How do receptors work in cells

This type of receptor spans the plasma membrane and performs signal transduction , in which an extracellular signal is converted into an intercellular signal. Ligands that interact with cell-surface receptors do not have to enter the cell that they affect.

Cell-surface receptors are also called cell-specific proteins or markers because they are specific to individual cell types. Each cell-surface receptor has three main components: an external ligand-binding domain, a hydrophobic membrane-spanning region, and an intracellular domain inside the cell.

The size and extent of each of these domains vary widely, depending on the type of receptor. Text adapted from: OpenStax , Biology. OpenStax CNX. October 13, Sigalov, The School of Nature. Cao, X. Koh, L. The binding of these ligands to these receptors results in a series of cellular changes. These water soluble ligands are quite diverse and include small molecules, peptides, and proteins.

Nitric oxide NO is a gas that also acts as a ligand. It is able to diffuse directly across the plasma membrane; one of its roles is to interact with receptors in smooth muscle and induce relaxation of the tissue.

NO has a very short half-life; therefore, it only functions over short distances. Nitroglycerin, a treatment for heart disease, acts by triggering the release of NO, which causes blood vessels to dilate expand , thus restoring blood flow to the heart. Privacy Policy. Skip to main content. Cell Communication. Search for:. Signaling Molecules and Cellular Receptors.

Signaling Molecules and Cellular Receptors Cellular communication ensures regulation of biological processes within various environments from single-celled to multicellular organisms. Learning Objectives Explain the importance of cell communication. Key Takeaways Key Points The ability of cells to communicate through chemical signals originated in single cells and was essential for the evolution of multicellular organisms.

Cells can receive a message, transfer the information across the plasma membrane, and then produce changes within the cell in response to the message. Single-celled organisms, like yeast and bacteria, communicate with each other to aid in mating and coordination. Cellular communication has developed as a means to communicate with the environment, produce biological changes, and, if necessary, ensure survival.

Key Terms biofilm : a thin film of mucus created by and containing a colony of bacteria and other microorganisms. Forms of Signaling The major types of signaling mechanisms that occur in multicellular organisms are paracrine, endocrine, autocrine, and direct signaling. Learning Objectives Describe four types of signaling found in multicellular organisms.

Key Takeaways Key Points Cells communicate via various types of signaling that allow chemicals to travel to target sites in order to elicit a response. Paracrine signaling occurs between local cells where the signals elicit quick responses and last only a short amount of time due to the degradation of the paracrine ligands.

Endocrine signaling occurs between distant cells and is mediated by hormones released from specific endocrine cells that travel to target cells, producing a slower, long-lasting response. Autocrine signals are produced by signaling cells that can also bind to the ligand that is released, which means the signaling cell and the target cell can be the same or a similar cell.

Direct signaling can occur by transferring signaling molecules across gap junctions between neighboring cells. Types of Receptors Receptors, either intracellular or cell-surface, bind to specific ligands, which activate numerous cellular processes. Learning Objectives Compare internal receptors with cell-surface receptors. Key Takeaways Key Points Intracellular receptors are located in the cytoplasm of the cell and are activated by hydrophobic ligand molecules that can pass through the plasma membrane.

Cell-surface receptors bind to an external ligand molecule and convert an extracellular signal into an intracellular signal. Three general categories of cell-surface receptors include: ion -channel, G- protein, and enzyme -linked protein receptors.

Ion channel -linked receptors bind a ligand and open a channel through the membrane that allows specific ions to pass through. G-protein-linked receptors bind a ligand and activate a membrane protein called a G-protein, which then interacts with either an ion channel or an enzyme in the membrane. Key Terms integral protein : a protein molecule or assembly of proteins that is permanently attached to the biological membrane transcription : the synthesis of RNA under the direction of DNA.

Signaling Molecules Signaling molecules are necessary for the coordination of cellular responses by serving as ligands and binding to cell receptors. Learning Objectives Compare and contrast the different types of signaling molecules: hydrophobic, water-soluble, and gas ligands.

