ligand
(noun)
an ion, molecule, or functional group that binds to another chemical entity to form a larger complex
Examples of ligand in the following topics:
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Signaling Molecules
- Important members of this class of ligands are the steroid hormones.
- Instead, most water-soluble ligands bind to the extracellular domain of cell-surface receptors.
- 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.
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Binding Initiates a Signaling Pathway
- The ligand-binding domain is also called the extracellular domain.
- G-protein-linked receptors bind a ligand and activate a membrane protein called a G-protein.
- The same ligands are often used to initiate different signals in different cell types.
- At the initiation of the signal, a single ligand binds to a single receptor.
- Recognize the relationship between a ligand’s structure and its mechanism of action.
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Types of Receptors
- Receptors, either intracellular or cell-surface, bind to specific ligands, which activate numerous cellular processes.
- Receptors are protein molecules in the target cell or on its surface that bind ligands.
- When the ligand binds to the internal receptor, a conformational change exposes a DNA-binding site on the protein.
- Ligands that interact with cell-surface receptors do not have to enter the cell that they affect.
- G-protein-linked receptors bind a ligand and activate a membrane protein called a G-protein.
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Forms of Signaling
- In order to keep the response localized, paracrine ligand molecules are normally quickly degraded by enzymes or removed by neighboring cells.
- This is different from paracrine signaling in which local concentrations of ligands can be very high.
- Autocrine signals are produced by signaling cells that can also bind to the ligand that is released.
- In some cases, neighboring cells of the same type are also influenced by the released ligand.
- Paracrine signaling acts on nearby cells, endocrine signaling uses the circulatory system to transport ligands, and autocrine signaling acts on the signaling cell.
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Cell Signaling and Cell Growth
- The ligands that promote cell growth are called growth factors.
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Termination of the Signal Cascade
- Ligand binding to the receptor allows for signal transduction through the cell.
- One method of terminating or stopping a specific signal is to degrade or remove the ligand so that it can no longer access its receptor.
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Synaptic Transmission
- The binding of a specific neurotransmitter causes particular ion channels, in this case ligand-gated channels, on the postsynaptic membrane to open.
- The neurotransmitter diffuses across the synaptic cleft and binds to ligand-gated ion channels in the postsynaptic membrane, resulting in a localized depolarization or hyperpolarization of the postsynaptic neuron.
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Methods of Intracellular Signaling
- When signaling occurs, ligand-gated calcium ion channels allow the higher levels of Ca2+ that are present outside the cell (or in intracellular storage compartments) to flow into the cytoplasm, which raises the concentration of cytoplasmic Ca2+.
- Explain how the binding of a ligand initiates signal transduction throughout a cell
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Catabolite Activator Protein (CAP): An Activator Regulator
- CAP is a transcriptional activator that exists as a homodimer in solution, with each subunit comprising a ligand-binding domain at the N-terminus, which is also responsible for the dimerization of the protein and a DNA-binding domain at the C-terminus.