Cell Communication Chapter 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)

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??

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

SYSTEMSSYSTEMS SYSTEMS REQUIRE COMMUNICATION

1.Send a Signal Chemically synthesize/release 2.Reception Target Cell- close or far away 3.Transduction Extracellular to Intracellular 4.Response ; Activate or Inhibit

1. The Signal *Change in: Cell division Cell shape PERMEABILITY Cell growth METABOLISM Cell differentiation **PROTEIN/ENZYME

*T cell antigen stimulation of growth factors

*Nitrous Oxide and Blood Vessel Dilation

“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).

“Local Regulators vs Endocrine”

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

EXTRACELLULAR (CELL-SURFACE) vs INTRACELLULAR RECEPTORS

Types of cell Surface Receptors “Ligand-Gated Channels” Convert Chemical to Electrical Neurotransmitter, 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)

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

Second Messenger Systems

Hormones that work through secondary messengers Text p 1035 Fig 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