Cell Signalling 1&2 (cell bio) Flashcards
Cell Signalling synonyms are:
?
?
The ability of cells to ? and act on signals from ? their plasma membrane is fundamental to life
Rube Goldberg device (garage door opener, circa 1928) as an analogy for the complex cause-and-effect sequence characteristic of cellular chemical signaling
This whimsical “machine” serves as an analogy for chemical signaling within cells because of the ? control elements, their connection as a cause-and-effect sequence, and the use of household items, similar to the use of evolutionarily conserved proteins of cells in signaling.
(- maybe it will take longer for the aquarium to fill up and trigger the next response so this is characteristic of cell signaling processes
- the types of mechanism for cellular transduction are kind of kept the same throughout evolution within different species)
Cell Signalling synonyms are:
biosignalling
cell communication
- The ability of cells to receive and act on signals from outside their plasma membrane is fundamental to life
- Reception 2. Transduction 3. Response
(all of this involves biochemical process)
(e.g. how the embryo receives signals from the mother’s body and the time to differentiate certain cells and also embryo sends msg to the mother - cellular signaling etc.
- bacteria have their set of receptors to diff signals and understand what going on in the environment so bacteria sense where should i bind, what type of cell to bind to, which pH etc. so all this are part of cell communciation; how ligands will bind to cell receptor and inside cell telling cell what to do)
The receptor can be inside of cell - true false?
so in pic we see a receptor present on PM to which signal binds (1) inside of cell transduction occurs, then we see diff. things happening indicated by blue triangle and circle shape to trigger cellular response which are the red things - pic.
CELLULAR RESPONSE
- altered cell shape or movement (? protein - > are effector proteins)
- altered metabolism -> ? enzyme
(if not enough glucose then cellular transduction telling body what to do or will be telling adipose tissue what to do so will be regulated so cellular signalling cascade pathway happening in between 1st messenger, the signal information and response i.e. transduction.)
Conversion of information into a chemical change:
-> SIGNAL ? (this is the universal property of ALL living cells!!)
true
The receptor can be inside of cell - true false?
so in pic we see a receptor present on PM to which signal binds (1) inside of cell transduction occurs, then we see diff. things happening indicated by blue triangle and circle shape to trigger cellular response which are the red things - pic.
CELLULAR RESPONSE
- altered cell shape or movement (cytoskeleton protein - > are effector proteins)
- altered metabolism -> metabolic enzyme
(if not enough glucose then cellular transduction telling body what to do or will be telling adipose tissue what to do so will be regulated so cellular signalling cascade pathway happening in between 1st messenger, the signal information and response i.e. transduction.)
Conversion of information into a chemical change:
-> SIGNAL TRANSDUCTION (this is the universal property of ALL living cells!!)
SIGNALING PATHWAY
Chain of sequential molecular ? (ligand binding to the receptor, protein kinases switching on and off)
Multiple sites for (all this transduction cascade) ? and for ? drug action (imp. to understand this as this lets us know that if given a certain amount then what it will affect, how much dose to give etc.)
The elements of chemical-signaling pathways are often highly * ? *, the same molecules or same basic types of molecules are used in a wide variety of different stimulus-? pathways
(we have g-protein coupled receptors for e.g. but we have diff. types of G-protein but they kind of act in same away but differently, so it is conserved and gives diff rate of responses depending on transduction pathways)
SIGNALING PATHWAY
Chain of sequential molecular interactions (ligand binding to the receptor, protein kinases switching on and off)
Multiple sites for (all this transduction cascade) regulation and for therapeutic drug action (imp. to understand this as this lets us know that if given a certain amount then what it will affect, how much dose to give etc.)
The elements of chemical-signaling pathways are often highly * conserved *, the same molecules or same basic types of molecules are used in a wide variety of different stimulus-response pathways
Signal - Response
Target cells use different mechanisms to adjust the ways in which they respond to extracellular signals
The speed of a response depends on the turnover of signaling molecules (? change or ? expression - which one is faster?)
* ? feedback loop – output inhibits its own production
* ? feedback loop – output stimulates its own production
Can trigger ? response (gradually increasing concentration of an extracellular signal)
A type of response that may be either complete and of full intensity or totally absent, depending on the strength of the stimulus; there is no partial response. For example, a ? cell is either stimulated to transmit a complete nervous impulse or else it remains in its resting state
Target cells use different mechanisms to adjust the ways in which they respond to extracellular signals
The speed of a response depends on the turnover of signaling molecules (allosteric change or gene expression - which one is faster? -> ALLOSTERIC CHANGE as it just switches on or off and regulate to go a bit slow or faster but for gene expression needs to trigger DNA, synthesize protein etc.
