Operons

Exam 3 -(Final Set 7)

Gene regulation

1. replication level- Error in copying DNA may cause defects

2. transcription level- Error in polymerization may cause defects

3. post transcriptional level- RNA splicing

4. translational level - error in mRNA and tRNA may cause defects

Transcription Prokaryotes

• Different sigma factors will be expressed in response to different conditions

Gene regulation in prokaryotes

Observed in initiation of transcription which takes place in the expression of the RNA polymerase at the promoter site.

Promoter site

Positive- Activators regulation

Negative- Repressors regulation

Operon

a group of functionally related genes located together in a genome

Operon

has promoter, operator, more structural gene that encode protein

Lac Operon

inducible operon ——-lacZ, lacY, lacA

lacZ, lacY, lacA

metabolize lactose through the activity of b-galactosidase

Z gene

codes for B galactosidase which catalyzes the hydrolysis of lactose into glucose and galactose

Y gene

codes for permease which regulates the lactose permeability in the cell

A gene

codes for transacetylase which assists the enzyme beta galactosidase

lacZ, lacY, lacA

expressed when lactose is present and glucose is absent

lac repressor

blocks the transcription of the operon( in presence of lactose it doesn’t act as repressor)

Catabolite activator protein (CAP)

activate transcription of operon only when glucose levels are low

Lactose

acts as inducer and binds to the repressor protein (negatively regulated)

lacl

codes for repressor protein (constant or constitutive)

Repressor protein binds to

lac operon regulatory region called operator (O)

Glucose

preferred of lactose as the fuel source

Trp operon

repressible operon that control production of tryptophan

always on

Operons

clusters of functionally related genes controlled by a single promoter