Gene Regulation and Expression: lac Operon Vocabulary

Vocabulary flashcards covering key terms, component functions, enzymes, and operational mechanisms of the lac operon.

Operon

A group or cluster of genes under the control of a single promoter that functions as a single transcription unit and is transcribed into a single mRNA strand.

lac operon structure

The structural organization of the lactose operon, consisting of a promoter, an operator, and three structural genes ($lacZ$, $lacY$, and $lacA$).

Jacob & Monod (1961)

The scientists who introduced the $lac$ operon model after studying the regulation of lactose metabolism in $E.\text{ coli}$.

Promoter

The region of DNA that serves as the attachment site for RNA polymerase to initiate transcription of structural genes.

Operator

The segment of DNA that serves as the binding site for the repressor protein to regulate gene transcription.

Structural genes

The group of genes ($lacZ$, $lacY$, and $lacA$) controlled by a single promoter that code for enzymes involved in lactose metabolism.

$$lacZ$$

The structural gene in the $lac$ operon that encodes the enzyme $\beta\text{-galactosidase}$.

$$\beta\text{-galactosidase}$$

An enzyme encoded by the $lacZ$ gene that hydrolyzes lactose into glucose and galactose.

$$lacY$$

The structural gene in the $lac$ operon that encodes the protein permease.

Permease

A transport protein encoded by the $lacY$ gene that pumps lactose into the cell by increasing cell membrane permeability to lactose.

$$lacA$$

The structural gene in the $lac$ operon that encodes the enzyme transacetylase.

Transacetylase

An enzyme encoded by the $lacA$ gene that transfers an acetyl group from acetyl-CoA to $\beta\text{-galactoside}$.

$lacI$ gene

The regulatory gene located outside the $lac$ operon that codes for the repressor protein.

Repressor protein

A protein coded by the $lacI$ gene that binds to the operator to block RNA polymerase from binding to the promoter.

Allolactose

An isomer of lactose that functions as an inducer by binding to the repressor protein, changing its shape so it cannot bind to the operator.

$lac$ operon state in the absence of lactose

The mechanism where the active repressor protein remains bound to the operator, preventing RNA polymerase from transcribing structural genes and keeping the operon OFF.

$lac$ operon state in the presence of lactose

The mechanism where allolactose inactivates the repressor protein, allowing RNA polymerase to transcribe the structural genes ($lacZ$, $lacY$, and $lacA$) and turning the operon ON.

$lacI$ gene mutation outcome

A genetic change resulting in no repressor protein being produced, leading to continuous transcription of structural genes and ongoing synthesis of $\beta\text{-galactosidase}$, permease, and transacetylase.