Chapter 11.2 notes

β-galactosidase

An enzyme that breaks down lactose into glucose and galactose, encoded by the Z gene in the lac operon.

Permease

An enzyme required to transport lactose into the cell, encoded by the Y gene in the lac operon.

Transacetylase

An enzyme with a dispensable and as yet unknown function, induced along with β-galactosidase and permease, encoded by a separate A gene.

Cis-acting

A term used to describe mutations or elements that influence the expression of genes only on the same DNA molecule.

Trans-acting

Refers to mutations or proteins that can regulate gene expression on any copy of the target DNA, regardless of its location.

Constitutive mutations

Mutations that cause the structural genes to be expressed continuously, regardless of the presence of an inducer.

Operator

A segment of DNA that acts as a binding site for the repressor protein; mutations can lead to constitutive expression of the gene.

Repressor protein

A protein that inhibits the transcription of a gene by binding to the operator.

Inducer

A molecule that initiates gene expression, such as allolactose or synthetic inducers like IPTG.

Catabolite repression

A regulatory mechanism that prevents the synthesis of enzymes for lactose metabolism when glucose is present.

Allostery

A regulatory mechanism in which the binding of an inducer alters the shape of a repressor, affecting its ability to bind DNA.

Superrepressor (S I) mutations

Mutations that cause the repressor to remain bound to the operator even in the presence of an inducer, preventing transcription.

Promoter

A DNA sequence that serves as the initiation site for transcription by RNA polymerase.

IPTG (Isopropyl-β-D-thiogalactoside)

A synthetic inducer used in experiments that is not hydrolyzed by β-galactosidase but still induces enzyme expression.

F' factor

A plasmid that carries one or more bacterial genes, which can be transferred between bacteria.