- the diff mechanisms of receptor to ligand will trigger response faster or slower as smtms we have more steps in between ligand binding to receptor and cellular response so maybe 10 steps before cellular response or when ligand bind to receptor response happen straight away so depends on receptor mainly)
- negative feedback loop – output inhibits its own production
- positive feedback loop – output stimulates its own production
Can trigger ALL OR NONE response (gradually increasing concentration of an extracellular signal)
A type of response that may be either complete and of full intensity or totally absent, depending on the strength of the stimulus; there is no partial response. - For example, a nerve cell (AP trigger) is either stimulated to transmit a complete nervous impulse or else it remains in its resting state
SIGNAL TRANSDUCTION - General Properties
a) Specificity:
- signal molecule fits the binding site on its ? receptor; other signals fit or do not fit? (in pic: ligand = 1st messenger molecule (S1) fits into receptor)
b) Amplification:
- when enzymes activate enzymes, the number of affected molecules increases geometrically in an enzyme ?.
c) Desensitization/Adaptation
- Receptor activation triggers a feedback circuit that ? the receptor or removes it from the cell ?.
d) Integration
- when two signals have ? effects on a metabolic characteristic such as the concentration of a second messenger X, or the membrane potential Vm, the regulatory outcome results from the integrated input from both receptors.
SIGNAL TRANSDUCTION - General Properties
a) Specificity:
- signal molecule fits the binding site on its complementary receptor; other signals fit or do not fit? (in pic: ligand = 1st messenger molecule (S1) fits into receptor)
b) Amplification:
- when enzymes activate enzymes, the number of affected molecules increases geometrically in an enzyme cascade.
c) Desensitization/Adaptation
- Receptor activation triggers a feedback circuit that shuts off the receptor or removes it from the cell surface.
(if fear keeps going then cell needs to modulate the release so it desensitizes (ligand or epinephrine being secreted; if keeps secreting adrenaline (Stress) then will run out of energy so need to modulate the release)
d) Integration
- when two signals have opposite effects on a metabolic characteristic such as the concentration of a second messenger X, or the membrane potential Vm, the regulatory outcome results from the integrated input from both receptors.
(Everytime cell receives millions of signals simultaneously so integration is needed to respond accordingly e.g. in neuron cells integrating several inhibitory or excitatory signals until it makes a response)
SIGNAL TRANSDUCTION – General Properties
Signal transductions are highly ? and extremely ?!
(a) Specificity:
* Achieved by precise molecular complementarity between ? and ? molecules,
* In multicellular organisms: specific receptors are present in specific ? types
(adipocyte made with other receptors and will trigger diff. responses, epinephrine in hepatocyte or adipocyte or glucose metabolism, what will epinephrine trigger the hepatocyte to do when glucose is low -> then signal for glycogenolysis being sent to hepatocyte and if sent to adipocyte then that receptor will understand that signal, epin. different as it has diff. enzymes and will perform diff actions)
(b) Sensitivity:
I. ?
Described by dissociation constant Kd
Receptor detects picomolar concentrations
of signal molecule
(if more affinity for ligand then need tiny bits of ligand)
II. Cooperativity
Small changes in ligand concentration cause large changes in receptor activation
III.Amplification by enzyme cascades
Enzyme once activated catalyzes activation of many molecules of a ? enzyme, each of which activates many molecules of third enzyme, and so on
Can produce ? of several orders of magnitude
SIGNAL TRANSDUCTION – General Properties
Signal transductions are highly specific and extremely sensitive!
(a) Specificity:
* Achieved by precise molecular complementarity between receptor and signal molecules,
* In multicellular organisms: specific receptors are present in specific cell types
(adipocyte made with other receptors and will trigger diff. responses, epinephrine in hepatocyte or adipocyte or glucose metabolism, what will epinephrine trigger the hepatocyte to do when glucose is low -> then signal for glycogenolysis being sent to hepatocyte and if sent to adipocyte then that receptor will understand that signal, epin. different as it has diff. enzymes and will perform diff actions)
(b) Sensitivity:
I. Affinity
Described by dissociation constant Kd
Receptor detects picomolar concentrations
of signal molecule
(if more affinity for ligand then need tiny bits of ligand)
II. Cooperativity
Small changes in ligand concentration cause large changes in receptor activation
III.Amplification by enzyme cascades
Enzyme once activated catalyzes activation of many molecules of a second enzyme, each of which activates many molecules of third enzyme, and so on
Can produce amplification of several orders of magnitude
(c) Desensitization (adaptation)
* Cells can ? their sensitivity to a signal
* Continuous presence of a signal can cause desensitization of the ? system, ? the cell response to that level of stimulus
* If stimulus falls below threshold the receptors can be ?
