Intracellular receptors are typically represented by transcription factors (i.e., glucocorticoid receptors) or proteins that interact with transcription factors. Most intracellular receptors bind to ligands that diffuse across the plasma membrane. In the cytoplasm, they become active, are transported together with the ligand to the nucleus of the cell, bind to specific DNA region, and either induce or inhibit the expression of a certain gene or group of genes. Examples of such receptors are nitric oxide receptor and steroid hormone receptor.
Most membrane receptors are represented by integral membrane proteins that bind signaling substances on the outside of the membrane and, by changing the spatial structure, generate a new signal on the inside of the cell membrane. This signal determines the transcription of specific genes and the activity of enzymes that control metabolism and interact with the cytoskeleton. These receptors are represented by various structures that specifically bind particular ligand and interact with the components of the cytoplasmic signaling pathways. Some receptors possess the enzymatic activity and modify the downstream proteins, whereas other receptors are represented by ion channels and lead to the influx of certain ions (i.e., calcium) that acivate specific enzymes.
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