Prokaryotic Gene regulation

Week 7:Prokaryotic gene expression

Define and relate the terms operon, polycistronic mRNA, and structural gene.

The operon is the region of DNA consisting of the promoter, operator, and coding sequence of the genes.

Polycistronic mRNA is prokaryotic mRNA because it contains multiple structural genes within it. For

these structural genes to be expressed, the operon must not be bound to by the repressor protein so that RNA 

Polymerase can initiate transcription

•Label a diagram of the lac operon and state the function of each component.

lacI-encodes repressor protein

lacO-operator; where repressor protein binds

lacP-promoter that recruits RNA Polymerase complex and initiates transcription

lacZ-gene for B galactosidase which cleaves lactose

lacY-gene for lactose permease which transports lactose from an external medium into the cell

RNA polymerase=initiates transcription

Repressor protein=when binds to lacO, halts transcription 

Lactose=inducer because it binds to repressor

CRP-cAMP binding site=site where cAMP can bind which speeds up transcription. cAMP levels are high when

nutritional needs of cells (glucose) are low

•Identify proteins and small molecules that regulate the expression of the lac operon.

The lac operon is negatively regulated by lacI which encodes the repressor protein. This is because when the

repressor protein is present, then transcription cannot occur. 

The lac operon is positively regulated by CRP-cAMP because it activates gene expression upon binding

•Describe how the lac repressor and CRP regulate the expression of the lac operon.

Lac repressor turns off transcription (think of a light switch) while CRP speeds up/slows down transcription

Depending on cells nutritional needs (think of volume dial)

By the time you take the final exam you should also be able to:

•Identify the differences between positive and negative forms of regulation.

Positive regulation turns on transcription while negative regulation turns off transcription

•Interpret data as it relates to the lac operon and other similar methods of regulation.

•Predict whether gene expression of an operon will occur given specific environmental conditions.

High glucose/no lactose = now transcription

High glucose/low lactose = low transcription

Low glucose/high lactose = high transcription

Low glucose/low lactose = low transcription

•Identify changes in gene expression based on the haplotypes found in the cell (i.e. using

partial diploids).