* Enables cells to respond to changes in the concentration of an ? signal molecule over a wide range of signal concentrations
(d) Integration
* Ability of a system to receive ? signals and produce unified and appropriate response
* Each cell type is programmed to respond to specific combinations of extracellular signals
* Each cell type displays a set of ? that enables it to respond to a corresponding set of ? molecules produced by other cells
(c) Desensitization (adaptation)
* Cells can adjust their sensitivity to a signal
* Continuous presence of a signal can cause desensitization of the receptor system, decrease the cell response to that level of stimulus
* If stimulus falls below threshold the receptors can be reactivated
* Enables cells to respond to changes in the concentration of an extracellular signal molecule over a wide range of signal concentrations
(d) Integration
* Ability of a system to receive multiple signals and produce unified and appropriate response
* Each cell type is programmed to respond to specific combinations of extracellular signals
* Each cell type displays a set of receptors that enables it to respond to a corresponding set of signal molecules produced by other cells
SOME SIGNALS TO WHICH CELLS RESPOND
- ?
- Cell surface ?/oligosaccharides
- Developmental signals
- ? matrix components
- Growth factors (growth factor -> response over some imte (stem cell into mature cell; olfactory into mature cell here; mechanical touch can also trigger immune response; )
- ?
- Hydrophilic
- Lipophilic
(basically ALL SIGNALS)
SOME SIGNALS TO WHICH CELLS RESPOND
- antigens (present on pathogens)
- Cell surface glycoproteins/oligosaccharides
- Developmental signals
- extracellular matrix components
- Growth factors (growth factor -> response over some time (stem cell into mature cell; olfactory into mature cell here; mechanical touch can also trigger immune response; )
- Hormones
- Hydrophilic
- Lipophilic
(basically ALL SIGNALS)
- glycoprotein cell receptors: surface carbohydrates on cells serve as points of attachment for other cells, infectious bacteria, viruses, toxins, and many other molecules.
SOME SIGNALS TO WHICH CELLS RESPOND
- Mechanical touch (mechanotransduction)
- ? (phototransduction)
- ?
- Neurotransmitters
- Nutrients
- ?
- Tastants
- ?
SOME SIGNALS TO WHICH CELLS RESPOND
- Mechanical touch (mechanotransduction)
- light (phototransduction)
- osmolarity
- Neurotransmitters
- Nutrients
- odorants
- Tastants
- pheromones
(diff.taste: diff transduction; Na = // bitter sweet taste working through G protein coupled receptor; acid)
CELL SIGNALING MECHANISMS
** Despite the many different types of biological signals, there is a remarkable degree of ? of signaling mechanisms during evolution! **
1000s of different types of biological signals and different responses caused by these signals
** the machinery for transducing these signals is built from about #? basic types of protein components **
We will study some examples of the major classes of signaling mechanisms and how they are integrated in specific biological functions
(transmission of nerve signals, responses to hormones and growth factors, etc.)
CELL SIGNALING MECHANISMS
** Despite the many different types of biological signals, there is a remarkable degree of CONSERVATION of signaling mechanisms during evolution! **
1000s of different types of biological signals and different responses caused by these signals
** the machinery for transducing these signals is built from about 10 basic types of protein components **
LIGANDS (can be called # messengers too!)
From the Latin word ligare, meaning “to ?”
* Are ? metabolized to useful products
* Are not ? in any cellular activity
* Have no ? properties
*Their only function is to change the properties of the ? *
The binding of a ligand with receptor results in a cellular effect
→ changes in that cell (altering gene transcription or translation, changing cell morphology, stimulating secretion of a molecule…)
LIGANDS (can be called # messengers too!)
From the Latin word ligare, meaning “to bind”
* Are NOT metabolized to useful products
* Are not intermediates in any cellular activity
* Have no enzymatic properties
Their only function is to change the properties of the RECEPTOR (not enzyme as its binding to receptor)
The binding of a ligand with receptor results in a cellular effect
→ changes in that cell (altering gene transcription or translation, changing cell morphology, stimulating secretion of a molecule…)
LIGANDS (FIRST MESSENGERS)
Canoriginatefromdifferenttypesofmolecules:
* Proteins
* Small peptides
* Amino acids
* Nucleotides
* Steroids (steroid hormone derived from cholestrol)
* Retinoids
* Fattyacidderivatives
* Gases(NitricOxideandCarbonmonoxide)
- EX: Hormones, ? factors, extracellular matrix components and ?
growth factors, and neurotransmitters
AGONISTS AND ANTAGONISTS
Agonist: structural ? to specific ligands that bind to a receptor and ? the effects of its natural ligand
Antagonist: ? that bind to the receptor ? triggering the normal effect and thus ? the effects of agonists, including the biological ligand
Sometimes the affinity of the synthetic agonist or antagonist for the receptor is greater than that of the natural agonist/antagonist e.g agonist drug: binds to a receptor and produces enhanced cellular activity (before drug: normal cell activity); the antagonistic drug blocks cellular activity
AGONISTS AND ANTAGONISTS
Agonist: structural analogs to specific ligands that bind to a receptor and mimics the effects of its natural ligand
Antagonist: analogs that bind to the receptor WITHOUT triggering the normal effect and thus blocks the effects of agonists, including the biological ligand
LIGANDS (FIRST MESSENGERS)
Neurotransmitters
- ? chemicals that enable neurotransmission
They transmit signals across a synapse:
* From one neuron to another ?
