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Unformatted text preview: Bio 1510 Basic Life Mechanisms Fall 2008 Dr. Rasheeda Zafar Lecture # 9 Cell Communication 1 Cell Communication Communication between cells Ligand The signaling molecule Receptor protein The molecule to which the signal binds May be on the plasma membrane or within the cell 2 Cell Signaling 3 Cell Communication Four basic mechanisms Direct contact Paracrine signaling Endocrine signaling Synaptic signaling 4 Cell Communication Direct contact Molecules on the surface of one cell are recognized by receptors on the adjacent cell Paracrine signaling Signal released from a cell has an effect on neighboring cells 5 Cell Communication Endocrine signaling Hormones released from a cell affect other cells throughout the body Synaptic signaling Nerve cells release the signal (neurotransmitter) which binds to receptors on nearby cells 6 Cell Communication Signal Transduction Cell response when ligand binds to receptor protein Events within the cell that occur in response to a signal Different cell types can respond differently to the same signal 7 Cell Communication A cell's response to a signal often involve activating or inactivating proteins Phosphorylation
A common way to change the activity of protein Protein kinase An enzyme that adds a phosphate to a protein Phosphatase An enzyme that removes a phosphate from a protein
8 Receptor Types Receptors can be defined by their location Intracellular receptor Located within the cell Cell surface receptor or membrane receptor Located on plasma membrane to bind a ligand outside the cell 9 Receptor Types Three subclasses of membrane receptors Channel linked receptors Enzymatic receptors G protein-coupled receptor 10 Receptor Types Channel Linked Receptors Ion channel that opens in response to a ligand 11 Receptor Types Enzymatic Receptors Receptor is an enzyme that is activated by the ligand 12 Receptor Types G protein-coupled receptor G-protein (bound to GTP) assists in transmitting the signal 13 Intracellular Receptors Steroid hormones Have a nonpolar lipid-soluble structure Can cross the plasma membrane to a steroid receptor Usually affect regulation of gene expression An inhibitor blocks the receptor from binding to DNA until the hormone is present 14 Intracellular Receptors Steroid receptor has 3 functional domains Hormone-binding domain DNA binding domain Domain that interacts with coactivators to affect gene expression 15 Intracellular Receptors 16 Receptor Kinases Receptor tyrosine kinases Membrane receptor When bound by a ligand, the receptor is activated by dimerization and autophosphorylation Activated receptor adds a phosphate to tyrosine on a response protein An example is the insulin receptor 17 Receptor Kinases 18 Receptor Kinases Insulin receptor 19 Receptor Kinases Kinase cascade Series of protein kinases that phosphorylate each other in succession Amplifies the signal because a few signal molecules can elicit 20 Receptor Kinases Mitogen activated protein (MAP) kinases Avtivated by kinase cascade 21 G-Protein Coupled Receptors G-protein G-protein Protein bound to GTP G-protein-coupled receptor (GPCRs) Receptors bound to G proteins G-protein is a switch turned on by the receptor G-protein then activates an effector protein (usually an enzyme) 22 G-Protein Coupled Receptors 23 G-Protein Coupled Receptors The effector protein produces a second messenger. Second messenger generates the cellular response to the original signal Example one common effector protein is adenylyl cyclase which produces cAMP as a second messenger.
2+ Other second messengers include inositol phosphates, 24 G-Protein Coupled Receptors 25 Cell-to-Cell Interactions Cells can identify each other by cell surface markers. Glycolipids are commonly used as tissue-specific markers Major histocompatibility complex (MHC) proteins are used by cells to distinguish "self" from "nonself" 26 Cell-to-Cell Interactions Cell Junctions Connection between cells within a tissue Three major types Tight Junctions Anchoring Junctions Communicating junctions Gap junctions In animal cells Plasmodesmata In plant cells
27 Cell-to-Cell Interactions Tight Junctions Create sheets of cells 28 Cell-to-Cell Interactions Anchoring junctions Connect the cytoskeletons adjacent cells 29 Cell-to-Cell Interactions Communicating Junctions Permit small molecules to pass between cells 30 Cell-to-Cell Interactions 31 Cell-to-Cell Interactions Gap junction Animal Cells Plasmodesmata Plant cells 32 ...
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- Spring '08