In a organism, the brain directs the body how to respond to stimuli from the environment. in a cell, this function is performed

In eukaryotic cells, the nucleus is an enclosed structure by a membrane that holds the genetic information, which is activated when cells receive external signals (such as environmental changes). This genetic information consists of genes that respond to cellular signaling. For instance, transcription factors that reside in the cytoplasm become activated upon receiving signals from cell membrane receptors that bond with particular signaling molecules. Following this, those transcription factors move into the nucleus to engage with specific DNA promoter regions to initiate the transcription of target genes that can react to environmental stimuli.