* From neuron to ? cells
* From neuron to ? cells
parasympathetic: ? is the main neurotransmitter in neuromuscular junction
SOMATIC/SKELETAL: ? acetylcholine receptor
SMOOTH, CARDIAC: nicotonic or muscarinic? acetylcholine receptor
LIGANDS (FIRST MESSENGERS)
Neurotransmitters (are ligands - first messengers)
- endogenous chemicals that enable neurotransmission
They transmit signals across a synapse:
* From one neuron to another target neuron cell
* From neuron to muscle cells
* From neuron to gland cells
parasympathetic: acetylcholine is the main neurotransmitter in neuromuscular junction
SOMATIC/SKELETAL: nicotinic acetylcholine receptor
SMOOTH, CARDIAC: muscarinic acetylcholine receptor (muskan = more ppl wanna be happy so smooth and cardiac)
soma”ti”c = nico”ti”nic
FYI - just a reminder!
NEUROTRANSMITTERS
- Amino acids: GABA (γ-aminobutyric acid), glutamate
- Amines: acetylcholine, serotonin
- Catecholamines: dopamine, norepinephrine,
epinephrine - Peptides: endorphins and endogenous opioids (leu-encephalin, met-encephalin, β-endorphin)
- Atypical (nontraditional):
Gases (NO, CO); Endocannabinoids
CELL SIGNALING – Can be mechanical or biochemical
Biochemical signaling:
1. Intracrine: signals are produced by target cell and stay ? this cell
(i.e., ? cells growth factor)
2. Autocrine: signals are produced by the target cell, are secreted, and affect the ? cell itself via receptors
(i.e., immune cells ? ?)
3. Paracrine: signals target cells ? the emitting cell (i.e., ? - v close to post-synaptic membrane, skin cell’s local ? reaction)
4. Endocrine: signals target ? cell, via ? that are released into the bloodstream
(i.e.,cortisol, insulin, glucagon, progesterone)
PIC MAKES IT MORE CLEAR IN ANS!
CELL SIGNALING – Can be mechanical or biochemical
Biochemical signaling:
1. Intracrine: signals are produced by target cell and stay within this cell
(i.e., immune cells growth factor)
2. Autocrine: signals are produced by the target cell, are secreted, and affect the target cell itself via receptors
(i.e., immune cells T lymphocytes)
3. Paracrine: signals target cells nearby the emitting cell (i.e., neurotransmitters - v close to pre-synaptic membrane, skin cell’s local allergic reaction)
4. Endocrine: signals target distant cell, via hormones that are released into the bloodstream
(i.e.,cortisol, insulin, glucagon, progesterone)
RECEPTORS and EFFECTOR PROTEINS
A receptor is a ? molecule that receives chemical ? from ? or ? of the cell
The binding of a ligand (signal) activates the receptor which in turn activates ? signaling pathways/systems
Intracellular signal proteins process the signal and distribute it to specific ? targets (effector proteins)
? proteins elicit cellular responses to signaling molecules (recall that pic in the beginning of lecture)
if the cellular response to a particular signaling molecule is shape change, the effector proteins would be enzymes that remodel the ?
RECEPTORS and EFFECTOR PROTEINS
A receptor is a protein molecule that receives chemical signal from inside or outside of the cell
The binding of a ligand (signal) activates the receptor which in turn activates intracellular signaling pathways/systems
Intracellular signal proteins process the signal and distribute it to specific intracellular targets (effector proteins)
EFFECTOR proteins elicit cellular responses to signaling molecules (recall that pic in the beginning of lecture)
if the cellular response to a particular signaling molecule is shape change, the effector proteins would be enzymes that remodel the cytoskeleton
(Secondary messengers are capable of crossing the phospholipid bilayer cell membrane, whereas primary messengers often are not.
Examples of first messengers are steroid hormones, growth factors, chemoattractants and neurotransmitters.
Examples of second messengers are cyclic adenosine monophosphate (cAMP), calcium ions, nitric oxide, cyclic guanosine monophosphate (cGMP) and phospholipids.)
