What is a ligand in cell biology?
In biochemistry and pharmacology, a ligand is a substance that forms a complex with a biomolecule to serve a biological purpose. In protein-ligand binding, the ligand is usually a molecule which produces a signal by binding to a site on a target protein.
A receptor detects a signal molecule and carries out an action in response. A ligand is a molecule that acts as a signal when it binds to a receptor. A ligand that can cross the cell membrane can bind to an intracellular receptor. The cell membrane allows some, but not all, molecules to cross.
- Hormone receptor. A hormone receptor is a receptor molecule that binds to a specific hormone. Hormone receptors are a wide family of proteins made up of receptors for thyroid and steroid hormones, retinoids and Vitamin D, and a variety of other receptors for various ligands, such as fatty acids and prostaglandins.
- While active transport requires energy and work, passive transport does not. There are several different types of this easy movement of molecules. It could be as simple as molecules moving freely such as osmosis or diffusion.
- Ligand. Molecule that specifically bonds to a larger molecule. Ligand binding causes a receptor protein to undergo a change in shape, which sometimes directly activates the receptor which allows it to interact with other cells. The signaling molecule behaves as a ligand.
The most important property of the cell membrane is its selective permeability: some substances can pass through it freely, but others cannot. Small and nonpolar (hydrophobic) molecules can freely pass through the membrane, but charged ions and large molecules such as proteins and sugars are barred passage.
- Permeability of phospholipid bilayers. However, the bilayer is impermeable to larger polar molecules (such as glucose and amino acids) and to ions. Although ions and most polar molecules cannot diffuse across a lipid bilayer, many such molecules (such as glucose) are able to cross cell membranes.
- Scattered in the lipid bilayer are cholesterol molecules, which help to keep the membrane fluid consistent. Membrane proteins are important for transporting substances across the cell membrane. They can also function as enzymes or receptors.
- Cholesterol acts as a bidirectional regulator of membrane fluidity because at high temperatures, it stabilizes the membrane and raises its melting point, whereas at low temperatures it intercalates between the phospholipids and prevents them from clustering together and stiffening.
Receptor Proteins Exhibit Ligand-Binding and Effector Specificity. As noted earlier, the cellular response to a particular extracellular signaling molecule depends on its binding to a specific receptor protein located on the surface of a target cell or in its nucleus or cytosol.
- In biochemistry and pharmacology, a ligand is a substance that forms a complex with a biomolecule to serve a biological purpose. In protein-ligand binding, the ligand is usually a molecule which produces a signal by binding to a site on a target protein.
- The prototypic ligand-gated ion channel is the nicotinic acetylcholine receptor. It consists of a pentamer of protein subunits (typically ααβγδ), with two binding sites for acetylcholine (one at the interface of each alpha subunit).
- Extracellular signalling molecules are cues, such as growth factors, hormones, cytokines, extracellular matrix components and neurotransmitters, designed to transmit specific information to target cells.
Updated: 2nd October 2019