BIOE 1010 Week 12 Notes
BIOE 1010 Week 12 Notes BIOE 1010
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This 6 page Class Notes was uploaded by Sara Littlejohn on Thursday March 24, 2016. The Class Notes belongs to BIOE 1010 at Clemson University taught by Dr. Vladimir Reukov in Spring 2016. Since its upload, it has received 11 views. For similar materials see Biology for BioEngineers in Bioengineering at Clemson University.
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Date Created: 03/24/16
Cell Signaling Module 6-1 3/23/2016 Cell Communication Responses: cells change their metabolism, their morphology, grow, die, migrate, adhere, or differentiate Signals: proteins, peptides, amino acids, nucleotides, steroids, fatty acid derivatives, to even dissolve gas molecules General Principles of Cell Signaling Reception: Information comes as the signal (primary messenger) and stimulates a target cell by binding to and activating a specific receptor Signal transduction: the receptor converts the primary messenger into a second messenger Response: the second messenger: o Activates cellular responses o Causes changes in gene expression Forms of Cell Signaling Autocrine: a cell targets itself o Produced by signaling cells that can also bind to the ligand that is released. o The signaling cell and the cell can be the same or similar cell Signaling across gap junctions: a cell targets a cell connected by gap junctions o Gap junctions are connections between the plasma membranes of neighboring cells. o These water-filled channels allow small signaling molecules, called intracellular mediators, to diffuse between the two cells Paracrine: a cell targets a nearby cell o Signal molecules diffuse locally o Example: neurotransmitters Endocrine: a cell targets a distant cell through the bloodstream o Endocrine signals originate in endocrine cells which are located in endocrine glands ( such as the thyroid gland, the hypothalamus, and the pituitary gland) o The ligands released in endocrine signaling are called hormones Types of Receptors: Internal Receptors o Hydrophobic signaling molecules typically diffuse across the plasma membrane and interact with intracellular receptor in the cytoplasm o Many intracellular receptors are transcription factors that interact with DNA in the nucleus and regulate gene expression o The ligand-receptor complex moves into the nucleus, then binds to a specific regulatory regions of the chromosomal DNA and promote the initiation of transcription Cell-Surface Receptors o Also known as transmembrane receptors, are cell surface, membrane-anchored proteins that bind to external ligand molecules o Spans the plasma membrane and performs signal transduction, in which extracellular signal is converted into an intracellular signal o Ligands that interact with cell-surface receptors do not have to enter the cell that they affect o Cell-surface receptors are also called cell-specific proteins or markers because they are specific to individual cell types Ion Channel-linked Receptors o Bind a ligand and open a channel through the membrane that allows specific ions to pass through o A ligand binds to the extracellular region causing a conformational change in protein structure allowing ions to pass through G-Protein-linked Receptors o Heterotrimeric G proteins have three subunits: alpha, beta and gamma o Signaling molecule binds a G-Protein-coupled receptor causing a GDP molecule associated with the alpha subunit to be exchanged for GTP o The beta and gamma subunits disassociate form the alpha subunit, and a cellular response is triggered. o Hydrolysis of GTP to GDP terminates the signal Enzyme-linked Receptors o Cell-surface receptor with intracellular domains that ae associated with an enzyme or the intracellular domain of the receptor itself is an enzyme o When a ligand binds to the extracellular domain, a signal is transferred through the membrane, activating the enzyme o Activation of the enzyme sets off a chain of event within the cell that eventually leads to a response Signaling Molecules Small Hydrophobic Molecules o Can diffuse directly across the membrane into the cell Water-Soluble Ligands o Polar o Bind to extracellular domain of cell-surface receptors Gases o Cause blood vessels to dilate Methods of Intracellular Signaling Phosphorylation o One of the most common chemical modifications that occurs in signaling pathways is the addition of a phosphate group to a molecule such a s a protein in a process called phosphorylation Second Messengers o Small molecules that propagate a signal after it has been initiated by the binding of the signaling molecule to the receptor Response to the Signal Gene Expression o Some signal transduction pathways regulate the transcription of RNA o Others regulate the translation of proteins form mRNA Increases in Cellular Metabolism o Adrenaline (epinephrine) is a hormone that readies the body for short term emergencies Cell Growth o Cells do not normally divide unless they are stimulated by signal from other cells o The ligands that promote cell growth are called growth factors Cell Death o Programmed cell death is called apoptosis o Apoptosis allows a cell to die in a controlled manner that prevents the release of potentially damaging molecules from inside the cell