CELL SURFACE RECEPTORS
1. Metabotropic receptor:
* Membrane receptor of eukaryotic cells that acts
through a * ? messenger *
examples: ? coupled receptors, receptor tyrosine ?
some signal transduction happening in pic
CELL SURFACE RECEPTORS
1. Metabotropic receptor:
* Membrane receptor of eukaryotic cells that acts
through a * first messenger *
examples: G-coupled receptors, receptor tyrosine kinase
some signal transduction happening in pic
- Ionotropic receptor:
- Ligand-gated ion channels
*Forms ion channel ? →ligand binding activation → ? the channel
- Excitatory or inhibitory effects depend on the ? potential of the ion they pass
i.e., Excitatory ionotropic receptors increase ? permeability across the membrane, whereas inhibitory ionotropic receptors increase ? permeability.
Example: ? (smooth and cardiac) ? receptors
- Ionotropic receptor:
- Ligand-gated ion channels
*Forms ion channel pores → ligand binding activation → opens the channel - Excitatory or inhibitory effects depend on the equilibrium potential of the ion they pass
i.e., Excitatory ionotropic receptors increase sodium permeability across the membrane, whereas inhibitory ionotropic receptors increase chloride permeability.
(so after ions pass through channel then can have either inhibitory or excitatory response
- if sodium going in then excitatory cuz raising the voltage thus bringing it closer to the threshold
-> - 70 resting membrane potential as sodium ions go through channels to the inside so now MORE POSITVE on inside of cell as Na is Na+ thus pushing it towards the threshold number i.e. - 55
- however if chloride ions i.e. Cl- then pushing it away from threshold number as more - inside so associated with inhibitory signal)
Example: nicotinic acetylcholine receptors
SECOND MESSENGERS
? molecules generated in large or small? amounts in response to ? activation
Diffuse close to or away? from their source and spread the signal to other parts of the cell by
Binding to and ? the behavior of selected signaling or ? proteins
There are only a few second-messenger systems within ? cells
TYPES OF 2nd MESSENGERS:
1. Hydrophobic
- ?
- ?
- Hydrophilic
- ?
- ?
- IP3
- ? - Gases (gases can go through PM)
- NO
- H2S
- CO
SECOND MESSENGERS
signalling molecules generated in large amounts in response to receptor activation
Diffuse away from their source and spread the signal to other parts of the cell by
Binding to and alter the behavior of selected signaling or effector proteins
There are only a few second-messenger systems within animal cells
(Diacylglycerol (glycerol w 2 FAs): molecule for energy storage in adipocytes -> lipophilic/hydrophobic & diacylglycerol is part of PM phospholipid)
TYPES OF 2nd MESSENGERS:
1. Hydrophobic
- diacylglycerol
- phospholinositols
- Hydrophilic
- cAMP
- cGMP
- IP3 (inositol 1, 4, 5 triphosphate)
- Ca2+ - Gases (gases can go through PM)
- NO
- H2S
- CO
in pic (the blue ones): second messengers will be acting here (blue) in this middle pathway, right in this signal transduction chain to produce similar response!
MOLECULAR SWITCHES
(this ability to switch on and off is v imp. in the signal transduction pathway!)
- Proteins act as ? signaling molecules by activating another protein in a ? pathway
- To do this, proteins can switch between ? and ? states, thus acting as molecular switches in
response to another ? - The ? signal flipping the molecular switch could be
a protein ?, which adds a phosphate group to the ?
a protein ?, which removes phosphate groups
When receiving a signal, they switch from an inactive to an ? state → Until ? process switches them off
Very important in the ? signaling pathway
MOLECULAR SWITCHES
(this ability to switch on and off is v imp. in the signal transduction pathway!)
- Proteins act as intracellular signaling molecules by activating another protein in a signalling pathway
- To do this, proteins can switch between active and inactive states, thus acting as molecular switches in response to another signal
- The external signal flipping the molecular switch could be
a PROTEIN KINASE, which adds a phosphate group to the protein
a PROTEIN PHOSPHATASE, which removes phosphate groups
When receiving a signal, they switch from an inactive to an active state → Until another process switches them off
Very important in the intracellular signaling pathway
- we’ll see that alpha subunit of G protein will have intrinsic switch off, it will diff. than the switches mentioned above so for this inactive protein in pic, the molecular switch will be this protein that can be activated or inactivated through a protein kinase or a phosphatase, which will be adding or removing phosphate groups to this protein and turning them on or off.
G-PROTEINS -> IMPORTANCE
GPCRs (Gproteincoupledreceptors) are involved in many common ?, including allergies, depression, ?, diabetes, ? diseases
Nearly half of all drugs currently available work by targeting different ?
