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(a) Process when Lactose absent
(b) Process when Lactose present |
Regulator gene ( R ) : contain genetic information for the synthesis of protein called
repressor .
Promoter ( P ) : Site for the
attachment of RNA polymerase
Operator ( O ) : site for the attachment of the repressor protein .
Structural Genes (S) : One to several genes determining the amino acids sequence of the protein
- (1) : lacZ - Produces B- galactosidase that functional to converts lactose to glucose & galactose
- (2) : lacY - Produces Lactose permease that functional as transport lactose into the cell
- (3) : lacA - Produce transacetylase that used to transfer an aceytl group CO-A to B -galactosidase
Operon : A group of structural genes and regulating genes that function as a unit .
( OPERON = Structural gene + Operator + Promoter )
(a) Process when Lactose absent
- The repressor attaches itself to the operator and blocked part of promoter .
- RNA Polymerase cannot bind to the promoter
- The operon is not active because transcription is blocked by repressor-operator complex.
- No transcription occur and the 3 structural enzymes cannot be synthesized.
(b) Process when Lactose Present
- Lactose enter to E.coli and converted to Allolactose ( isomer of lactose )
- Allolactose binds to the repressor protein which is produced by regulator gene.
- The repressor protein changes shapes and it cannot bind to the operator that causes the operon is activated.
- RNA polymerase binds to promoter .
- Transcription of structural genes takes place to form mRNA
- The translation of mRNA occur
- The enzymes B-galactosidase , permease and transacetylase are produced
- Lactose is hydrolysed into galactose and glucose .
