Lecture 3 Part 1 Flashcards
recent research has revealed what in detail?
the molecular processes that transduce extracellular signals into intracellular messages that control the function of the cell
true or false
most transmembrane signaling is accomplished by many different types of molecular mechanisms
false – only a few different molecular mechanisms
as mentioned, most transmembrane signaling is accomplished by many different types of molecular mechanisms
what has happened to these mechanisms over the years?
through the evolution of distinctive protein families, they have been adapted to transduce many different signals
name the protein families
-receptors on the cell surface
-intracellular receptors (that aren’t enzymes)
-enzymes
name the known transmembrane signaling mechanisms
-lipid soluble chemical signal that acts on an intracellular receptor
-signal binds to the extracellular domain of transmembrane proteins which activates the enzymatic activity of the cytoplasmic domain
-signal binds to the extracellular domain of a transmembrane receptor bound to a protein tyrosine kinase
-signal binds to and directly regulates the opening of an ion channel
-GPCR
of the 5 known transmembrane signaling mechanisms, which are the most common
protein tyrosine kinase
ion gated channel
GPCR
true or false
the 5 signaling mechanisms stated account for all of the chemical signals conveyed across cell membranes
FALSE it’s around 90%, but they do transduce many of the most important signals pertaining to pharmacotherapy
explain the general format of signaling
an extracellular signaling molecule binds to the receptor. there is then a signal transduction of intracellular signaling proteins.
there are 3 potential targets of these signaling mechanisms:
-metabolic enzyme
-gene regulatory protein
-cytoskeletal protein
when the signal transduction acts on a metabolic enzyme, wha results
altered metabolism
when the signal transduction acts on a gene regulatory protein, what results
altered gene expression
when the signal transduction acts on a cytoskeletal protein, what results
altered cell shape or movement
name the 3 potential target proteins of the signal transduction pathway
metabolic enzymes
gene regulatory protein
cytoskeletal protein
what is another name for a receptor for lipid-soluble agents?
nuclear receptor. The receptor is located in the nucleus of the cell
a lipid-soluble chemical signal can cross the plasma membrane an act on an intracellular receptor.
this receptor may be…..
an enzyme (guanylyl cyclase for NO) or a regulator of gene transcription (nuclear receptor)
give specific examples of substances that are lipid soluble agents that go through the lipid soluble signaling mechanism
nitric oxide (NO)
freely diffusible gas. acts by crossing the membrane and stimulating GUANYLYL CYCLASE – an intracellular enzyme.
NO binds to guanylyl cyclase. GTP loses energy to form cGMP which is a 2nd messenger involved in cell signaling
corticosteroids, mineralocorticoids, sex steroids, vitamin d, and thyroid hormone – work through NUCLEAR RECEPTOR. ligands bind to the intracellular receptor. this allows it to undergo a conformational change that allows them to ENTER THE NUCLEUS to regulate gene expression
name all of the agents which work through the nuclear receptor
corticosteroids
mineralocorticoids
sex steroids
vitamin D
thyroid hormone
explain the mechanism of glucocorticoid hormone mechanism
when the glucocorticoid hormone binds to its normal intracellular receptor, HSP90 falls off. HSP90 is what usually keeps the receptor in the cytoplasm (in the absence of glucocorticoid hormone)
however, when the glucocorticoid hormone binds to the receptor, HSP90 falls off and there is now nothing that is keeping it inside the cytoplasm.
this allows the DNA binding domains and transcription activating domains of the receptor to fold into conformations so that the activated receptor can initiate the transcription of target genes in the nucleus
true or false
HSP90 falls off BEFORE ligand binding
false - after
the mechanism used by HORMONES (act by regulating gene expression - NUCLEAR RECEPTORS) has 2 therapeutically important consequences:—-
-hormones produce their effects after a characteristic LAG PERIOD of 30mins-few hours. this is the time required for the synthesis of new proteins
-the effects of hormones can persist for a few hours or days AFTER the agonist has already been reduced to zero
true or false
the receptor for hormones is the nuclear receptor
true
explain why the effect of hormones can persist for hours or days after the agonist has already been reduced to zero?
