codes for the production of a repressor protein

A regulator gene is a prokaryotic gene that

An operator is a DNA segment that controls transcription by

An intron is a section of a gene that is transcribed but not translated.

An exon is a section of a gene that is transcribed and translated.

transcription by binding to RNA polymerase and to an enhancer.

A transcription factor is a protein that facilitates gene

blocking RNA polymerase with a repressor protein; it is part of the operon.

C

D

A

B

D

Without a nuclear envelope, there is no structure to separate newly synthesized RNA from ribosomes. Therefore, ribosomes can begin to translate the RNA as soon as it is formed, before it has had a chance to be modified.

A series of genes whose transcription is controlled by a single promoter and operator.

Lactose bonds to the repressor protein, releasing it from the operator. This allowsthe lactase genes to be transcribed and translated.

In the absence of lactose, the repressor protein binds to the operator, preventing transcription of the lactase genes.

regulator gene

lactose

repressor protein

promoter

operator

If the regulator gene were deleted then the repressor protein could no longer be produced. Without a repressor protein at the operator site, RNA polymerase would transcribe genes continuously.

Transcription is activated because the lactose molecule has bound to the repressor protein. This causes the repressor protein to release from the operator site, which then permits RNA polymerase to transcribe the structural genes.