8 (ii). Cell-cell Communication- Key ConceptsHow Do Distant Cells Communicate? Cell Signaling and CommunicationSlide 3Hormones Are Long-Distance MessengersHormones Vary Widely in Effect and StructureSlide 6Slide 7Step 1: Signal ReceptionSignal ReceptorsSlide 10Step 2: Signal ProcessingSignal Processing in Lipid-Insoluble HormonesSlide 13How Do Signal Receptors Initiate a Cellular Response?Slide 15Signal TransductionG ProteinsG Proteins and Signal TransductionSlide 19Slide 20Second MessengersSlide 22Enzyme-Linked ReceptorsResults of Signal ProcessingStep 3: Signal ResponseSlide 26Slide 27Step 4: Signal DeactivationInteractions between Signaling Pathways- cross talkQuorum Sensing in BacteriaResponses to Signaling in BacteriaSlide 32© 2011 Pearson Education, Inc.8 (ii). Cell-cell Communication- Key ConceptsHow cells in multi cellular organisms stick together and communicate?Extracellular material strengthens cells and helps bind them together.Cell-cell connections help adjacent cells adhere. Cell-cell gaps allow adjacent cells to communicate (cell adhesion and cell communication)Intercellular signals are responsible for creating an integrated whole from many thousands of independent parts.In target cells, intercellular signals are received, processed, responded to, and deactivated. If the signal is received at the cell surface, the processing step involves production of an intracellular signal.© 2011 Pearson Education, Inc.How Do Distant Cells Communicate? Cell Signaling and Communication The activities of cells, tissues, and organs in different parts of a multi-cellular organism are coordinated by long-distance signals.A signal transduction pathway is the series of amplification steps (molecular events) involved in a cell’s response to a signal  Only with membrane receptors.The cell membrane plays a key role in a cell’s response to environmental signals.© 2011 Pearson Education, Inc.•What Are Signals, and How Do Cells Respond to Them? • How Do Signal Receptors Initiate a Cellular Response?• How Is a Response to a Signal Transduced through the Cell?• How Do Cells Change in Response to Signals?To respond to a signal, a cell must have a specific receptor that can detect it.© 2011 Pearson Education, Inc.Hormones Are Long-Distance Messengers•Best-studied long distance signal molecules are the hormones. •A hormone is an information-carrying molecule that is secreted from a plant or animal cell, circulates in the body, and acts on target cells far from the signaling cell. •Although hormones are usually small molecules and are typically present in minute concentrations, they have a large impact on the condition of the organism as a whole. •The function and chemical structure of plant and animal hormones vary widely.© 2011 Pearson Education, Inc.Hormones Vary Widely in Effect and Structure•In addition to differences in their effects on their target proteins and chemical structure, hormones may be soluble or insoluble in lipids.–Lipid-soluble hormones usually diffuse across the plasma membrane into their target cells’ cytoplasm. Example:–Lipid-insoluble hormones are large or hydrophilic and do not cross the plasma membrane but instead bind to a receptor on the cell’s plasma membrane. Examples:© 2011 Pearson Education, Inc.© 2011 Pearson Education, Inc.•Step 1: Signal Reception  Receptor•Step 2: Signal Processing•Step 3: Signal Response•Step 4: Signal Deactivation© 2011 Pearson Education, Inc.Step 1: Signal Reception•Hormones and other cell-cell signals bind to signal receptors. –The presence of an appropriate receptor protein dictates which cells will be able to respond to a particular hormone. –All signal receptors are glyco-proteins–Signal + receptor  Binding favored[“knock on the door”]–Very specific binding reversible bindingIdentical receptors in diverse cells and tissues allow long-distance signals to coordinate the activities of cells throughout a multicellular organism. Most drugs that alter human behavior bind to specific receptors in the brain© 2011 Pearson Education, Inc.Signal Receptors•Signal receptors are proteins that change their shape or activity after binding to a signaling molecule.–Receptors are dynamic and may change in their sensitivity to particular hormones.–Receptors can be blocked. Signal receptors that bind to 1. lipid-soluble hormones are located inside the cell. 2. Most signal receptors are located in the plasma membrane  for polar signals© 2011 Pearson Education, Inc.The receptors for steroid hormones are located inside the cell, instead of on the membrane surface like most other signal receptors. Why is this not a problem for steroids?© 2011 Pearson Education, Inc.Step 2: Signal Processing•Lipid-soluble hormones that cross the plasma membrane produce different cell responses from lipid-insoluble hormones that bind to membrane receptors.Signal Processing in Lipid-Soluble HormonesLipid-soluble steroid hormones bind to receptors inside the cell and trigger a change in the cell’s activity directly. In this case the hormone-receptor complex is transported to the nucleus, where it alters gene expression.© 2011 Pearson Education, Inc.Signal Processing in Lipid-Insoluble Hormones•Hormones that cannot diffuse across the plasma membrane bind to membrane receptors. When a signal binds at the cell surface it triggers a complex series of events, collectively called a signal transduction pathway, which converts the extracellular hormone signal to an intracellular signal. RECEPTION, TRANSDUCTION, RESPONSE•The message transmitted by a hormone is amplified as it changes form. –Signal transduction occurs at the plasma membrane.–Amplification occurs inside.© 2011 Pearson Education, Inc.1. Ion channel2. G protein-linked receptors 3.Enzyme-linked receptors 3 types of membrane Receptors:© 2011 Pearson Education, Inc.How Do Signal Receptors Initiate a Cellular Response?3 Types (categories) of plasma membrane receptors (based on their activities) :–Ion channels (1)- example  acetylcholine–G protein-linked receptors (2)–Enzyme-linked receptors (3) A Gated Ion Channel (1)© 2011 Pearson Education, Inc.•Venom for black widow spider  Neurotoxin  causes explosive release of neurotransmitter, Acetylcholine  muscles unable to relax© 2011 Pearson Education, Inc.Signal Transduction•Signal transduction involves G protein receptors (2) or enzyme-linked