BSI Lecture 15-16 Cell Signaling Flashcards
What do secretory cells release that are recognized by SPECIFIC receptors?
Chemical messengers
Many pharmaceutical drugs target specific __________
Receptors
Chemical messengers sent throughout the body via circulation is _________
Endocrine
Chemical messengers that act locally on adjacent cells is _______
Paracrine
Chemical messengers acting on the cell that secreted it is _____
Autocrine
Chemical messengers released across a synapse from a neuron is _________
Neurotransmitter
Neurotransmitters across a synapses can affect neurons or “effectors” such as ______ or ______.
Muscles; glands
Chemical messengers that are never released but requires physical contact is ____________.
Contact dependent
Chemical messengers can affect every aspect of a cell function such as (5 of them)
1) Growth
2) Differentiation
3) Metabolism
4) Processing of data
5) Programmed cell death
In order for a cell to survive, a cell needs to be receiving a signal from ______ ______
Growth factors
T or F? Cells in the body are subject to only ONE messenger at a time.
False, usually cells are subject to a “cocktail” of different messengers
Most chemical messengers cannot cross the cell membrane so they must be recognized by a specific cell surface receptor: binding the correct messenger causes a conformational change in the receptor, a protein, which is then transmitted intracellularly. This is called what?
Signal transduction
After signal transduction, “activated” receptor then affects various ______ _________ to produce its desired response.
Signaling pathways
Which of Dr. Wrights’ mechanisms require extracellular recognition of the signaling molecule.
Mechanisms 1, 2, and 3
Name the 5 main components in a typical signal transduction?
1) Extracellular signal molecule
2) Receptor proteins
3) Intracellular signaling molecules
4) Effector proteins
5) Cell responses
______ _______ are molecules produced inside the cell that causes a response.
Secondary messengers
Calcium, cyclic adenosine monophosphate (cAMP), cyclic guanosine monophosphate (cGMP) are examples of what?
Secondary messengers
T or F? Calcium is produced and acts as a secondary messenger.
False, calcium is released not produced
_________ stage increase the signals throughout the cell; turns 1 signal into a million products.
Amplification
T or F? Kinases phosphorolates a specific protein after being activated by a specific pathway.
True
T or F? Kinase phosphorolates a target protein, turning them on.
False, it can either turn it on or off
T or F? Signal transduction is a linear path?
False
What kind of chemical messengers are able to cross the cell membrane and what are they recognize by?
Hydrophobic molecules; Intracellular receptors (or enzymes)
Aldosterone, Cortisol, Testosterone are examples of _____ hormones.
Steroid
Thyroxine (T4) and Triiodothyronine (T3) are examples of ___ hormones.
Thyroid
Nitric oxide* (NO), Carbon Monoxide (CO) and examples of the _____ ______ messengers.
Novel gaseous
______ is specific protein in either the plasma membrane or interior of a target cell that a messenger combines with.
Receptor
_____ is the ability of a receptor to bind only one type or a limited number of structurally related types of chemical messengers
Specificity
____ is the degree to which receptors are occupied by messengers.
Saturation. If all are occupied it’s 100% saturated. If half are occupied it’s 50% saturated.
____ is the strength with which a chemical messenger binds to its receptor.
Affinity
____ is the ability of different molecules that are very similar in structure to compete with each other to combine with the same receptor.
Competition
____ is a chemical messenger that binds to a receptor and triggers the cell’s response; often refers to a drug that mimics a normal messenger’s action.
Agonist
_____ is a decrease in the total number of target-cell receptors for a given messenger; may occur in response to chronic high extracellular concentration of the messenger.
Down-regulation
_____ is an increase in the total number of target-cell receptors for a given messenger; may occur in response to chronic low extracellular concentration of the messenger.
Up-regulation
_____ is the increased responsiveness of a target cell to a given messenger; may result from up-regulation of receptors.
Supersensitivity
Mechanism 1 is the simplest as the specific cell surface receptor is also a(n) _____ ______.
