Question

Mention the differences between the regulation of gene activity in lac operon and trp operon in E. coli.

Answer 1

Hint: In an operon, all the genes are expressed as a single unit, a single promoter is required for the initiation and regulation of transcription. The lactose or lac operon is an inducible operon whereas the tryptophan or trp operon is the repressible operon. Gene regulation activity can be positive or negative.

Complete answer:
-The operon model was first formulated by Jacob and Monod in 1961 explaining operon as a unit of gene expression and regulation. Prokaryotes have a simple mechanism for the regulation of genes, their operon consists of an operator gene, a promoter and a regulatory gene, a structural gene, a repressor and an inducer.
-The lac operon have three structural genes, an operator and a promoter whereas the trp operon have five structural genes, a promoter, a repressor, an overlapping operator site and a leader region along with an RNA attenuator.
-The lac operon responds to the inducer whereas the trp operon responds to the repressor protein.
-The activity of the promoter in lac operon is regulated by two different proteins, one preventing the RNA Polymerase from transcribing called the negative control and the other that enhances the RNA Polymerase binding to the promoter called the positive control.
-In absence of lactose or its analog the lac repressor directly binds to the operator resulting in inhibition of transcription of genes, hence the negative regulation.
-In presence of lactose or its analog, it binds to the allosteric site of the repressor and the lac repressor could not bind to the operator.
-If E. coli finds both Glucose and Lactose in the medium, it metabolizes the glucose and not the lactose but there is no such thing involved in trp operon.
-CAP (catalytic activator protein) exerts a positive control in lac operon when glucose is absent.
-In trp operon, the attenuator regulates the transcription inhibition as a function of tryptophan concentration. If trp concentration is high the ribosomes quickly translates the leader peptide and if it is low, the translation is slowed and transcription outpaces the translation.

Note: The easy way to remember the operons regulation is by learning their diagrams. Focus on one typically the lac operon and you will get the other one automatically. Also remember that lac operon is an inducer type operon and trp is a repressor type operon.