Mcim L11 lac operon

• Glucose and Galactose
• Galactose is inverted relative to glucose

-D-Glucose

-D-Galactose

A section of DNA that contains the genetic code for a single polypeptide

• 3
• LacZ, LacY, LacA

• -They have uninterrupted coding sequence
• -In eukaryotes exons are often interrupted by introns

• -a cluster of cistrons which are transcribed on the same mRNA
• -usually functionally related
• -coordinately regulated

• A DNA sequence that binds a repressor protein
• -located after promoter and before start codon

binds operator and blocks transcription

• -binds to repressor
• -removes repressor from operator
• -Allo-lactose

USES TH EH+ ION GRADIENT TOT RANSPORT LACTOSEINTO THE CELL.

• -- GALACTOSIDASE
• -HYDROLYSES LACTOSE TO FORM GLACTOSE AND GLUCOSE.
• -makes small amount of allo-lactose

• -TRANSACETYLASE ENZYME
• -HAS UNKNOWN FUNCTION INTHE CELL

• -CRP (cAMP receptor protein) or CAP (catabolite activator protein)
• -CRP/cAMP binds to CRP site near promotor and activates transcription of Lac

GLUCOSE

Lactose and Galactose

• cAMP decreases
• Lac operon inactivated

Lac Operon active

IPTG:  ind100% Hydro:0%

ONPG: ind 0% Hydro 100%

-a substrate for detection of beta-galactosidase activity. (enzyme assay)

-if β-galactosidase is present, it hydrolyzes the ONPG molecule into galactose and the yellow identifier o-nitrophenol.

• - B-D-GALACTOSIDASE SUBSTRATE
• - PRODUCES A BLUE PRECIPITATE
• -STAINS COLONIES.
• -NOT DIFFUSIBLE (DIFFUSIBLE ONPG COLOUR WOULD SMEAR BETWEEN COLONIES.)