Theme 3 - Mod 2 - Prokaryotic Transcriptional Regulations

What are the two environmental cues that E.coli bacteria detect

Changes in glucose levels and presence of lactose

Lactose permease

Transport protein that sits in cell membrane and allows for the transport of lactose into the cell

Who discovered the operon model

Jacob and Monod

What is an operator (lacO)

On-off switch

Sequence of nucleotides near start of operon that can be regulated to allow or inhibit transcription

Binding site for repressor protein

LacI

the structural gene for the repressor protein

Promoter

Binds RNA polymerase complex

What does lacZ code for

beta-galactosidase

What does lacY code for

Lactose permease

What does negative regulation of the lac operon mean

Transcription of the genes that are required for lactose metabolism turned off

What happens in the absence of lactose

Repressor protein binds to the operator and prevents transcription from taking place

This is the state that the lac operon in most cases when glucose is present

What does the repressor protein do to the DNA

Causes DNA to twist into a loop when all 4 subunits bind to the lac operon so RNA polymerase cant bind to promoter

What does it mean when Lactose allosterically inhibits the repressor

Lactose will act as an inducer molecule by binding to the repressor protein causing the repressor protein to no longer bind to the DNA

What happens in the presence of lactose

Lactose binds to the repressor protein to stop it from binding it to DNA

What is positive regulation of the Lac operon

Promotes the production of B-galactosidase and lactose permease

How is glucose and cAMP related

The amount of cAMP and the rest of transcription of the lac operon are inversely related to the concentration of glucose

How does glucose affect adenylyl cyclase

It inhibits adenylyl cyclase so high glucose causes inactive adenylyl cyclase and low glucose causes active adenylyl cyclase

CRP-cAMP binding site

Amount of cAMP will determine whether a transcriptional activator will bind to the site and therefore the degree of positive regulation of the lac operon

Why are negative and positive transcriptional regulation important

They ensure that the cell only produces the enzymes needed for lactose metabolism on an as-per-needed basis