MindMap of the Lac Operon (MCB2023S)

- plac = Promoter for structural genes
- pi = Promoter for regulatory gene
- lacI = Regulatory gene codes for repressor protein
- lacZ = structural gene for B-galactosidase
- Maj reaction: Converts lactose to glucose + galactose
- Min reaction: Converts lactose to allo-lactose
- lacY = structural gene for B-galactosidase permease
- Transports lactose into cell
- lacA = structural gene for B-galactosidase transacetylase
- Function not known, and not super required.
- Polycistronic operon
- 1 promoter & 1 regulator transcribing 1 mRNA containing
several genes; translated into many proteins ? allows
Lactose but no glucose coordinated induction/repression.
S
1. No glucose = No inactivation of adenylate
cyclase
a. ATP produced; cAMP produced
Positive
b. CAP binds to cAMP -> activated
c. Binds to CAP site and enhances
Regulation
transcription. Regulation of T
2. Lactose present = Allolactose produced
the lac Operon Oper
a. Inducer (allolactose) inactivates
Repressor so RNA Pol can bind

Negative
Glucose but no lactose:
1. Inducer (Allolactose) absent because no
Regulation
lactose = repressor remains bound,
blocking RNA Pol
2. Glucose = adenylate cyclase inactive =
no cAMP is formed = CAP doesn?t bind to
CAP site

Neither Glucose nor Lactose:
1. cAMP is formed = CAP binds to CAP site
2. Allolactose still not formed so repressor
remains active and blocks RNA Pol




- LacI repressor protein:
- Physically linked to Lac operon but