because there is a relatively slow turnover of enzymes and proteins – they can remain active in the cell for hours or days after being synthesized.
therefore, the effects of a gene-active hormone will usually decrease very slowly when the administration of the hormone is stopped. lasts long after agonist stops being supplied
name the enzymes involved in adding/removing a phosphate
kinase – adds a phosphate (phosphorylate)
phosphatase - removes a phosphate (dephosphorylate)
ligand-regulated transmembrane enzymes (includes receptor tyrosine kinases) consists of………..
polypeptides consisting of a HORMONE BINDING EXTRACELLULAR DOMAIN and a CYTOPLASMIC ENZYME DOMAIN
class of receptor molecules with an extracellular hormone binding domain and a cytoplasmic enzyme domain.
give 3 examples of these receptors
what are the 2 domains connected by?
protein tyrosine kinase
protein serine kinase
guanylyl cyclase
the 2 domains are connected by a hydrophobic segment of the polypeptide that crosses the lipid bilayer. – called the TRANSMEMBRANE DOMAIN
the class of receptor molecules that includes protein tyrosine kinase (extracellular hormone binding domain and intracellular enzyme domain) mediates the first steps in signaling by…………
insulin
EDGF (epidermal growth factor)
PDGF (platelet derived growth factor)
ANF (atrial natriuretic factor)
TGF-beta - transforming growth factor beta
explain in detail the receptor tyrosine-kinase signaling pathway
-hormone binds to extracellular domain
-change in receptor conformation - the receptors dimerize
-the tyrosine residues in both cytoplasmic domains become PHOSPHORYLATED (each by the other – cross-phosphorylation event called autophosphorylation)
-the receptors catalyze the phosphorylation of tyrosine kinase residues on different downstream signaling proteins (only a few have been identified)
how can tyrosine kinase receptors be useful in drug development for cancer treatment?
if there is no dimerization, there will be no receptor phosphorylation and thus no phosphorylation of downstream substrates. this will lead to NO CELL GROWTH/PROLIFERATION
It is easy to envision therapeutic uses for specific inhibitors of growth factor receptors (protein tyrosine kinase) especially in ______ disorders
neoplastic
what receptor do EGF, PDGF act on
protein tyrosine kinase
the intensity and duration of EGF, PDGF (and other agents that act on tyrosine kinase receptors) are limited by what?
receptor down regulation
when these ligands bind to their receptor, this induces accelerated ENDOCYTOSIS of receptors from the cell surface. Then, the bound ligands and receptors are degraded. (in some instances the receptors are brought back to the surface – receptor-recycling)
nuclear receptor:
cell membrane –> ____ —>____ —____
nuclear membrane
nucleus
gene transcription
endocytosis/degradation >
de novo synthesis of receptors
down regulation
ligand regulated transmembrane enzymes
includes receptor tyrosine kinases
the total number of cell surface receptors (tyrosine kinase type) is down regulated how?
through endocytosis/degradation
leads to a decrease of intensity and duration of EGF, PDGF and other agents that act through this tyrosine kinase type class of receptors
explain receptor mediated endocytosis
ligand binds to the receptor.
clathrin and other adaptor proteins bind to the receptor (inside cell). called EARLY COATED PIT
the components continue to accumulate to eventually break off and form a coated vesicle.
the clathrin and adaptor proteins uncoat and go back to the surface to aid in the next ligands binding.
meanwhile, the receptor + ligand forms a transport vesicle.
in receptor mediated endocytosis, what happens if you don’t allow the receptors/clathrin/other adaptor proteins to get back to the surface before taking another dose?
desensitization. you need a higher dose to get the same effect.
in receptor mediated endocytosis, what forms a “cage” around the forming endosome?
clathrin
what happens in vesicle uncoating
the clathrin coat is removed
what is a CURL endosome? when does it form?
