BIOL 1411 1st Edition Lecture 8 Outline of Last Lecture I Membrane Transport a Active Transport i Osmosis b Passive Transport Outline of Current Lecture I Transport of Large Molecules across membrane II Cell Signaling a Cells Respond to environment b Receptors sense signals Current Lecture I How do large molecules cross membrane Endocytosis plasma membrane surrounds the extracellular material and investigates forming a vesicle o Phagocytosis for huge molecules or entire cells are engulfed A food vacuole or phagosome forms o Pinocytosis small dissolved substances or fluids o Receptor mediated endocytosis highly specific involves receptor proteins integral membrane proteins which bind to specific substances Receptors are in regions of the plasma membrane called coated pits coated with other proteins such as clathrin on cytoplasmic side Example how most of cholesterols get inside cells LDL low density lipid proteins Exocytosis material in vesicles is expelled secreted from a cell by fusion with the plasma membrane II Cell Signaling Big Picture Cells must respond to their environment All cells process information from the environment o Chemical nutrients waste ion hormone o Physical Stimulus light sound temp To detect and respond to a signal a call must have a specific receptor 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 When signal detected a Signal Transduction Pathway is initiated o Paracrine Signaling one cell to another cell through diffusion o Autocrine signaling the secreting cell itself will have its own receptor o Endocrine Signal diffusion not enough these signals use circulatory system to each the target cells hormones o Plants plasmodesmota allow long distance transport Components of a signal transduction pathway o Signal o Receptor or the signal o Response to signal Initiated by receptor Transduced and amplified by other molecules Ultimately causes change in target cell Specificity receptor proteins have very specific binding sites for chemical signal molecules ligands Ligand binding causes receptor protein to change shape o Shape activates receptor Activated receptor alters function of a responder protein Response is executed Big Picture 2 Receptors sense signals Receptor Ligand Binding o Binding is reversible o Ligand is not changed by binding o The receptor alternates between active and inactive conformations o Many behavior altering drugs work by ligand bonding site of receptor proteins in brain cells 2 General types of receptors o Trans membrane receptor binds to large or polar molecule outside of cell Ion channel receptors allow ions to enter or leave cell Protein Kinase Receptor trans membrane protein that also have a cytoplasmic kinase domain that catalyzes phosphorylation of themselves and other proteins A phosphate is transferred form ATP to the proteins shape change to active state Example mammalian insulin receptor G protein linked receptor 7 trans membrane domains with a cytoplasmic domain that binds a G protein When extracellular domain binds ligand the shape of the cytoplasmic region changes and exposes a binding site for a G protein G Proteins mobile membrane proteins with 3 subunits They bind GDP and GTP o No signal inactive state no interaction with receptors has GDP bound o o Signal binding to receptor becomes active by binding has GTP bound o They are not kinases they don t ass a phosphate to GDP they activate G proteins which switch GDP for GTP o One subunit encounters an effector protein to produce response o The one subunit finds other 2 subunits again and switches back to GDP o G proteins can either activate or inhibit an effector Epinephrine binds to G protein linked receptor and activates an enzyme to produce cyclic AMP Cytoplasmic receptors nonpolar signal diffuses through plasma membrane to inside or cell testosterone estrogen Bind ligands that can cross the plasma membrane Ligand binding causes receptor to change shape allows it to enter nucleus where it affects gene expression The receptor is the responder and the effector