BSC2010 Tang Exam 3 Receptor tyrosine kinase http www youtube com watch v ObrsQl vPA4 g protein coupled receptor http www youtube com watch v qOVkedxDqQo ion channel receptors http www youtube com watch v uo5lZe4IGDo mitosis http www youtube com watch v cvlpmmvB m4 http www youtube com watch v gTZ vj HdzM dna replication http www youtube com watch v teV62zrm2P0 protein synthesis http www youtube com watch v p VLBmX1ExM http www youtube com watch v T1DV tDaKEo src vid p VLBmX1ExM feature iv annotation id annotation 944248 mrna degradation http www youtube com watch v h7FHqaetMS0 viral reproductive cycle http www youtube com watch v EqK1CYYQIug Lecture 22 Chapter 11 Cell Signaling Distinguish between local and long distance cell signaling o In both local and long distance signaling only specific target cells recognize and respond to a given signaling molecule o Local signaling includes Direct cell cell contact GAP junctions animal cells Plasmodesmata plant cells Auto and paracrine signaling Paracrine signaling A secreting cell acts on nearby target cells by discharging molecules of a local regulator into the extracellular fluid Synaptic Signaling A nerve cell releases neurotransmitter molecules into a synapse stimulating the target cell o Long distance signaling includes Hormonal signaling Specialized endocrine cells secrete hormones into body fluids often the blood Hormones may reach virtually all body cells Describe the three general stages of cell signaling Cell signaling process helps ensure that crucial activities occur in the right cells at the right time in proper coordination with the activities of other cells of the organism o Reception the target cell s detection of a signaling molecule coming from outside the cell A chemical signal is detected when the signaling molecule binds to a receptor protein located at the cell s surface or inside the cell SIGNAL MUST BE RECOGNIZED o Transduction the binding of the signaling molecule changes the receptor protein in some way initiating this process This stage converts the signal to a form that can bring about a specific cellular response Sometimes occurs in a single step but more often then not requires a sequence of changes in a series of different molecules SIGNAL MUST BE CHANGED TO DIFFERENT FORM o Response the transduced signal triggers a specific cellular response The response could be any imaginable cellular activity Describe the three types of plasma member receptors o G protein coupled receptors cell surface transmembrane receptor that works with the help of a G protein a protein that binds the energy rich molecule GTP Loosely attached to the cytoplasmic side of the membrane the G protein functions are a molecular switch that is either on or off depending on which of GDP or GTP is attached When GDP is bound to the G protein the G protein in inactive When the appropriate signaling molecule binds ot the extracellular side of the receptor the receptor is activated and changes shape Its cytoplasmic side then binds an inactive G protein causing a GTP or displace the GDP This activates the G protein The activated G protein dissociates from the receptor diffuses along the membrane and then binds to an enzyme altering the enzyme s shape and activity Once activated the enzyme can trigger the next step leading to a cellular response It then hydrolyzes its bound GTP to GDP Now inactive again the G protein leaves the enzyme which returns to its original state and the G protein is now available for reuse The GTPase function of the G protein allows the pathway to shut down rapidly when the signaling molecule is no longer present o Receptor tyrosine kinases characterized by having enzyme activity A kinase is an enzyme that catalyzes the transfer of phosphate groups Many receptor tyrosine kinases have the structure depicted schematically Before the signaling molecule binds the receptors exist as individual units referred to as monomers Each has an extracellular binding site an alpha helix spanning the membrane and an intracellular tail containing multiple tyrosines The binding of a signaling molecule causes two receptor monomers to associate closely with each other forming a complex known as a dimer Dimerization activates the tyrosine kinase region of each monomer each tyrosine kinase adds a phosphate from an ATP molecule to a tyrosine on the tail of the other monomer Now that the receptor is fully activated specific relay proteins inside the cell recognize it Each such protein binds to a specific phosphorylated tyrosine undergoing a resulting structural change that activates the bound protein Each activated protein triggers a transduction pathway leading to a o Ion channel receptor contains a region that acts as a gate when the receptor cellular response changes shape gate opens or closes sides When a signaling molecule binds to a ligand to the receptor protein the These proteins bind the ligand at a specific site on their extracellular Gate remains closed until ligand binds with receptor When the ligand binds to the receptor and the gate opens specific ions can flow through the channel and rapidly change the concentration of that particular ion inside the cell When the ligand dissociates from this receptor the gate closes and ions no longer enter the cell Understand the specificity of interaction between a ligand and a receptor o Ligand the term for molecule that specifically binds to another molecule often a larger one o Ligand binding usually causes a receptor protein to undergo a change in shape o For many receptors this shape change directly activates the receptor enabling it to interact with other cellular molecules o For other kinds of receptors the immediate effect of ligand binding is to cause the aggregation of two or more receptor molecules which leads to further molecular events inside the cell o The explanation for the specificity exhibited in cellular responses to signals is the same as the basic explanation for virtually all differences between cells o Because different kinds of cells turn on different sets of genes different kinds of cells have different collections of proteins In general terms explain the role of second messenger in signal transduction o Second messengers small water soluble and can readily spread throughout the cell by diffusion o Second messengers participate in pathways that are initiated by both G protein coupled receptors and receptor tyrosine kinase o Second messengers can be rapidly produced and
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