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UI BIOL 1411 - Cell Signaling

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BIOL 1411 1st Edition Lecture 8Outline of Last Lecture I. Membrane Transporta. Active Transporti. Osmosis b. Passive TransportOutline of Current Lecture I. Transport of Large Molecules across membraneII. Cell Signaling a. Cells Respond to environmentb. Receptors sense signalsCurrent LectureI. How do large molecules cross membrane?- Endocytosis: plasma membrane surrounds the extracellular material and investigates, forming a vesicleo Phagocytosis- for huge molecules or entire cells are engulfed A food vacuole or phagosome formso Pinocytosis- small dissolved substances or fluidso 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 environmento Chemical- nutrients, waste, ion, hormoneo Physical Stimulus- light, sound, temp- To detect and respond to a signal, a call must have a specific receptorThese 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 initiatedo Paracrine Signaling- one cell to another cell through diffusiono Autocrine signaling- the secreting cell itself will have its own receptoro 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 pathwayo Signal o Receptor or the signalo 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 shapeo Shape activates receptor- Activated receptor alters function of a responder protein- Response is executedBig Picture 2: Receptors sense signals- Receptor-Ligand Bindingo Binding is reversibleo Ligand is not changed by bindingo The receptor alternates between active and inactive conformationso Many “behavior altering” drugs work by ligand-bonding site of receptor proteins in braincells- 2 General types of receptorso 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 GTPo No signal- inactive state, no interaction with receptors, has GDP boundo Signal binding to receptor: becomes active by binding, has GTP boundo They are not kinases, they don’t ass a phosphate to GDP they activate G proteins which switch GDP for GTPo One subunit encounters an effector protein to produce responseo The one subunit finds other 2 subunits again and switches back to GDPo G proteins can either activate or inhibit an effector Epinephrine binds to G protein-linked receptor and activates an enzyme to produce cyclic AMPo 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


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