- All G proteins share a common feature: they can become activated and then, after a short time, can ? themselves:
they serve as molecular ? switches with built-in ? *
Example: β-adrenergic receptor, which mediates effects of epinephrine:
Prototype for all GPCRs, used as a model for signal ?
target of * ‘ ? ’ *
Similar receptors: ?, angiotensin II and glucagon
Nobel Prize in Physiology and Medicine in 1994 for their discovery of G-proteins and their role in signal transduction in cells - Alfred G. ? & Martin ?
GPCRs (Gproteincoupledreceptors) are involved in many common diseases, including allergies, depression, blindess, diabetes, cardiovascular diseases
Nearly half of all drugs currently available work by targeting different GPCRs
- All G proteins share a common feature: they can become activated and then, after a short time, can inactivate themselves:
they serve as molecular binary switches with built-in timer *
Example: β-adrenergic receptor, which mediates effects of epinephrine:
Prototype for all GPCRs, used as a model for signal transduction
target of * ‘ beta-blockers ’ *
Similar receptors: serotonin, angiotensin II and glucagon
Nobel Prize in Physiology and Medicine in 1994 for their discovery of G-proteins and their role in signal transduction in cells - Alfred G. Gilman & Martin Rodbell; they used beta-adrenergic receptor (still used today to study receptors and how they transduce information).
G-PROTEIN COUPLED RECEPTORS (GPCR) - OVERVIEW
- Metabotropic receptors (? membrane proteins composed of a single ? ? chain)
- Bind to a particular type of G protein (Gs Gi Gq)
? signal pathway (Stimulatory - Gs and Inhibitory –Gi)
? (PIP2), ?/? pathway (Gq protein)
Mediate most responses to signals from the ? world, as well as signals from other cells
* Hormones, ? and local mediators
* About 900 types have been identified in humans: >350 for detecting ? and other endogenous ligands, >500 ? and ? receptors
red long line in pic is integral polypeptide chain on which an active site for ligand to bind, will be present on the extracellular area as they are cell surface receptors and on chain there will also be an intracellular site for G-protein to bind to
NOTE: the red chain is the Gprotein-coupled receptor as it’s coupled to G-protein; numerous types of G-protein only talking Gs, Gi and Gq (polypeptide Q which is mostly stimulatory)
G-PROTEIN COUPLED RECEPTORS (GPCR) - OVERVIEW
- Metabotropic receptors (integral membrane proteins composed of a single transmembrane polypeptide chain)
- Bind to a particular type of G protein (Gs Gi Gq)
cAMP signal pathway (Stimulatory - Gs and Inhibitory –Gi)
Phosphatidylinositol (PIP2), DAG/IP3 pathway (Gq protein)
Mediate most responses to signals from the external world, as well as signals from other cells
* Hormones, neurotransmitters and local mediators
* About 900 types have been identified in humans: >350 for detecting neurotransmitters and other endogenous ligands, >500 olfactory and gustatory receptors
GPCR MECHANISM - COMPONENTS
- A plasma membrane ? (GPCR) with #? transmembrane helical segments
- G- protein (Gs Gi Gq)
- An ? enzyme in the plasma membrane generating an intracellular or extracellular? second messenger
- A ? ? binding protein (GDP/GTP) which activates the G-protein ?-subunit
Once stimulated by receptor activation → the G protein exchanges bound GDP for ?
GPCR MECHANISM - COMPONENTS
- A plasma membrane receptor (GPCR) with 7 transmembrane helical segments
- G- protein (Gs Gi Gq)
- An effector enzyme in the plasma membrane generating an intracellular second messenger
- A guanosine nucleotide binding protein (GDP/GTP) which activates the G-protein alpha-subunit
Once stimulated by receptor activation → the G protein exchanges bound GDP for GTP
(the effector protein seen in pic will be diff. for cyclicAMP and PIP pathway
Pic explanation:
- so ligand binds to receptor (red chain) which causes a change in the shape of the receptor, the G protein (circled in pic) will change shape as well and changes the GDP that was linked there by a GTP molecule
- So once GTP binds here, the alpha subunit will separate from the beta and gamma subunits (right most ones), and then will come on the effector enzyme (“AC” adenylate cyclase in pic) to activate it.
- And so this enzyme here will convert ATP that is available in the cytosol with this cell to cyclic AMP (LOTS of cAMP produced)
- And then cyclic AMP (cAMP -> second messenger) will activate other cellular function
G-proteins
Membrane-associated * ? * proteins that transmit the signal into the cell ?
o Consist of #? different subunits (α, β, and γ)
o Bind directly to the ? domain of GPCRs
G-proteins
Membrane-associated * heterotrimeric * proteins that transmit the signal into the cell interior
o Consist of 3 different subunits (α, β, and γ)
o Bind directly to the cytoplasmic domain of GPCRs
Pic:
1. initially the G-protein is bound to low energy GDP
2. once the ligand binds to the transmembrane protein receptor, a conformational change occurs in the entire system
3. resulting in -> alpha subunit of G-protein separating itself from the beta, gamma subunits, receptor and the GDP molecule as well in exchange for GTP molecule full of energy
continuing from other flashcard about producing cAMP from alpha-subunit and all
- cyclic AMP is then going to activate the protein ? and let’s see how this happens.
