HMG – Week 12 Qs

These vocabulary flashcards cover the fundamental mechanisms of bacterial gene regulation, focusing on the components, function, and mutations of the lac operon.

Gene expression regulation

The process by which bacteria control when and how much of a gene is expressed to conserve energy and respond rapidly to environmental changes.

Operon

A cluster of genes controlled by a single promoter and transcribed together into one mRNA molecule.

Transcriptional Regulation

The most important level of regulation in bacteria, involving control through promoters, operators, repressor proteins, and activator proteins.

Promoter ($lacP$)

The specific binding site on the DNA for RNA polymerase.

Operator ($lacO$)

The specific binding site on the DNA for the repressor protein.

$$lacI$$

The gene responsible for producing the repressor protein.

$$lacZ$$

The gene that encodes the enzyme $\beta$-galactosidase.

$$lacY$$

The gene that encodes lactose permease.

$$lacA$$

The gene that encodes transacetylase.

Negative Control

Regulation that occurs when a repressor protein inhibits transcription; removing the repressor allows transcription to proceed.

Allolactose

A molecule derived from lactose that binds to the repressor and causes a conformational change, preventing the repressor from binding to the operator.

Positive Control

Regulation that depends on glucose availability, specifically through the $CAP$-$cAMP$ system which increases transcription levels.

$CAP$ ($\text{Catabolite Activator Protein}$)

A protein that binds with $cAMP$ to help RNA polymerase bind to the promoter when glucose levels are low.

$$cAMP$$

A signaling molecule whose levels increase when glucose is low, necessary for forming the complex that stimulates strong transcription of the lac operon.

Constitutive expression

A condition where transcription occurs continuously (the genes remain ON) because the cell has lost its OFF switch due to mutation.

$lacI^-$ Mutation

A mutation in the $lacI$ gene that produces a defective repressor protein which cannot bind the operator.

$lacO^c$ Mutation

An operator constitutive mutation where the DNA sequence of the operator is altered so the repressor cannot recognize or bind to it.