13. The Lac Operon of E Coli Flashcards
in Ecoli, there is a lac operon, what is an operon?
a functioning unit of DNA containing a cluster of genes under control of a single promoter
what is a promoter?
a sequence of DNA that RNA pol looks for to start transcription.
RNA pol binds to the promoter with the sigma factor!
what is an operator?
a segment of DNA that the regulator binds too (these can be activators or supressors
what are the three genes the Lac operon transcribes? (just the letters)
z y and a
this is B-galactoside, lactose permease and trans-acetylase (dont need to know that)
what are the two carbon sources to allow the lac operon to transcribe and bacteria grow?
carbon and lactose
what is the lac operon used for in E coli?
the transport and metabolism of lactose in E coli
what is the preferred carbon source in E coli? When is the lac operon used?
the preferred carbon source is glucose because its a monosaccharide. when lactose is present and glucose is not present the lac operon is switched on to express genes to help utilise lactose
why is the lac operon not always turned on?
as an energy preservation method. if glucose is available, the genes to metabolosie lactose are not needed!
is the lac operon a positive or negative mode of gene regulation?
its both positive and negative!
explain what a positive mode of regulation is?
- the inducer and what concentration its present at with glucose
positive - when glucose is present, there are low levels of the CAP inducer.
The CAP inducer conc is high when theres low levels of glucose, ie lactose and CAP binds to the promoter
glucose = no CAP
no glucose = CAP available to induce (start) transcription of lac operon
explain what negative control of gene regulation is in the lac operon
gene expression is turned off when the repressor is bound to the promoter DNA.
gene expression is turned on when the repressor is not bound to DNA
repressor bound - no transcription
repressor not bound - transcritpion
what is the function of the Laci gene and where is it transcribed?
its a regulatory gene located close to the z y and a genes
look at image carefully