Compartment of Unbinding of Receptor and Ligand
forms after the clathrin coat is removed
in receptor mediated endocytosis, what are the 2 potential fates of the used receptor
it can be recycled back to the surface or be sent to a digestive vacuole and degraded
put the following in order:
-CURL endosome forms
-clathrin vesicle formation
-receptor binding and activation
-coated pit formation
-receptor recycles to the surface or is sent to a digestive vacuole
what class of receptors goes through this?
receptor binding and activation
coated pit formation
clathrin vesicle formation
CURL endosome forms
receptor recycles to the surface or is sent to a digestive vacuole
the receptor that goes through this mechanism are the LIGAND-REGULATED TRANSMEMBRANE ENZYMES (including receptor tyrosine kinase)
explain what happens to receptors after they’re internalized in receptor mediated endocytosis
either receptor degradation – leads to receptor downregulation
or
ligand unbinds and the receptor gets recycled to the membrane
give an example of a receptor that gets degraded and leads to receptor downregulation
EGF receptor (epidermal growth factor) receptor
what does ANP stand for and what does it do
ANP = atrial natriuretic peptide
regulates blood volume and vascular tone. acts on a transmembrane receptor whos intracellular domain as GC (guanylyl cyclase) activity – like receptor tyrosine kinases and receptor serine kinases
true or false
ANP receptors are active in dimeric forms
TRUE
name some receptors for ANP (Atrial natriuretic peptide)
receptor tyrosine kinases
receptor serine kinases
(transmembrane receptors whose intracellular domain has GC - guanylyl cyclase – activity)
true or false
ANP works through tyrosine kinase receptor
true - or serine kinase
explain the mechanism and affects of ANP
ANP binds to tyrosine kinase receptor which causes it to dimerize. autophosphorylation, GTP loses 2 P to become cGMP which is a second messenger and downstream signaling occurs.
this leads to….
-INCREASED SODIUM EXCRETION
-DECREASED ARTERIAL BP (due to vasodilation)
true or false
ANP causes decreased sodium excretion
false - increased
true or false
ANP causes vasoconstriction and this decreased arterial BP
false - vasodilation and thus decreased arterial BP
where is ANP released from
the atria of the heart
will too much or too little sodium cause high BP? explain
too much
sodium causes depolarization and thus contraction of the heart muscle. thus, too much Na will cause high BP
cytokine receptors act through what mechanism?
the JAK-STAT pathway
explain what cytokines are
relatively low MW pharmacologically active proteins that are secreted by the cell to alter either its own function (autocrine) or the effect of adjacent cells (paracrine)
true or false
cytokines are not pharmacologically active
false - they are
true or false
cytokines are relatively low MW
true
cytokine receptors response to what ligands?
a heterogeneous group of peptide ligands. includes:
-growth hormone
-erythripoietin
-interferons
-other regulators of growth and regulation
IL-6
IL-1
IL-13
state whether proinflammatory or antiinflammatory
IL-6 and IL-1 = pro inflammatory
IL-13 = anti inflammatory
true or false
cytokine receptors, like tyrosine kinase receptors, bind to their ligand and then dimerize
true
what does JAK-STAT pathway stand for
JAK = Janus Kinases
STAT = signal transducers and activators of transcription
explain the mechanism of cytokine receptors
ligand binds to cytokine receptor and the receptor dimerizes.
JAK binds noncovalently to the cytoplasmic side of the receptor. the JAK(inases) are now active and phosphorylate tyrosine residues on the receptor. They then recruit STATS (proteins)
a second phosphorylation on tyrosine residues occurs – this time on the STATs.
these phosphorylated STATs then dissociate from the cytoplasmic side of the receptor and form a dimer with EACH OTHER.
this STAT dimer (still phosphorylated) migrates into the nucleus and modulates transcription
true or false
the cytokine receptor mechanism is like an extended form of the tyrosine kinase mechanism
true
many of the useful drugs in clinical medicine act by….
mimicking or blocking the actions of the endogenous ligands that regulate the flow of ions across the plasma membrane
as mentioned, many drugs act by mimicking/blocking the actions of ENDOGENOUS LIGANDS that regulate the flow of ions across the plasma membrane.
