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Cell CommunicationChapter 6
• Cells communicate by signaling each other using chemical compounds such as neurotransmitters, hormones and other regulatory molecules.
• A signaling molecule binds to a receptor molecule on the cell surface or within the target cell
• Signal transduction: extracellular signal converted into an intracellular signal that causes dome changes in the cell.
• Cell Responds in a variety of ways (Channnels/Gates, Enzymes, Genes)
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All Living things require cell communication via chemical signals
Touch Upon in later units…• Prokaryotes: Quorum Sensing- critical concentration;
Biofilms- communities on a solid surface• Protists: Slime molds- Food scarcity; Secrete cAMP and form
multicellular colonies; Unicellular protist w/ similar protein signaling molecules
• Fungi:Similar signal pathways in yeasts/animals- importance to survival- minimal evolutionary changes
• Plants: Chemical defenses- resistance; volatile; predator insects attracted to decrease herbivorous insects
PRECISE INTERNAL COMMUNICATIONS AS WELL AS EFFECTIVE RESPONSES TO THE OUTSIDE ENVIRONMENT
WHY IS THIS NECESSARY??
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Homeostasis• The body has the ability to regulate its internal
environment (job of the Nervous and Endocrine systems) dynamic equilibrium
• Homeostasis involves regulating:– Blood levels of vital substances (Oxygen, glucose)– Heart rate and blood pressure– N-waste and removal– Body temperature– Rate and depth of breathing– etc
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SYSTEMS
SYSTEMS REQUIRE COMMUNICATION
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SYSTEMS REQUIRE COMMUNICATION
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1. Send a Signal Chemically synthesize/release2. Reception Target Cell- close or far away 3. Transduction Extracellular to Intracellular4. Response ; Activate or Inhibit
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1. The Signal
*Change in:• Cell division• Cell shape
• PERMEABILITY• Cell growth
• METABOLISM• Cell differentiation
**PROTEIN/ENZYME
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*T cell antigen
stimulation of
growth factors
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*Nitrous Oxide
and Blood Vessel
Dilation
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“Classic” endocrine signaling
Hormones -transported by the blood (some dissolved in plasma, some bound to proteins) and produce a response only after they reach target cells and bind with specific receptors. Target cells- another endocrine gland or another organ. Hormones are removed from the blood by the liver (inactivates) and by the kidney (secretes).
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“Local Regulators vs Endocrine”
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• Large proteins or glycoproteins• Bind with specific signaling molecules (Ligands)
-Most are Hydrophilic; bind to surface receptors -Some are small, hydrophobic and diffuse through the cell
membrane and bind with intracellular receptors “Transcription Factors”- Gene Expression *Steroid hormones; Vits A, D, NO
-HIGHLY Selective; May differ during different stages of cell life cycle, or in response to different conditions
-Same signal can have different meanings for different target cells.
-May respond to signals other than chemical (ex-light)-Receptors can be Down-regulated or Up-regulated, depending
on the needs of the cell (Ex- insulin receptors stimulate cells to take in glucose…not needed, destroy receptors via lysosomes)
2. The Reception
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EXTRACELLULAR (CELL-SURFACE) vs
INTRACELLULARRECEPTORS
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Types of cell Surface Receptors
“Ligand-Gated Channels”Convert Chemical to ElectricalNeurotransmitter, or ion inside*Muscle contraction
Trans Membrane Proteins-Outer part binds to the ligand, cytosol part binds to a specific G protein, changing its shape 60% of meds
Trans membrane; binding site outside; enzyme component or binding site inside*Kinases, ethylene (germ,ripening)
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3. Signal Transduction• MANY regulatory molecules transmit info to the interior
without crossing the cell membrane. Membrane proteins transduce the signal, and the signal is AMPLIFIED
• Each part is a ‘relay switch’ ON or OFF• First component- the receptor (transmembrane or
intracellular)- conformational shape change with ligand• Signal is then relayed through a sequence of proteins• *Second Messengers- intracellular agents “Signaling
Cascade” cAMP cyclic AMP Calcium ions
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Second Messenger Systems
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Hormones that work through secondary messengers
Text p 1035 Fig 48-5
1. First messenger (ligand) binds a cell surface receptor (membrane protein) 2-3. Creates a series of membrane-bound reactions to activate an effector (G-protein-relay-enzyme)4. Generates/activates the second messenger molecule- cAMP )
5.
Signal Transduction Pathways 9.24