Ligand gated ion channels 4 internal steroid hormone

This preview shows page 19 - 22 out of 58 pages.

Ligand-gated ion channels 4. Internal (steroid hormone receptors) VIII. G- protein linked receptor A. There are 7 transmembrane protein, integral proteins, needed to structurally hold the protein to the membrane B. Has a signal binding site, that is similar to a catalytic site in that recognizes a specific signal C. Signal binding is a very weak bond D. G stands for GTP: a triphosphate nucleotide, is an energy carrier IX. Enzyme receptor A. They have enzymatic activities themselves 1. Example: tyrosine kinase receptor (receptor for growth factors) 2. The extracellular part binds the ligand (signal 3. The intercellular part acts as an enzyme a) Compare to g protein linked receptors, which do not have enzymatic activity, but are linked to g proteins B. Tyrosine kinase receptor
20 1. It is a protein kinase enzyme that phosphorylates (attach phosphate group) tyrosine residues within proteins a) That phosphate group comes from ATP X. Internal receptors A. If a signal can pass through the cell membrane, then there is no need for extracellular receptors B. instead , the cell uses intracellular receptors to receive such signals C. Theses signals include hydrophobic molecules- such as steroids and thyroid hormones (lipids) of animals, and small gaseous molecules, such as ethylene and nitric oxide, in plants that can diffuse into cells XI. Signal transduction pathway A. Membrane receptors: have a multistep pathway, and must carry information from the outside of the cell to the inside B. Internal receptors can carry out the transduction themselves C. Multi-step signal transduction 1. Advantages a) Amplification of signal: one signal can transmit information to multiple molecules at each step b) regulation : more steps means more checkpoints to regulate the final response 2. Mechanics a) The signal causes conformational changes D. The major mechanism of signal transduction is phosphorylation 1. Protein kinase is an enzyme that transfers a phosphate group from ATP to a substrate protein 2. Substrates include: a) The protein kinase itself (autophosphorylation=inter or intramolecular) b) Other proteins (most cellular kinases use other proteins as substrates 3. Major protein kinases are tyrosine kinase and serine/threonine kinase 4. Phosphate group can be removed from a protein by protein phosphatase 5. Phosphorylation cascade a) Cells have thousands of different protein kinases b) Different protein kinases can phosphorylate each other regulating enzymatic activity E. Second messengers: participate in signaling pathways initiated by G protein- linked receptors and tyrosine kinase receptors. Usually ions or water soluble small molecules 1. Ca2+ a) Even more commonly used second messenger than cAMP; it functions as a second messenger in: (1) Muscle contraction (2) Cell division (3) Secretion of many substances (4) Plant adaptation in cold and heat plant response to touching b) Calcium ions functions in signaling pathways mediated by both G-
21 protein linked receptors and tyrosine kinases receptors c) Normally [Ca^2+] outside the cell> [Ca^2+] inside the cell d)

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture