Cell signaling Flashcards
how is communication bw cells mediated?
by extracellular signal molecules
what does reception of signal depend on? in what 3 places can these be located?
receptor proteins; on cell surface, within cell or on cell nuclear membrane
what happens when a signal is bound?
first activates receptor, then signal pathway is activated
how is intracellular signaling done?
intracellular signaling proteins process signals, then effector proteins target changes in cell behavior
what is an effector protein’s role in intracellular signaling? what are 5 examples?
it transmits signal throughout the cell; gene regulatory proteins, enzymes, ion channel proteins, parts of a metabolic pathway, or cytoskeletal proteins
what can be extracellular signals? give 4 examples
Either membrane bound molecules (need direct contact with target) or are released into extracellular space by exocytosis or diffusion; Proteins, Amino acids, Steroids, steroid hormones, Nitric oxide
what do extracellular signals do?
bind specific receptors on cell surface (transmembrane proteins) or other places in a cell (like intracellular)
what are the 2 types of extracellular signals? how are they different?
contact dependent signaling - signal remains attached to cell surface receptor of the signaling cell and influences only those cells it contacts (not released, remain connected); paracrine signaling - signals (local mediators) are released but affect only targets in the vicinity (released into extra matrix)
when is contact dependent signaling used?
during development and immune response
what is another type of paracrine signaling? how is it used?
autocrine signals - cells produce signals that they respond to themselves; used in cancer cells (promote growth/ inhibit activity)
are signaling cells and targets are the same type of cells?
No, they’re different
what are the two types of long-range signaling?
synaptic and endocrine
explain how synaptic signalers are used. where are these seen?
Nervous system neurons with long axons release chemical neurotransmitters onto post-synaptic sites (synapse is the locale of release); these sites then have an electrical reaction (action potential) based upon the type of neurotransmitter binding to the post-synaptic receptors; in muscles
explain how endocrine signalers work.
Hormonal system cells synthesize and release chemical (protein, steroid, amine-derived) hormones into bloodstream to affect distant targets
how does the idea of signal integration work?
Cells must integrate and respond to multiple signals to provide the appropriate action at the appropriate time; No signal, no receptor = cell death
do all cells respond the same to the same signal? what does this depend on?
No, different cell types respond to the same signal differently; dependent on internal signals, effectors and genes
what are the three classes of cell-surface receptors?
ion-channel coupled, G-protein-coupled receptors (GPCR), enzyme-coupled receptors
what are ion-channel coupled receptors aka? what transmits the signal? how does the receptor react? how is it coupled?
aka ionotropic or transmitter-gated; rapid signals mediated by neurotransmitters that open or close ion channels based on excitation or inhibition of the post-synaptic target; ion channel is coupled to a transmembrane protein
how do G-protein-coupled receptors work? what can work as a target here? where is this found?
signal activates receptor and GTP-binding protein (G-protein) which in turn activates the target; Targets can be enzymes, other proteins, ion channels; the G-protein subunits is attached to cytosolic lipid bilayer with an anchor
how do enzyme-coupled receptors work?
can act as enzymes themselves once activated or associate and activate with enzymes intracellularly
Explain the signaling process and the role of intracellular signaling proteins play.
Once an extracellular signal has bound to a cell membrane receptor, a second message is sent within the cell; the second messenger signal passes along the signal to effectors; effectors work as an on or off switch; which creates and intracellular response using intracellular signaling proteins.
what are examples of second messenger signals?
cAMP, calcium, or diacylglycerol
what are examples of intracellular responses induced by intracellular signaling proteins? are these responses reversible?
GTP binding, phosphorylation via kinases, removal of phosphate by phosphatases, altered protein conformation; yes
how can a cell respond to extracellular signals? what does it depend on?
fast or slow, depends on mechanism of delivery, nature of response and turnover of signals
what factors indicate the speed at which a cell will respond to extracellular signal?
Fast response: if changes occur to proteins already present within cell; altered protein function
Slow response: if changes to gene expression or new protein synthesis are required; altered protein synthesis
what type of receptors are used by all eukaryotes? what makes them special? what are they structured?
G-Protein-Coupled Cell-Surface Receptors (GPCRs); the largest family of cell surface receptors; polypeptide with several transmembrane domains and all use G proteins to signal cell interior
in what areas do GPCRs function?
sensation, neurotransmission, endocrine system, cell communication such as drug and external world signaling
what are G-proteins? what is their role in signaling? are these specific?
trimeric GTP-binding proteins attached to cytoplasmic face of cell membrane; Couples the receptor to either enzymes or ion channels; When signal binds to GPCR, the receptor activates the G protein; G proteins are specific for sets of GPCRs and a particular set of target proteins
what is G-protein composed of? how do the constituents work?
3 subunits: α, β and γ; α (a GTPase) binds GDP and keeps G protein inactive but then releases GDP and binds GTP which activates G protein
how can G-proteins effect cell signaling? why? what effect does this have?
considered to be stimulatory or inhibitory based on the activation of adenylyl cyclase (increases cAMP) or inhibition (decreases cAMP) of it; Adenylyl cyclase synthesizes cAMP which is how some extracellular signals work to mediate a cellular response
how do hydrophobic signal molecules work? examples?
move directly across the cell membrane; These include steroid hormones, fat soluble vitamins, thyroid hormones
what is the function of hydrophobic signal molecules?
bind to intracellular receptor proteins which then control transcription; all of these belong to a “superfamily”; transcriptional response takes multiple steps
Most diseases are the result of cell communication breakdown, give 4 examples with example of disease
lost signals (diabetes I), Cell signal does not reach target (multiple sclerosis), Target cell does not respond (diabetes II), too much signal (stroke w release of glutamate in brain
what are two examples of diseases with multiple signaling breakdowns?
cancers - with cell growth and division despite absence of signal and loss of self-destruction; other new signals allow angiogenesis; Dysregulation of leukocyte adhesion and endothelial cell interaction - contributes to cancer, vascular occlusion in sickle cell, sepsis, etc.
