In: Biology
outline the operon theory, including the function cis-acting and trans -acting elements, using the lac operon as an example
The structure of lac operon
In the presence of lactose:
In the presence of lactose the repressor binds to lactose and fails to bind to operator, so, the RNA polymease move over the structural genes and the enzymes will be synthesized.
In the absence of lactose:
In the absece of lactose the repressor binds to operator and blocks the way to RNA polymerase, so, the enzyme synthesis will be inhibited.
Find the below table for elemented and its actions of lac operon...
Gene/element |
Function |
Mode of control |
ß-gal (lacZ) |
||
lacZ+ |
Normal gene |
- |
lacZ- |
Affects the structure of enzyme - nonfunctional |
- |
Permease (lacY) |
||
lacY+ |
Normal gene |
- |
lacY- |
Affects the structure of enzyme - nonfunctional |
- |
Trancetylase (lacA) |
||
lacA+ |
Normal gene |
- |
lacA- |
Affects the structure of enzyme - nonfunctional |
- |
Operator (lacO) |
||
lacO+ |
Normal operator |
Cis |
lacOc |
Constitutive operator, repressor cannot even super repressor also cannot bind to Constitutive operator |
Cis |
Promoter (lacP) |
||
lacP+ |
Normal promoter |
Cis |
lacP- |
RNA polymerase cannot bind |
Cis |
Repressor (lacI) |
||
lacI+ |
Normal repressor |
Trans |
lacI- |
Repressor is not produced |
Trans |
lacIs |
Superrepressor, it cannot be inactivated by inducer |
Trans |