BIOL 1411 1st Edition Lecture 9 Outline of Last Lecture 1 Active transport 2 Macromolecules leaving the cell 3 Cell responding to their environment 4 Receptors sense signals Outline of Current Lecture 1 Extracellular signal transduction 2 Cell s response from signal 3 Direct cell cell interaction and communication Current Lecture Chunk 3 How is an extracellular signal continued or transduced to actually affect the cell Chunks 1 2 are from last lecture Transduction and Amplification of the Signal In most cases Receptor Ligand complex does not itself produce the effects in the target cells Signal transduction events mediate the effects of signal receptor binding o Direct signal transduction Occurs at plasma membrane and results from the receptor itself initiating cellular response by effector proteins o Indirect signal transduction Other molecules mediate and amplify the original signal inside the cell 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 Receptor protein kinases cell response G protein linked receptors cAMP cell responses Protein kinase cascades o Are often used as signal transducers and amplifiers both direct and indirect o Several kinases in which each one phosphorylates and activates the next In direct transduction the first kinase is the activated receptor o At each step signal is amplified because each kinase can phosphorylate many target molecules o Information that arrived at the plasma membrane can be communicated to the nucleus o Many steps provide specificity different target proteins provide variation in respose Second messenger o A cytoplasmic molecules produced as a result of membrane receptor ligand interaction mediates the cell s response to the signal the first messenger o Cyclic AMP Discovered in liver cells as the intermediate between the epinephrine receptors in the membrane and the cytoplasmic enzyme glycogen phosphorylase Made from ATP by adenylyl cyclase enzyme Two major target types Binds to ion channels in many kinds of sensory cells and opens the channel Binds to protein kinases in cytoplasm and start a protein kinase cascade o Discovery of a second messenger Soluble chemical produced by the hormone activated membranes activated glycogen phosphorylase o Indirect Signal Transduction through Second Messengers Common means of signal transduction 2nd messenger 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 act as cofactors or regulators of a variety of target proteins channels or enymes Common 2nd messengers cAMP Inositol triphosphate IP3 and diacylglycerol DAG o Derived from phospholipid PIP2 phosphatidyl inositol biphosphate in the plasma membrane DAG Hydrophobic part embedded in plasma membrane IP3 Hydrophilic part projects into cytoplasm o Are second messengers for signals that bind to G protein linked receptor o How it works Signal binds G protein linked receptor G protein swaps GDP and GTP and becomes active Activated G protein subunit encounters and activates phospholipase C which cleaves off IP3 from PIP2 DAG stats in the membrane IP3 diffuses thru cytoplasm and contacts Ca channels in ER causing Ca ions to enter cytoplasm Ca ions and DAG together activate membrane bound protein kinase C PKC Both IP3 and DAG are needed to activate PKC PKC mediates cellular responses to the signal first messenger Calcium ions Ca Nitric oxide NO Signal transduction o Cells regulate 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 Protein kinases G proteins and cAMP are regulated by enzymes that convert the activated form back to inactive form o The balance between enzymes that activate transducers and enzymes that inactivate them determines the cellular response to a signal Chunk 4 What are some activities a cell does in response to a signal Effects depend on the type of cell and the signal Nervous system cells o Acetycholine opening of ion channels Cells involved in nutrient metabolism and maintain internal homeostasis like liver cells o Epinephrine change in enzyme activities to increase blood glucose levels Actively dividing or differentiating populations of cells o Growth factors steroid hormones differential gene transcription to make new proteins Chunk 5 Direct Cell Cell interaction and Communication Cells of multicellular organisms also have direct mechanisms of interaction Tissue formation and maintenance o Cell cell recognition Involves carbohydrates and proteins on plasma membrane of cell wall Direct cell cell communication mechanisms o Gap junctions in animals o Plasmodesmata in plants Communicating Junctions part 1 o Gap junctions are formed from two Connexons each made from connexin proteins o The passageway is too small for macromolecules o ATP small sugars amino acids and 2nd messengers can pass Plant Cells o Have several thousand plasmodesmata membrane lined tunnels that traverse the cell walls o Lining made of fused plasma membranes from both cells creates a continuous cytoplasm o A desmotubule derived from the ER fills the space in the plasmodesmata channel o Allows rapid transmission of small molecules including plant hormones