cell communication Flashcards
direct cell communication
direct exchange of materials between the cytoplasm (gap junctions, plasmodesmata) (touching!); direct interaction of cell surface molecules (touching!)
indirect cell communication
indirect communication between two non-contacting cells using a signal released from one cell that affects the function of a second; different types of signaling systems that are based on the distance that separates the 2 cell types or nature of signal
paracrine signaling
the release of a chemical signal from one cell that is detected by and alters the function of a CLOSELY located cells
autocrine signaling
the release of a chemical signal from one cell that is detected by and alters the function of the SAME CELL, specialized signaling mechanism that allows the signaling cell to monitor the amount of signal that is being released
neural signaling
synaptic signaling, over short distance between neurons, synapse between cells, neurotransmitters diffuse across synapse
endocrine
long distance (hormonal) signaling, signaling aka hormone put into blood stream
whaat types of molecules can act as signals? (4)
amino acids (glutamic acid excitatory neurotransmitter), amino acid derivatives (GABA glutamic acid, major inhibitory neurotransmitter, Epinephrine tyrosine, hormone that increases blood glucose), steroids (estrogen, glucocorticoids), peptides and proteins (insulin, glucaogon), gases (nitric oxide, vasodilator)
receptor specificity
signals (ligands) cannot alter cell function until binded to receptor SPECIFIC
receptor types
inside membrane and cytoplasm
membrane receptors
interact with hydrophilic signals that cannot cross the plasma membrane, amino acids, their derivatives, peptides
cytoplasmic receptors
bind to hydrophobic signals that can cross plasma membrane, steroids
3 stages of signaling process in target cell
reception, transductions, response
reception
ligand binds to receptor and changes cell function
transduction
cell signal being amplified
response (2)
activation of cellular responses: alteration of enzyme function or alteration of gene expression
signal transduction pathways
cascades of intracellular events, triggered by the binding of ligand to specific receptor, ligand binding activates series of KINASE enzymes
kinase
enzyme that add a phosphate group onto another molecule usually a protein and often another enzymes
kinase chain and phosphate group
the phosphate group will change the shape of the protein and alter its function, leads to enzyme activation, phosphatase reduce enzymatic activity
switches! with kinase & phosphatase
phosphate groups are switches activated by kinases, phosphate groups are removed/turned off by phosphatase
3 advantages to cascade of signal / structure of cell signaling pathway
signal is amplified, allows one signal to diverge and control a whole range of cellular processes, allows other signals to control cascade
second messangers function
act to trigger the transduction cascade, intracellular concentrations are controlled by receptor activation, function as intermediaries between the receptor and cascade
3 principal second messangers
cyclic AMP, calcium ions, inositol triphosphate
cyclic AMP structre !!!!!
adenosine triphosphate and ribose, has ATP, cyclic through pyrophosphate (cycle) and phosphodiesterase (decycle)
transmembrane receptors 3
G-linked receptors (epinephrine receptor), tyrosine-kinase receptor (insulin), ligand gated receptor, (calcium channels)
G-linked protein receptors
linked to relay proteins that bind guanosine di- and triphospahte (GDP, GTP)
G-linked protein receptor pathway
ligand binds, G-protein can now bind to receptor, GDP replaced by GTP, allows the G-protein to move along membrane to adjacent enzyme to inhibit or activate it, GTP on G-protein is the hydrolyzed back to GDP and G-protein is deactivated (ligand dissociates)
g-protein linked receptors shape
lots of alpha helices, cholesterol, molecule mimicking ligands, signal binding site has to have ligand inserted correctly, 7 alpha helices (hydrophobic amino acids) in structure, N-terminus outside, C-terminus on inside of cell,
adenylyl cylase
allows synthesis of cyclic AMP
activity of cyclic AMP depends on
adenylyl cyclase and G protein activity
protein kinase A
top level of transduction pathway, catalyze addition of phosphate group to kinases
epinephrine reception
epinephrine binds to G-protein coupled receptor
epinephrine transduction
10^2 active G protein, 10^2 adenylyl cyclase, 10^4 cyclic AMP, active protein kinase A 10^4, phosphorylase kinase 10^5, glycogen phosphorylase 10^6 (active molecules increase and amplify;
epinephrine response
glycogen activates glucose 1-phosphate (10^8) molecules, increases glucose in the blood stream
tyrosine kinse recpetors
transmembrane receptors, have 2 components: a kinase and target/relay protein that’s separate from receptor
tyrosine kinase receptor ligand binding
has two parts, which dimerize when ligand binds, dimerization activates the kinase part of receptor
tyrosine kinse pathway
after ligand binds and kinase is activated, kinase moves phosphate group from ATP to a specific amino acid (tyrosine, serine, or threonine) located iwthin the cytoplasmic part of the receptors polypeptide chain, protein kinase receptor (auto)phosphorylates itself, which then activate rely proteins by phosphorylation
insulin receptor
tyrosine kinase receptor, consists of two monomers, each has a beta and alpha (where binding happens) subunit
insulin receptor pathway
two molecules of insulin bind to receptor, when insulin binds to alpha subunit, receptor dimerizes, activates protein kinase in the beta subunit of receptor, autophosphorylates, insulin receptors target and phosphorylate other cytoplasmic proteins call insulin response substrates, (LOWERS GLUCOSE), control insertion of glucose transporters into the membrane
glucose transporter molecules (GLUT4)
are activated and inserted in cell membrane due to insulin receptor pathway
activation of gene expression by kinase signaling cascades
response activates or deactivates transcription factor on DNA and genes in nucleus, (by phosphorylation cascade in cytoplasm to nucleus, a kinase moves into nucleus and activate transcription factor)
calcium as second messenger
can activate a larger number of different signaling and cellular proteins, concentration of calcium is carefully controlled inside cell (can be very less than outside the cell), abrupt increases cause series of cellular events
calmodulin
calcium binds to this, an abundant intracellular protein, which is a kinse that can trigger a calcium dependent protein kinase cascade
2 ways of calcium increase intracellularly
facilitated diffusion through ion channels (gates), the release of calcium from intracellular store (smooth ER) by signal transduction cascade that uses inositol trisphosphate (IP3)
signal transduction cascade that uses inositol trisphosphate (IP3) activation (2)
either G-protein linked receptors not linked to cAAMP or protein kinase receptors like the insulin receptor
phospholipse C function
cleaves PIP2 into two parts, one that stays in membrane and one that goes into cytoplasm (activated by G-protein or tyrosine kinase)
PIP2 structure (IP3 made by cleaveage)
ester linkage, fatty acid tail, glycerol, and has. molecule linked to cyclic carbon ring (3 phosphates) and one links to glycerol
IP3 function
binds to calcium channel and opens it to allow calcium out, which then goes to calmodulin and cellular response
terminate calcium signal
calcium pumps remove calcium from the cytoplasm, use ATP to move Ca2+ againt concentration gradient; pumped into: out of cell, mitochondria, into smooth ER)
diversity in cell signaling (3)
pathway leads to signal response, pathway branches, leading to two responses, cross-talking (interactions between different cascades) occurs between two pathways (IP3 example); different receptor leads to a different response becaus target cells have different responses (serotonin receptors)
steroid receptors
use intracellular (cytoplasmic) receptors to control: gene expression, other intracellular signaling pathways (cross talk)