- when I have lots of cyclic amp in the cytosol, they will bind to their regulatory or active? site of the PKA (protein kinase A) i.e. kinase of the system.
- PKA is an ? enzyme that has an active AND a regulatory site
- So the cyclic AMP is binding to the regulatory site, ? this protein kinase.
- the active site part of the protein kinase A, (which is associated with the entire pathway in pic) is then going to ? or ? other proteins in the cytosol triggering a cellular ?.
(THUS, many steps on this signal transduction pathway start from the ? binding to receptor, changing shape, (causing a conformational change in G protein), how G protein will bind to GTP and GDP,
binding to GTP will lead to alpha subunit get ? separating itself from beta gamma subunits and and activates the adenylyl cyclase, the ? enzyme on the membrane.
So this enzyme will turn ATP into ?, increasing the concentration of cyclic AMP in the cytoplasm.
So cyclic AMP is binding to the ? site of the PKA, its protein kinase A and it gets activated and in turn turns on or off other ? in the cytoplasm.)
continuing from other flashcard about producing cAMP from alpha-subunit and all
- cyclic MP is then going to activate the protein kinase and let’s see how this happens.
- when I have lots of cyclic amp in the cytosol, they will bind to their regulatory site of the PKA (protein kinase A) i.e. kinase of the system.
- PKA is an allosteric enzyme that has an active AND a regulatory site
- So the cyclic AMP is binding to the regulatory site, activating this protein kinase.
- the active site part of the protein kinase A, (which is associated with the entire pathway in pic) is then going to turn on or off other proteins in the cytosol triggering a cellular response.
(THUS, many steps on this signal transduction pathway start from the ligand binding to receptor, changing shape, (causing a conformational change in G protein), how G protein will bind to GTP and GDP,
binding to GTP will lead to alpha subunit get activated separating itself from beta gamma subunits and and activates the adenylyl cyclase, plays effector enzyme on the membrane.
So this enzyme will turn ATP into cyclic AMP, increasing the concentration in the cytoplasm of cyclic AMP.
So cyclic MP is binding to the regulatory site of the PKA, its protein kinase A and it gets activated and in turn activate other proteins in the cytoplasm.)
(And here our example is the beta adrenergic receptor binding to epinephrine and then getting to this activation of the PKK)
below info pic in ANS.
Epinephrine binds to ? receptors and exerts its downstream effect through the activation of ? ? (AC) and increase in [ ? ]
* cAMP allosterically activates ?
-> PKA has ? (active site) and regulatory subunits
PKA catalyzes the phosphorylation of other proteins:
* ? ? kinase → mobilization of ? stores in liver and muscle in preparation for the need of energy
Different proteins can be controlled by PKA → they all share an ? sequence that marks them for regulation by PKA (regulatory site)
(so different proteins can be controlled by PKA they all share an amino acid sequence that marks them for regulation by PKA, thus it will have a regulatory site for PKA)
(And here our example is the beta adrenergic receptor binding to epinephrine and then getting to this activation of the PKK)
below info pic in ANS.
Epinephrine binds to adrenergic receptors and exerts its downstream effect through the activation of Adenylyl cyclase (AC) and increase in [cAMP]
* cAMP allosterically activates PKA
-> PKA has catalytic (active site) and regulatory subunits
PKA catalyzes the phosphorylation of other proteins:
* glycogen phosphorylase kinase → mobilization of glycogen stores in liver and muscle in preparation for the need of energy
Different proteins can be controlled by PKA → they all share an AA sequence that marks them for regulation by PKA (regulatory site)
(so different proteins can be controlled by PKA they all share an amino acid sequence that marks them for regulation by PKA, thus it will have a regulatory site for PKA)
EPINEPHRINE CASCADE
Signal transduction entails several steps that ? the original hormone signal
Binding of hormone (protein) activates receptor → ?
Each active ? stimulates the synthesis of many ?
Each PKA phosphorylates many target ?
Net effect of cascade: the ? of the hormone signal by several orders of magnitude
Signal transduction entails several steps that AMPLIFY the original hormone signal
Binding of hormone (protein) activates (beta-adrenergic) receptor → Gs
Each active Gsa (alpha subunit) stimulates the synthesis of many cAMP
Each PKA phosphorylates many target enzymes
Net effect of cascade: the AMPLIFICATION of the hormone signal by several orders of magnitude
the green one will be that is stimulatory one and we see some examples the epinephrine receptor, the beta adrenergic receptor for example, or a glucagon effect, a receptor or a h m receptor.
