Energy, Transport and Scavenging in Bacteria Flashcards
(39 cards)
What is the cap site for the lac operon?
cAMP/CRP complex binds to a specific sequence in the lac control region called the “CAP” site. The CAP site is just upstream from the RNA polymerase binding site.
What does CAP do in the lac operon?
The CAP binding site is a positive regulatory site that is bound by catabolite activator protein (CAP). When CAP is bound to this site, it promotes transcription by helping RNA polymerase bind to the promoter.
What are the two binding sites of the promoter?
The promoter of the lac operon has two binding sites. One site is the location where RNA polymerase binds. The second location is the binding site for a complex between the catabolite activator protein (CAP) and cyclic AMP (cAMP)
Where is the cap site found?
Promoter of the lac operon
What kind of relationship does the concentration of glucose have with cyclic AMP?
Inverse, no glucose there will be high levels of cAMP
What is cyclic AMP?
cAMP is a “hunger signal” made by E. coli when glucose levels are low. cAMP binds to CAP, changing its shape and making it able to bind DNA and promote transcription.
What is the purpose of cyclic AMP?
CAP isn’t always active (able to bind DNA). Instead, it’s regulated by a small molecule called cyclic AMP (cAMP).
What is a CAP and give an example of one
CAP is a catabolite repressor activator protein example -
CRP in bacteria
What is the effect of the cAMP-CAP complex binding to the CAP site in the promoter region?
It acts as an inducer and triggers the binding of RNA Polymerase and helps transcription process
How does the lac repressor sense lactose indirectly
Through its isomer allolactose - an inducer of the lac operon
How do catabolite activator proteins work?
act as a glucose sensor - activates transcription of the operon, but only when glucose levels are low.
How do catabolite activator proteins sense the glucose molecule?
CAP senses glucose indirectly, through the “hunger signal” molecule cAMP.
Two protein regulators turn the operon “on” and “off” in response to lactose and glucose levels, what are they?
the lac repressor and catabolite activator protein (CAP).
How do the two protein regulators of the lactose operon act as regulators?
Lac repressor - lactose sensor. It normally blocks transcription of the operon, but stops acting as a repressor when lactose is present. The lac repressor senses lactose indirectly, through its isomer allolactose.
CAP - glucose sensor. It activates transcription of the operon, but only when glucose levels are low. CAP senses glucose indirectly, through the “hunger signal” molecule cAMP
What is a lac operon?
Group of genes with a single promoter (transcribed as a single mRNA). The genes in the operon encode proteins that allow the bacteria to use lactose as an energy source.
How can bacteria such as e.coli use lactose?
To use lactose, the bacteria must express the lac operon genes, which encode key enzymes for lactose uptake and metabolism. To be as efficient as possible, E. coli should express the lac operon only when two conditions are met:
- Lactose is available, and
- Glucose is not available
What are the genes found in the lac operon and what are their functions?
- lacZ gene encodes an enzyme called β-galactosidase, which is responsible for splitting lactose (a disaccharide) into readily usable glucose and galactose (monosaccharides).
- lacY gene encodes a membrane protein called lactose permease, which is a transmembrane “pump” that allows the cell to import lactose.
- lacA gene encodes an enzyme known as a transacetylase that attaches a particular chemical group to target molecules. It’s not clear if this enzyme actually plays any role in lactose breakdown.
What does the lac Z gene encode for?
enzyme called β-galactosidase
What does the lac Y gene encode for?
membrane protein called lactose permease
What does the lac A gene encode for?
enzyme known as a transacetylase
What is negative regulation?
The binding of a specific protein (repressor) inhibits transcription from occurring
What is positive regulation?
permit RNA polymerase binding to the promoter region, thus allowing transcription to occur.
What is the promoter?
binding site for RNA polymerase, the enzyme that performs transcription.
What is the operator?
operator is a negative regulatory site bound by the lac repressor protein. The operator overlaps with the promoter, and when the lac repressor is bound, RNA polymerase cannot bind to the promoter and start transcription.
