For example, the virus that causes human influenza (flu) binds specifically to receptors on membranes of cells of the respiratory system. Viruses often bind to cell-surface receptors on the host cell. To reproduce, viruses must invade a living cell, which serves as a host, and then take over the host’s cellular apparatus. Some viruses are simply composed of an inert protein shell containing DNA or RNA. Unlike living cells, many viruses do not have a plasma membrane or any of the structures necessary to sustain life. Errors in the protein structures of certain receptor molecules have been shown to play a role in hypertension (high blood pressure), asthma, heart disease, and cancer. The size and extent of each of these domains vary widely, depending on the type of receptor.īecause cell-surface receptor proteins are fundamental to normal cell functioning, it should come as no surprise that a malfunction in any one of these proteins could have severe consequences. The ligand-binding domain is also called the extracellular domain. Cell-surface receptors are also called cell-specific proteins or markers because they are specific to individual cell types.Įach cell-surface receptor has three main components: an external ligand-binding domain, a hydrophobic membrane-spanning region, and an intracellular domain inside the cell. Ligands that interact with cell-surface receptors do not have to enter the cell that they affect. This type of receptor spans the plasma membrane and performs signal transduction, in which an extracellular signal is converted into an intercellular signal. Cell-Surface ReceptorsĬell-surface receptors, also known as transmembrane receptors, are cell surface, membrane-anchored (integral) proteins that bind to external ligand molecules. Internal receptors can directly influence gene expression without having to pass the signal on to other receptors or messengers. Transcription is the process of copying the information in a cell’s DNA into a special form of RNA called messenger RNA (mRNA) the cell uses information in the mRNA (which moves out into the cytoplasm and associates with ribosomes) to link specific amino acids in the correct order, producing a protein. The ligand-receptor complex moves into the nucleus, then binds to specific regulatory regions of the chromosomal DNA and promotes the initiation of transcription (Figure 1). When the ligand binds to the internal receptor, a conformational change is triggered that exposes a DNA-binding site on the protein. Gene expression is the cellular process of transforming the information in a cell’s DNA into a sequence of amino acids, which ultimately forms a protein. Once inside the cell, many of these molecules bind to proteins that act as regulators of mRNA synthesis (transcription) to mediate gene expression. Internal receptors, also known as intracellular or cytoplasmic receptors, are found in the cytoplasm of the cell and respond to hydrophobic ligand molecules that are able to travel across the plasma membrane. Many intracellular receptors are transcription factors that interact with DNA in the nucleus and regulate gene expression. Hydrophobic signaling molecules typically diffuse across the plasma membrane and interact with intracellular receptors in the cytoplasm.
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