Ion channel
Mech 1: Upon binding the messenger, the ion channel normally ______ but may ______ them.
Opens; close
Sometimes calcium (Ca2+) enters a cell through Mech 1, and binds to, activate, specific calcium binding proteins intracellularly, (such as Calmodulin). Calcium is acting as a ______ ______
Secondary messenger
The best example of an _____ _____ is the Nicotinic Acetylcholine Receptor (nAChR) found at neuromuscular junctions, (skeletal muscle), autonomic ganglia and in the brain.
Ionotropic receptor
What are the 2 classes acetylcholine receptors?
Nicotinic and Muscarinic
Protein recap: If molecule A and molecule B are poorly matched and have only a few week bonds between them, what rapidly breaks them apart?
Thermal motion
Does metabotropic receptors affect membrane potential directly?
No, ionotropic receptors do
Do ionotropic receptors utilize g-proteins or significant signal transduction pathways?
No, metabotropic receptors do
__________ receptors are indirectly linked to protein channels.
Metabotropic
T or F? Mech 1 (ionotropic receptor) does not cause a change in membrane potential.
False
Can 2 proteins interact and affect their activities?
Yes
_______ are receptors which activate heterotrimeric G-proteins intracellularly after binding the messenger extracellularly.
GPR (G protein coupled receptors)
______ are receptors which dimerize and phosphorylate each other (intracellularly) after binding the specific messenger (extracellularly); they either directly activate kinase cascades or act via low molecular weight G-proteins.
Receptor Tyrosine Kinases (RTKs)
_______ are sites of signal transduction pathway integration and regulation; these pathways are not linear and cross-talk extensively.
G-proteins
________________ have 3 subunits and are self-limiting (on a timer), are activated by GPR’s
Heterotrimeric G-proteins
What are the 2 types of G-Proteins?
Heterotrimeric and Low Molecular Weight
____________ (also called monomeric) have one subunit and need accessory proteins to turn them off. These need RTK’s plus additional accessory proteins to be activated.
Low molecular weight G-proteins
Why are G-proteins called G-proteins?
Because they bind guanosine nucleotides; both LMW G-proteins and the alpha-subunit of heterotrimerics bind GDP when inactive and GTP when activated.
What is a secondary messenger?
A small molecule such as cAMP which is produced intracellularly in response to a messenger and diffuses across the cell affecting target proteins such as enzymes and ion channels.
What is a GEF?
A Guanosine Exchange Factor; this is the activated GPR for heterotrimerics and the dimerized (so active) RTK’s c/w other proteins AND the specific GEF. As the name suggests, these allow the exchange of bound GDP (inactive) for GTP (active).
What is GAP?
A GTP’ase Activating Protein; this is intrinsic in the alpha-subunit (heterotrimerics; self-limiting) but must be supplied via a separate accessory protein for LMW G-proteins.
What is GDI?
A Guanosine nucleotide Dissociation Inhibitor; currently only associated with LMW G-proteins where they antagonize GEF’s so keeping LMW G-proteins turned off.
What are the 3 subunits of heterotrimeric G-proteins?
Alpha, beta, and gamma
T or F? Ligand/Agonist binds to the G-protein, then the alpha subunit from the GPR affects the effector protein.
False, then the G-protein
T or F? Heterotrimeric G-proteins can either directly interact with effectors or affect the production of secondary messengers.
True
Which class of mechanisms/pathways are involved in mediating the actions of many neurotransmitters, , most peptide hormones, , and Adrenaline, (aka Epinephrine)
Mechanism 2 (Metabotropic)
Extracellular N-terminal plus extracellular “loops” which link the TMDs together forms what on the GPRs?
Recognition sites
Where does Kinase get their phosphate from to phosphoralate?
ATP
Mech 2: Phosphoralation of specialized proteins in the intracellular C-terminal can do what to the GPR?
Turn off or desensitize
How are heterotrimeric G-protein tethered to the inner face of the cell membrane?
By lipid “tails” positioned adjacent to the GPR
Which of the subunits (alpha or Beta-Gamma) affects effectors?
