Cell signaling

Question 1

how is communication bw cells mediated?

Answer 1

by extracellular signal molecules

Question 2

what does reception of signal depend on? in what 3 places can these be located?

Answer 2

receptor proteins; on cell surface, within cell or on cell nuclear membrane

Question 3

what happens when a signal is bound?

Answer 3

first activates receptor, then signal pathway is activated

Question 4

how is intracellular signaling done?

Answer 4

intracellular signaling proteins process signals, then effector proteins target changes in cell behavior

Question 5

what is an effector protein’s role in intracellular signaling? what are 5 examples?

Answer 5

it transmits signal throughout the cell; gene regulatory proteins, enzymes, ion channel proteins, parts of a metabolic pathway, or cytoskeletal proteins

Question 6

what can be extracellular signals? give 4 examples

Answer 6

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

Question 7

what do extracellular signals do?

Answer 7

bind specific receptors on cell surface (transmembrane proteins) or other places in a cell (like intracellular)

Question 8

what are the 2 types of extracellular signals? how are they different?

Answer 8

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)

Question 9

when is contact dependent signaling used?

Answer 9

during development and immune response

Question 10

what is another type of paracrine signaling? how is it used?

Answer 10

autocrine signals - cells produce signals that they respond to themselves; used in cancer cells (promote growth/ inhibit activity)

Question 11

are signaling cells and targets are the same type of cells?

Answer 11

No, they’re different

Question 12

what are the two types of long-range signaling?

Answer 12

synaptic and endocrine

Question 13

explain how synaptic signalers are used. where are these seen?

Answer 13

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

Question 14

explain how endocrine signalers work.

Answer 14

Hormonal system cells synthesize and release chemical (protein, steroid, amine-derived) hormones into bloodstream to affect distant targets

Question 15

how does the idea of signal integration work?

Answer 15

Cells must integrate and respond to multiple signals to provide the appropriate action at the appropriate time; No signal, no receptor = cell death

Question 16

do all cells respond the same to the same signal? what does this depend on?

Answer 16

No, different cell types respond to the same signal differently; dependent on internal signals, effectors and genes

Question 17

what are the three classes of cell-surface receptors?

Answer 17

ion-channel coupled, G-protein-coupled receptors (GPCR), enzyme-coupled receptors

Question 18

what are ion-channel coupled receptors aka? what transmits the signal? how does the receptor react? how is it coupled?

Answer 18

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

Question 19

how do G-protein-coupled receptors work? what can work as a target here? where is this found?

Answer 19

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

Question 20

how do enzyme-coupled receptors work?

Answer 20

can act as enzymes themselves once activated or associate and activate with enzymes intracellularly

Question 21

Explain the signaling process and the role of intracellular signaling proteins play.

Answer 21

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.

Question 22

what are examples of second messenger signals?

Answer 22

cAMP, calcium, or diacylglycerol

Question 23

what are examples of intracellular responses induced by intracellular signaling proteins? are these responses reversible?

Answer 23

GTP binding, phosphorylation via kinases, removal of phosphate by phosphatases, altered protein conformation; yes

Question 24

how can a cell respond to extracellular signals? what does it depend on?

Answer 24

fast or slow, depends on mechanism of delivery, nature of response and turnover of signals

Question 25

what factors indicate the speed at which a cell will respond to extracellular signal?

Answer 25

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

Question 26

what type of receptors are used by all eukaryotes? what makes them special? what are they structured?

Answer 26

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

Question 27

in what areas do GPCRs function?

Answer 27

sensation, neurotransmission, endocrine system, cell communication such as drug and external world signaling

Question 28

what are G-proteins? what is their role in signaling? are these specific?

Answer 28

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

Question 29

what is G-protein composed of? how do the constituents work?

Answer 29

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

Question 30

how can G-proteins effect cell signaling? why? what effect does this have?

Answer 30

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

Question 31

how do hydrophobic signal molecules work? examples?

Answer 31

move directly across the cell membrane; These include steroid hormones, fat soluble vitamins, thyroid hormones

Question 32

what is the function of hydrophobic signal molecules?

Answer 32

bind to intracellular receptor proteins which then control transcription; all of these belong to a “superfamily”; transcriptional response takes multiple steps

Question 33

Most diseases are the result of cell communication breakdown, give 4 examples with example of disease

Answer 33

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

Question 34

what are two examples of diseases with multiple signaling breakdowns?

Answer 34

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.