative regulation
trp operon
- controls tryptophan production
- encodes proteins involved in synthesizing a vital amino acid
- under negative regulation
- repressed by presence of tryptophan
repressor protein
A lac repressor protein binds to the operator and physically gets in RNA polymerases’ way to reduce transcription
- Example of a protein interacting with DNA on a sequence-specific level
inducible protein
Usually, it is negatively regulated because it is usually off.
In the presence of lactose, an inducible operon can be turned on by adding lactose
- Inducible operon relies on a signal to stimulate transcription
- subject to positive and negative regulation
co-inducer protein
Allolactose
The presence of allolactose inhibits the repressor protein by changing its shape
- Induced transcription
negative regulation
Something is actively stopping transcription from occurring
- The repressor protein regulates the lac operon
positive regulation
activator protein
CRP is the activator protein
- helps increase transcription (positive regulation)
- binds near the promoter to help RNA polymerase bind and begin transcription
co-activator molecule
cAMP is a co-activator molecule because it makes the CRP function
- Low glucose means high cAMP
repressible operon
The default setting is on, transcribes by default
ex) trp operon
- relies on a signal to prevent transcription
- subject to positive and negative regulation
