gene expression

Operon

A group of genes that can be turned off and on.

Promoter

The region where RNA polymerase attaches to initiate transcription.

Operator

The on/off switch for gene regulation.

Repressible

A system that is usually on but can be turned off.

Inducible

A system that is usually off but can be turned on.

Regulatory gene

Produces a repressor protein that binds to the operator to block transcription.

Lac operon

An example of an inducible operon that controls the synthesis of lactase.

Trp operon

An example of a repressible operon that controls the synthesis of tryptophan.

Chromatin

Eukaryotic DNA that is wrapped around proteins known as histones, forming nucleosomes.

Histone Acetylation

The addition of an acetyl group to histones, loosening DNA for transcription.

DNA methylation

The addition of a methyl group to DNA, which inhibits transcription.

Transcription factors

Proteins that bind to control elements to regulate gene expression.

Enhancers

Control elements that increase gene expression when activators bind to them.

Silencer

Control elements that reduce gene expression when repressors bind to them.

RNAP I

RNA polymerase I, which produces rRNA (highest in the nucleus).

RNAP II

RNA polymerase II, which produces mRNA and snRNA.

RNAP III

RNA polymerase III, which produces tRNA.

Alternative splicing

A process where a single gene can code for more than one protein.

RNA interference (RNAi)

A regulatory mechanism where microRNA inhibits translation of target mRNA.

MicroRNA (miRNA)

A type of noncoding RNA that matches target mRNA to inhibit its translation.

Small interfering RNA (siRNA)

Artificially created RNA used to silence gene expression.