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Cell Communication AP Biology The “Cellular Internet” • Biologists have discovered some universal mechanisms of cellular regulation that involve cell-to-cell communication. •External signals are converted into responses within the cell Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Methods used by Cells to Communicate • Cell-Cell communication • Cell Signaling using chemical messengers 1. Local signaling over short distances • Cell-Cell Recognition • Local regulators – Paracrine (growth factors) – Synaptic (neurotransmitters) 2. Long distance signaling • Hormones Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cell-Cell Communication • Animal and plant cells – Have cell junctions that directly connect the cytoplasm of adjacent cells Plasma membranes Gap junctions between animal cells Plasmodesmata between plant cells Figure 11.3 (a) Cell junctions. Both animals and plants have cell junctions that allow molecules to pass readily between adjacent cells without crossing plasma membranes. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cell-Cell Communication Animal cells use gap junctions to send signals Cells must be in direct contact Protein channels connecting two adjoining cells Gap junctions between animal cells AP Biology Cell-Cell Communication Plant cells use plasmodesmata to send signals Cells must be in direct contact Gaps in the cell wall connecting the two adjoining cells together Plasmodesmata between plant cells AP Biology Local Signaling: Cell-Cell Recognition • In local signaling, animal cells may communicate via direct contact • Membrane bound cell surface molecules • Glycoproteins • Glyolipids Figure 11.3(b) Cell-cell recognition. Two cells in an animal may communicate by interaction between molecules protruding from their surfaces. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Local Signaling: Local Regulators • In other cases, animal cells – Communicate using local regulators – Only work over a short distance Local signaling Target cell Electrical signal along nerve cell triggers release of neurotransmitter Neurotransmitter diffuses across synapse Secretory vesicle Local regulator diffuses through extracellular fluid (a) Paracrine signaling. A secreting cell acts on nearby target cells by discharging molecules of a local regulator (a growth factor, for example) into the extracellular fluid. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Target cell is stimulated (b) Synaptic signaling. A nerve cell releases neurotransmitter molecules into a synapse, stimulating the target cell. Long-distance Signaling: Hormones • In long-distance signaling – Both plants and animals use hormones Long-distance signaling Endocrine cell Blood vessel Hormone travels in bloodstream to target cells Target cell Figure 11.4 (c) Hormonal signaling. Specialized endocrine cells secrete hormones into body fluids, often the blood. Hormones may reach virtually all C body cells. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Long-Distance Signaling Nervous System in Animals Electrical signals through neurons Endocrine System in Animals Uses hormones to transmit messages over long distances Plants also use hormones Some transported through vascular system Others are released into the air AP Biology The Three Stages of Cell Signaling • Earl W. Sutherland (1971) – Discovered how the hormone epinephrine acts on cells • Sutherland suggested that cells receiving signals went through three processes – Reception – Transduction – Response • Called Signal transduction pathways – Convert signals on a cell’s surface into cellular responses – Are similar in microbes and mammals, suggesting an early origin Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Overview of cell signaling EXTRACELLULAR FLUID 1 Reception CYTOPLASM Plasma membrane 2 Transduction 3 Response Receptor Activation of cellular response Relay molecules in a signal transduction pathway Signal molecule Figure 11.5 Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Three Stages of Cell Signaling EXTRACELLULAR FLUID CYTOPLASM Plasma membrane 1 Reception Receptor The receptor and signaling molecules fit together (lock and key model, induced fit model, just like enzymes!) Signaling molecule Signaling molecule binds to the receptor protein AP Biology Three Stages of Cell Signaling CYTOPLASM EXTRACELLULAR FLUID Plasma membrane 1 Reception 2 Transduction Receptor 2nd Messenger! Relay molecules in a signal transduction pathway Signaling molecule The signal is converted into a form that can produce a cellular response AP Biology Three Stages of Cell Signaling CYTOPLASM EXTRACELLULAR FLUID Plasma membrane 1 Reception 2 Transduction 3 Response Receptor Activation of cellular response Relay molecules in a signal transduction pathway Signaling molecule Can be catalysis, activation of a gene, triggering apoptosis, almost anything! The transduced signal triggers a cellular response AP Biology Signal Transduction Animation http://media.pearsoncmg.com/bc/bc_ campbell_biology_7/media/interactiv emedia/activities/load.html?11&A http://www.wiley.com/legacy/college/bo yer/0470003790/animations/signal_tran sduction/signal_transduction.htm AP Biology Calcium ions and Inositol Triphosphate (IP3) • Calcium, when released into the cytosol of a cell acts as a second messenger in many different pathways Calcium is an important EXTRACELLULAR FLUID ATP Plasma membrane Ca2+ pump Mitochondrion second messenger because cells are able to regulate its concentration in the cytosol Nucleus CYTOSOL Ca2+ pump ATP Key Ca2+ pump Endoplasmic reticulum (ER) High [Ca2+] Low [Ca2+] Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Other second messengers such as inositol triphosphate and diacylglycerol can trigger an increase in calcium in the cytosol Growth factor 3. Response Receptor Reception Many possible outcomes This example shows a transcription response Phosphorylation cascade CYTOPLASM Inactive transcription factor Active transcription factor P DNA Gene NUCLEUS mRNA AP Biology Transduction Response Signaling molecule Specificity of the Receptor signal The same signal molecule can trigger different responses Many responses can come from one signal! Relay molecules Response 1 Response 2 Response 3 Cell A. Pathway leads Cell B. Pathway branches, to a single response. leading to two responses. AP Biology The signal can also trigger an activator or inhibitor The signal can also trigger multiple receptors and different responses Activation or inhibition Response 4 Response 5 Cell C. Cross-talk occurs Cell D. Different receptor between two pathways. leads to a different response. AP Biology REVIEW: Signal-transduction pathway Definition: Signal on a cell’s surface is converted into a specific cellular response Local signaling (short distance): √ Paracrine (growth factors) √ Synaptic (neurotransmitters) Long distance: hormones AP Biology Stages of cell signaling 3 steps: •Reception: target cell detection •Transduction: single-step or series of changes •Response: triggering of a specific cellular response AP Biology The three stage of cellular signaling: Reception, Transduction, and Response. http://media.pearsoncmg.com/bc/bc_campbell_biology_7/media/interactivemedia/activities/load.html?11&A AP Biology Tight junction AP Biology Desmosome junction AP Biology