They both can
T or F? G-Protein Alpha-subunit in its inactive form binds to ADP
False, GDP
Which subunit of a heterotrimeric G-protein is the primary effector?
Alpha (but not solely)
Heterotrimeric G-proteins: Alpha subnit has binding sites for ______ nucleotides.
Guanine
After the GPR is activated, there is a translocation through the protein whose intracellular part now becomes a _____ ___ ____
Guanine Exchange Factor (GEF)
T or F? GEF synthesizes GTP from GDP.
False, they exchange
How does the alpha subunit becoming inactive again?
Due to the intrinsic GTPase activity which hydrolyzes the bound GTP back to GDP + phosphate which inactivates the alpha-subunit which then re-associates with the beta-gamma-subunit so inactivating it too.
What increases the rate of hydrolysis by the alpha-subunit?
Regulators of G-protein Signaling (RGS’s)
T or F? All heterotrimeric G-proteins are expressed ubiquitously in all cells and are involved in fundamental/universal cellular functions.
False, only some are not all. Some G-proteins are only found in specialized cells where they are part of that specialized function.
There are hundreds of GPRs involved in odor discrimination but the cells expressing these receptors only contain _____ type of G-protein involved in odor perception.
ONE. (Golf: not found in any other cell type): specificity is given by the GPR and specific “wiring” of the neurons into the brain.
The most well know ubiquitous secondary messengers are the cAMP, how are they synthesized?
By adenylyl cyclases (AC) from ATP when it is stimulated by Alphas(s) subunit. (sub “s” denotes stimulatory”
How are cAMP removed?
By phosphodiesterases,, turns cAMP to AMP
How are cyclic guanine monophosphate (cGMP) generated?
By Guanylyl cyclase.(GC)
How are Diacylglycerol (DAG) and inositol 1,4,5-triphosphate generated?
By phospholipase C (PLC) cleaving PIP2
What are the 5 common secondary messenger?
cAMP, cGMP, Ca2+, DAG, IP3
How are cAMP or cGMP inactivated or removed?
By phosphodiesterases
Phosphodiesterases, can they be regulated?
Yes
T or F? Signaling pathways: the actual “amount” of a secondary messenger is usually determined by the relative activity of both the synthesizing/activating and degrading/inactivating enzymes, producing graded responses rather than either “on” or “off.”
True
T or F?: Mech 3: The metabotropic receptors are GPRs.
False, they are Receptor Tyrosine Kinases (RTKs)
T or F? RTKs when activated becomes phosphoralated and either directly activate other kinases or via adapter/docking proteins, or activate a different type of G-protein, the Low Molecular Weight G-proteins. (LMW G-proteins aka momomeric G-protein)
True
How many domains does RTKs have?
One, but is often not functional until the binding of the messenger extracellularly brings 2 receptors close together “dimerization”
How do RTKs dimerize?
When the primary messenger binds to RTK. Intracellularly this now allows each RTK to cross phosphorylate its partner at specific tyrosine residues.
Auto cross phosphorylation of specific tyrosine residues on the RTKs intracellularly leads to the binding/activation of _______ ______.
Kinase cascades
T or F? RTKs when activated, allows the binding/activation of kinase cascades sometimes involving LMW, G-proteins typified by Ras.
True
Apart from direct activation of kinases, RTKs can often via adapter/docking protein recruit to the membrane ____ ___-____
LMW G-Protein
T or F? LMW G-protein has no intrinsic enzymatic activity.
True
Mech 3: Adaptor protein recruit LMW G-protein to the membrane, this in turns act as a ____, activating an inactive Ras protein which sends an onward transmission of signal.
GEF
The different pathways are very important as they often regulate the fundamental processes like _____ and _______
Growth; differentiation
Kinases ___________ modify specific AA residues in target proteins which alters their activity and/or what they can bind to or interact with.
Covalently
RTKs: The phophoralated tyrosine residues by tyrosine kinases is reversed by _______
Phosphatases
How are phophatases regulated?