Okay. So here the ligand will bind here and then we will activate the g alpha subunit that will exchange GTP or GDP
will get activated (pointing at 2nd blue one) and will stimulate adenylate cyclase to produce cyclic AMP on this stimulatory pathway.
Okay. So if we talk about an inhibitory receptor complex with its g inhibitory protein.
in some e.g. we have here somatostatin or adenosin
The ligand is binding to the yellow (last one), right? So you still have the activation of the alpha subunit, which will exchange GDP for GTP gets active and it goes in binds to adenylate cyclase , but instead is stimulating production of cyclic AMP.
It will block it. Okay, so it will inhibit the formation of cyclic AMP and consequently we don’t have PKA activated and then we don’t have cellular response.
G-protein couple receptors: e.g. prostaglandins: arachadonic acid; beta-adrenergic
This is just a reminder on these two different things, the intrinsic activity of the alpha subunit consisting of GTP in the center (one the left of GAP in pic) and GAP so there are 2 diff. things helping to terminate the signal.
DESENSITIZATION
In continued presence of epinephrine:
* Β-adrenergic receptor ? (βARK) is drawn to receptor and ? it, creating a binding site for ? (β-arr)
* Binding of (β-arr) stops interaction between receptor (pink thing in pic) and ?
- It also initiates receptor ?: removal of receptors from membrane into intracellular vesicles by endocytosis (pink thing - receptor, attached to middle circle as see in pic)
- Receptors in endocytic vesicles ?, β-arr dissociates, then receptors can return to membrane (this happens as soon as epinephrine’s conc. are low) and re-sensitize the system to epinephrine
(Right. So it can immediately respond to epinephrine again if is required)
In continued presence of epinephrine:
- Β-adrenergic receptor kinase (βARK) is drawn to receptor and phosphorylates it, creating a binding site for β-arrestin (β-arr)
- Binding of (β-arr) stops interaction between receptor and G protein
- It also initiates receptor sequestration: removal of receptors from membrane into intracellular vesicles by endocytosis
- Receptors in endocytic vesicles dephosphorylates, β-arr dissociates, then receptors can return to membrane and re- sensitize the system to epinephrine
SIGNAL TERMINATION
Desensitization reduces the cellular response even while the signal continues
5 ways by which target cells can become desensitized to a signal molecule (1st 2 most IMP!!!- know diff btw 1st 2 of em)
1st one in pic:
Okay. So sequestration, we just take from the membrane chip for a while and then we can put it back when it’s required.
2nd one in pic: So and this just differentiates from this other type of regulation or termination of signal called receptor DOWNREGULATION.
And so the downregulation, once these receptors are in these vesicles inside of the cell, then the cell decides that actually needs to break down this receptor.
So we have lysosomes with digestive enzymes coming in, binding to this vesicle full of receptors, and it will digest as receptors so no more receptors.
And if the cell needs to be re-sensitized to that ligand, for example, then it will need to produce this receptor again.
- DOWNREGULATION takes LONGER than sequestration as resensitizing those receptors AGAIN!
So it’s a different type of response depending on the ligand, the cell, and what is happening in the body.
(Okay. We will see that this sort of termination signal, termination, it’s v much a use for the receptor tyrosine kinase binding to insulin)
3rd one in pic:
Receptor inactivation: a specific type of protein can come in, bind to the receptor and it will inactivate receptor.
4th one in pic:
inactivation of the signaling protein e.g. G protein by a for instance, a drug
5th one:
And also we can have the Production of inhibitory proteins (orange) that will enter this cycle here
We have the beta adrenergic receptors here in the lungs, in the bronchioles and in the cardiac muscle
LUNGS
- in lungs, this smooth muscle mostly about beta two receptors however in cardiac muscle is mostly beta 1
if adrenergic receptors, then binding to which ligand? -> Catecholamines, Right. Epinephrine, for example, we’re talking about here.
- after ligand binds to receptor, the response of the smooth muscle in lungs and cardiac muscle is diff.
during adrenergic response, smooth muscle in the LUNGS is muscle relaxation because we want to increase the diameter of these bronchioles to allow air passage to be easier for more oxygen going thru the exchange of gases.
CARDIAC MUSCLE: The adrenaline or epinephrine is increasing contraction in cardiac muscle. thus very different responses.
So that’s the beauty of understanding these mechanisms and understanding how I can address certain types of problems with a specific drug. (So if I give a beta blocker, which is not specific for beta receptors, then the pulmonary system the bronchioles in lungs will be contracted instead of relaxed THUS BREATHING WILL BE DIFFICULT
TARGET BETA 2 RECEPTORS (found in lungs) to not increase heart rate or contractility of the heart.
takeaway: the same ligand and produce very different cellular responses depending where it is.
