ligand

Examples of ligand in the following topics:

• 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.

• 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.

• 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.

• 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.

• Cell Signaling and Cell Growth

  • The ligands that promote cell growth are called growth factors.

• 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.

• 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.

• 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

• 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.