Phosphodiesterases
______ of specific tyrosine residues intracellularly on RTKs allows binding of certain proteins that would not bind prior to this process.
Phosphorylation
Family Proteins: Rho
Cytoskeleton
Family Proteins: Rac
Cellular stress
Family Proteins: Ras
Growth
Family Proteins: Rab
Vesicle transport and exocytosis
Family Proteins: Ran
Nuclear trafficking
What is the G-Protein regulatory cycle?
4 different types of accessory proteins that essentially competes to turn on and off GTP (GAPs(on);GIPs(off)) and GDP (GEFs(on);GDIs(off))
LMW G-proteins are also know as _____________
Monomeric G-proteins
Monomeric G-proteins have only one subunit that is like a truncated heterotrimeric alpha subunit: They turn themselves off by means of…….
Accessory proteins
GTPase activity is supplied by _________. Without these the LMW G-protein remains permanently “on”.
GAP
What does constitutively active mean?
Permanently on
T or F? LMW G-proteins can be influenced by 4 different types of of accessory proteins.
True
T or F? Accessory proteins are subject to regulation and “talk” to/intergrate with other proteins involved in other signal translation pathways.
False, transduction pathways
Most of these pathways involve _______ _______ where one activated kinase phosphorylates the next in the sequenece so activating it and so on
Kinase cascades
The end result of kinase cascades often is an effect on _____.
Transcription
T or F? Phosphoralation can only turn on a protein.
False, it can also turn them off
A lipid soluble messengers do not want to go into the blood, they solubilized to an extent by binding to ______ protein.
Plasma
Lipids soluble messengers can go into the cell and cannot be ________ down
Broken
Some chemical messengers can cross the cell membrane and these are recognized by intracellular receptors either in the cytoplasm or nucleus itself: Name them.
Steroid hormones: Aldosterone, cortisol, testosterone, progesterone and the estrogens
Thyroid hormones: thyroxine and triiodothyronine
Mech 4: Upon binding to the their specific receptors both move into the nucleus, (unless already there), and act as ____ ______..
Transcription regulators
T or F? Some recent research however has suggested the presence of cell surface receptors for these hydrophilic molecules: this may be the reason that some produce quite short-latency responses versus affecting transcription which can take hours to days.
False, hydrophobic
T or F? Nitric Oxide (NO) and carbon monoxide (CO) have also been identified as messenger molecules.
True
Which is INCORRECT about nitric oxide?
A. The molecule who’s actions are enhanced by Viagra
B. Stimulates the production of cGMP
C. Is also strongly implicated in immune system function and synaptic transmission in learning and memory
D. Is produced by the enzyme Nitric Oxide Syntase (NOS)
They are all true
CO appear to be involved in _____ function
GI
T or F? NO and CO are stored and are released when needed.
False, they freely cross membranes, they are generated on demand similarly to the steroid hormones
Both NO and CO are rapidly ‘scavenged” (reduce/inactivated) therefore can only act _____
Locally
T or F? Mech 4 messengers are recognize extracellularly.
False, these messengers are membrane soluble and specific receptors are intracellular.
NO and CO diffuse freelly into neighboring cells or even back into the cell that released it, they directly affect target enzymes such as ___ and possible secondary messenger production.
Guanylyl cyclase (GC)
T or F? An agonist binds to a receptor and activates it.
True
T or F? An antagonist binds to a receptor but does not activate it.
True
What accessory/”extra” proteins do you need to turn off a heterotrimeric G-protein?
None, alpha subunits are intrinsic, containing GTPase which will turn themselves off.
What accessory/”extra” proteins do you need to turn off a monomeric/low molecular weight G-protein?
GAP (antagonized by GIP)
T or F? A messenger molecule must be “free” to interact with a receptor:
False, there are contact dependent receptors
An activated GPR (GPCR) has how many TMD’s?
7
An activated RTK (GPCR) has how many TMD’s?
2
The action of kinases is reversed by?
Phosphatases
