BIOL 1411 1st Edition Lecture 9 Outline of Last Lecture I Transport of Large Molecules across membrane II Cell Signaling a Cells Respond to environment b Receptors sense signals Outline of Current Lecture I Cytoplasmic Receptors II Transduction and Amplification of Signal III Direct cell to cell interaction and communication Current Lecture Cytoplasmic receptors Small nonpolar molecules and steroids can pass through the cytoplasmic membrane Big Idea 3 How is an extracellular signal continued or transduced to actually affect the cell Transduction and Amplification of Signal Receptor ligand complex does not itself produce the effects in the target cell most cases Signal transduction events mediate the effects of signal receptor binding o Direct signal transduction occurs at plasma membrane and results from receptor itself initiating cellular response by effector proteins o Indirect signal transduction other molecules mediate and amplify the original signal inside the cell Receptor Protein Kinase cell response G protein linked receptors cAMP cell responses o Protein Kinase cascades often used as signal transducers and amplifiers Several kinases in which one phosphorylates and activated the next In direct transduction the first kinase is the activated receptor At each step the signal is amplified Information that arrived at the plasma membrane can be communicated to the nucleus Many steps provide specificity o G protein linked preceptor pathway These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Involves a second messenger cytoplasmic molecules produced as a result of membrane receptor ligand interaction mediates the cell s response to the signal First example cAMP Discovered in liver cells as the intermediate between the epinephrine receptors in the membrane and the cytoplasmic enzyme glycogen phosphorylase cAMP is made from ATP by adenylyl cyclase enzyme 2 major target types o Binds to ion channels in many kinds of sensory cells and opens the channel o Binds to protein kinases in cytoplasm and starts a protein kinase cascade Common means of signal transduction 2nd messengers effect many processes and allow a cell to respond in many ways to a single event at the plasma membrane 2nd messengers greatly amplify the signal 2nd messengers are not themselves proteins but acts as cofactors or regulators of a variety of target protiens Common second messengers cAMP IP3 and DAG Ca NO PIP2 in plasma membrane creates 2 second messengers DAG hydrophobic part embedded in plasma membrane IP3 hydrophilic part projects into cytoplasm Both activate PKC that has a lost of targets in the cell o How signal transductions are highly regulated Cells regulate the activity of transducer molecules to respond to signal and then return to original state to maintain responsiveness NO is unstable its concentration is regulated by how much is made Cytoplasmic concentration of CA2 depends on activity of membrane pumps and ion channels Proteins kinases G proteins and cAMP are regulated by enzymes that convert the activated form back to inactive form o What are some activities cells do once they receive a signal Effects depend on the type of cell and the signal Nervous system cells Acetycholine opening of ion channels Cells involved in nutrient metabolism and maintaining internal homeostasis liver cells Epinephrine Actively dividing or differentiating populations of cells Growth factors steroid hormones o Odorant molecules bind to receptors in the nose and a G protein is activated This activated adenylyl cyclase to catalyze formation of cAMP which opens ion channels o A cascade of reactions leads to altered enzyme activity Direct Cell to Cell interaction and communication o Cells of multicellular organisms also have direct mecanisms of interactions o Tissue formation and maintenance Cell cell recognition involves carbohydrates and proteins on plasma membrane or cell wall o Direct cell cell communication mechanisms Gap junctions in animals made from 2 connexons each made from connexin proteins too small for macromolecules ATP small sugars amino acids 2nd messengers can pass Plasmodesmata in plants membrane lined tunnels desmotubule fills the space in the plasmodematata