give 3 examples of these natural endogenous ligands
acetylcholine
GABA
excitatory amino acids – like glycine, aspartame, and glutamate
what does GABA stand for
gamma-aminobutyric acid
ligand gated ion channels transmit its signal across the plasma membrane by increasing the transmembrane conductance of the ion, thereby,,,,,,
altering the electrical potential across the membrane
what is the normal resting membrane potential in neurons?
what about regular cells?
in neurons = -90mv
in reg cells = -70mv
give an example of a ligand gated channel (receptor)
the Nicotinic Acetylcholine receptor
explain the structure of the Nicotinic acetylcholine receptor
it is pentameric – meaning it contains 5 components:
-2 alpha subunits
-1 beta subunit
-1 gamma subunit
-1 delta subunit
explain the mechanism of the nicotinic acetylcholine receptor when it binds to its ligand
in the ABSENCE of the ligand (acetylcholine), the receptor is closed and does not allow Na+ to rush into the cytoplasm.
when acetylcholine binds (to the alpha subunits) a conformational change occurs and a channel opens to allow the passage of sodium ions.
Na+ now flows INTO THE CELL (depolarization)
____ is one of the best-characterized cell surface receptors
AChR - nicotinic acetycholine receptor
give the approximate MW of each subunit of the nicotinic acetylcholine receptor
each subunit ranges from around 43,000-50,000
true or false
the nicotinic acetylcholine receptor is a ligand-gated ion channel
true
each polypeptide subunit of the nicotinic acetylcholine receptor crosses the lipid bilayer how many times?
4 times
give the approximate time that elapses between the BINDING OF THE AGONIST to a ligand gated ion channel and the CELLULAR RESPONSE.
why is it this time period?
the time between binding and response can be measured in milliseconds.
timing is crucial for the moment-moment transfer across synapses
true or false
the time elapsed between binding and cellular response is measured in MILLISECONDS for all molecular signaling mechanisms
FALSE - only for ligand gated ion channels bc timing is crucial for the moment-moment transfer of information across synapses
other molecular signaling mechanisms may require seconds, minutes, or even hours (ie: hormones that activate gene expression like glucocorticoids)
name 3 second messengers
cAMP (cyclic adenosine-3’,5’-monophosphate)
calcium ion
phosphoinositides
60-70% (most) drugs work through which signaling mechanism?
GPCR
many extracellular ligands act by increasing the INTRACELLULAR concentrations of…..
2nd messengers (like cAMP, calcium ions, and phosphoinositides)
the ligands used in GPCR use a transmembrane signaling system with what componentss?
-an extracellular ligand SPECIFICALLY DETECTED by a cell surface receptor
-the receptor then activates a G protein (on the cytoplasmic side)
-this activated G protein changes the activity of an effector (ie: an enzyme like adenylyl cyclase)
true or false
G proteins contain only 1 or 2 functionally diverse subfamilies
false - several functionally diverse subfamilies
Gs
Gi
Golf
Go
Gq
Gt
name the functionally diverse subfamilies of G proteins
Gs
Gi
Golf
Go
Gq
Gt
what is the G protein that activates adenylyl cyclase?
what activates this G protein?
Gs - activated by a host of hormones and neurotransmitters
-glucagon
-histamine
-catecholamines
-FSH
-adrenocorticotropic hormone
what does Gs stand for
G-stimulatory
true or false
Gs activates adenylyl cyclase as well as calcium channels
true
give 5 examples of endogenous ligands that increase cAMP levels through Gs
-glucagon
-histamine (H2 receptors)
-FSH (follicle stimulating hormone)
-catecholamines (beta adrenoceptors)
-adrenocorticotropic hormone
-
true or false
Gs, when activated, decreases cAMP levels
false - increases
increased cAMP levels causes what?
-increased heart rate and force
-increased vasocontraction
-increased gland secretion
true or false
increased cAMP levels causes decreased glandular secretion
false - increased
true or false
FSH increases intracellular cAMP levels through Gs
true
-along with histamine, glucagon, catecholamines, adrenocorticotropic hormone