Key Takeaways Key Points Signaling molecules can range from small proteins to small ions and can be hydrophobic, water-soluble, or even a gas. Hydrophobic signaling molecules ligands can diffuse through the plasma membrane and bind to internal receptors. Water-soluble ligands are unable to pass freely through the plasma membrane due to their polarity and must bind to an extracellular domain of a cell -surface receptor.

Molecules that bind to receptor sites are known as ligands. Hormones, neurotransmitters, and drugs are examples of ligands. They are able to fit into specific receptor sites in the same way keys are able to fit into specific locks.

Whenever a ligand binds to a receptor site, it alters the shape of the receptor and launches a cascade of chemical reactions known as signaling. A message from the ligand makes its way into the cell, which can induce a variety of responses, including changes in gene expression.

Membrane receptors are divided into three major classes: ion channel—linked receptors, G-protein-coupled receptors, and enzyme -linked receptors. Ion channel—linked receptors reside on the cell membrane. They have a channel that spans the cell membrane and enables ions—atoms and molecules with a negative or positive charge—to freely move in and out of the cell.

Examples of ions include sodium and calcium. When a ligand binds to the receptor site on the channel, the channel opens, allowing ions to travel through the channel in milliseconds.

G-protein-coupled receptors are the largest class of receptors. These receptors work with what is known as a G-protein. G-protein-coupled receptors help the cell respond to different substances, such as hormones, neurotransmitters, and lipids. Many medical drugs work by binding to G-protein-coupled receptors. Enzyme-linked receptors are another kind of cell-surface receptor. For example, prokaryotic organisms have sensors that detect nutrients and help them navigate toward food sources.

In multicellular organisms, growth factors, hormones, neurotransmitters, and extracellular matrix components are some of the many types of chemical signals cells use. These substances can exert their effects locally, or they might travel over long distances. For instance, neurotransmitters are a class of short-range signaling molecules that travel across the tiny spaces between adjacent neurons or between neurons and muscle cells.

Other signaling molecules must move much farther to reach their targets. One example is follicle-stimulating hormone, which travels from the mammalian brain to the ovary, where it triggers egg release. Some cells also respond to mechanical stimuli. For example, sensory cells in the skin respond to the pressure of touch, whereas similar cells in the ear react to the movement of sound waves.

In addition, specialized cells in the human vascular system detect changes in blood pressure — information that the body uses to maintain a consistent cardiac load. Cells have proteins called receptors that bind to signaling molecules and initiate a physiological response. Different receptors are specific for different molecules.

Dopamine receptors bind dopamine, insulin receptors bind insulin, nerve growth factor receptors bind nerve growth factor, and so on. In fact, there are hundreds of receptor types found in cells, and varying cell types have different populations of receptors. Receptors can also respond directly to light or pressure, which makes cells sensitive to events in the atmosphere. Receptors are generally transmembrane proteins, which bind to signaling molecules outside the cell and subsequently transmit the signal through a sequence of molecular switches to internal signaling pathways.

Membrane receptors fall into three major classes: G-protein-coupled receptors, ion channel receptors, and enzyme-linked receptors. The names of these receptor classes refer to the mechanism by which the receptors transform external signals into internal ones — via protein action, ion channel opening, or enzyme activation, respectively. Because membrane receptors interact with both extracellular signals and molecules within the cell, they permit signaling molecules to affect cell function without actually entering the cell.

This is important because most signaling molecules are either too big or too charged to cross a cell's plasma membrane Figure 1. Not all receptors exist on the exterior of the cell. Some exist deep inside the cell, or even in the nucleus.

These receptors typically bind to molecules that can pass through the plasma membrane, such as gases like nitrous oxide and steroid hormones like estrogen. Figure 1: An example of ion channel activation An acetylcholine receptor green forms a gated ion channel in the plasma membrane. This receptor is a membrane protein with an aqueous pore, meaning it allows soluble materials to travel across the plasma membrane when open.