Gene expression

is regulated by proteins that bind to specific base sequences in DNA.

The diagram shows different places where proteins can bind. Often they bind to allow or stop RNA polymerase from attaching to the promotor region. This means the gene can be switched on or off.

“Transcription Factors” https://commons.wikimedia.org/wiki/File:Transcription_Factors.svg#/media/File:Transcription_Factors.svg

This means that environment of a cell and of an organism has an impact on gene expression.

Cells can produce proteins that affect the expression of genes in other cells and so help control cell differentiation and other processes.