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A regulator gene is a prokaryotic gene that
codes for the production of a repressor protein
An operator is a DNA segment that controls transcription by
blocking RNA polymerase with a repressor protein; it is part of the operon.
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.
A transcription factor is a protein that facilitates gene
transcription by binding to RNA polymerase and to an enhancer.
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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 allows
the 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.
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.
lactose
repressor protein
promoter
regulator gene
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.