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CELL COMMUNICATION (Methods of Cell Communication (Local Communication …
CELL COMMUNICATION
Methods of Cell Communication
Local Communication :house_buildings:
Paracrine
Signaling: chemical acts on cell in the immediate viscinity
Autocrine
Signaling: chemical acts on cell that secreted it
Contact Dependent Signaling :silhouettes:
surface molecules on each cell bind to each other
Long Distance Signaling :telephone_receiver:
Hormones [secreted into blood and binds to cells that have receptor for hormones]
Gap Junctions :bridge_at_night::
direct transfer of chemical signals through cytoplasmic bridges
Modulators of Cell Signaling
Receptors (NOT the ligand) are the major modulators.
Specificity (receptors bind specific ligands)
Competition (diff ligands can bind to same receptor, the one w higher affinity will bind most)
Mult. receptors for 1 ligand
When the same ligand binds to a diff receptor, it results in a diff response
Ex. Epinephrine binds to alpha-receptor (vessel constricts) OR beta-receptor (vessel dilates)
Receptor up & down regulation
too much ligand- cell down regulates receptors (moved from membrane via endocytosis) ex. drug tolerance
too little ligand- cell up regulates receptors (damaged cell releasing ligands) timed development
Receptors are good for pharmacologists
beta-blockers (anxiety antagonist)
inhibit normal epinephrine-mediated sympathetic actions
reduces the effect of excitement/physical exertion on heart rate and force of contraction & dilation of blood vessels
H2 antagonists (acid reflux)
block the receptor for histamine & thereby prevent histamine from stimulating acid-producing cells
CELL SIGNALING :signal_strength:
Receptors
(made of proteins) facilitate specific cellular responses.
locations
Cytosol {Sm. lipophilic molecules that go inside}
Nucleus
Cell Membrane {lrg. lipophobic signal molecules}
TYPES
Ligand-gated channels
(receptor channels) ball & chain, opens or closes an ion channel
Receptor-enzymes
(activate intracellular enzymes)
G Protein-coupled receptors
(activate intracellular second messengers
FIRST MESSENGERS
(signal molecules/ ligands)
Lipophillic, Hydrophobic, Nonpolar
Small (can go inside)
Lipophobic, Hydrophilic, Polar
Large (can't go inside...BIND TO CELL MEM RECEPTORS)
SECOND MESSENGERS SYSTEMS
(Several diff types, similar in overall mech, vary in substances involved and effects produced)
allow for signal transduction....conversion of extracellular message into intracellular message that leads to a response
allows for signal amplification (creates larger physiological effect)
intracellular signaling molecules that trigger physiological changes (eg. cAMP, cGMP, IP3, DAG, Ca++
Physiological Changes
: proliferation, differentiation, migration, survival, and apoptosis
PLAYERS IN SINGAL TRANSDUCTION 2nd MESSENGER SYSTEM:
Outside Cell
ECF signal molecule (1st messenger)
Receptor/ Signal Transducer (eg. G Protein)
Inside Cell
Primary
Effector
(amplifier)
amplifies a single by activating more molecules
e.g. Adenylyl cyclase, gunnel cyclase, phospholipase C (
PLC
)
Second Messenger
KINASES
phosphorylates proteins
phosphatases (removes P) from proteins
eg.
DAG
, cAMP, cGMP, IP3
Secondary Effector
e.g.. PKA, PKC, CaM, Ca++
G PROTEIN COUPLED RECEPTORS (GPCRs)
Has 7
transmembrane spanning regions
:snake:
G Protein
(transducer) 3 subunits alpha, beta, gamma
Activated by
GTP
or
GDP
PHOSPHOLIPASE C SYSTEM
(G-protein coupled 2nd messenger system)
Key Players
Diacylglycerol (DAG) secondary messenger
Inocytol triphosphate (IP3) also secondary messenger
Phospholipase C (PLC) primary effector amplifier
Ca++ :arrow_right: enters cytoplasm from E.R. and/or ECF via
VOLTAGE GATED CHANELS or LIGAND GATED CHANNELS
(secondary effector)
Protein Kinase C (PKC) (also secondary effector)
:large_blue_diamond: Signal molecule activates G Protein coupled receptor
:large_blue_diamond: G Protein activates
PLC
:large_blue_diamond:
PLC
converts a membrane phospholipid into
2
second messengers (
DAG
&
IP3
)
:large_blue_diamond:
DAG
phosphorylates
PKC
which phosphorylates a protein which carries out response :tada:
:large_blue_diamond:
IP3
enters the cytoplasm & binds to a Ca++ channel on the E.R., which opens to release Ca++ into the cytosol which leads to a cellular response :tada:
Types of Physiological Signals
CHEMICAL SIGNALS :female-scientist::skin-tone-5: (Responsible for most cell communication. Chemicals/Ligands are secreted by cells into EC. Target Cells have receptors that bind ligands)
ELECTRICAL SIGNALS :zap: (Changes in membrane potential)