Cell Signalling Flashcards
1
Q
Signaling molecules are released from secretory cells into the blood and carried to distant target tissues
A
Endocrine signaling
2
Q
Signaling molecules exert their effects locally on neighboring cells: they reach these target cells via the interstitial fluid
A
Paracrine signaling
3
Q
Signaling molecules bind to receptors in or on the cells that release them
A
Autocrine signaling
4
Q
Concentration of ligan at which 1/2 of the receptors are occupied
A
Kd
5
Q
Kd = ?
A
[L][R] / [LR}
6
Q
The slope of a receptor-ligand binding graph is?
A
-Ka
7
Q
Adrenergic receptor type in vascular smooth muscle
A
alpha-1
8
Q
Adrenergic receptor type in pancreatic beta cells
A
alpha-2
9
Q
Adrenergic receptor type in liver, bronchial smooth muscle, and adipose tissue
A
beta-2
10
Q
Adrenergic receptor type in the heart
A
beta-1
11
Q
What do adrenergic receptors bind?
A
catecholamines
12
Q
ACh receptors in the parasympathetic nervous system have a high specific affinity for…
A
muscarine (muscarinic receptors)
13
Q
ACh receptors in the skeletal muscle have a high specific affinity for…
A
nicotine (nicotinic receptors)
14
Q
Structural analog of a naturally occurring signaling molecule that binds the receptor for that signaling molecule and mimics the responses induced by the naturally occurring molecule
A
agonist
15
Q
structural analogs that bind a receptor for a signaling molecule but do not elicit a response. Since they interfere with the binding of the naturally occurring signaling molecule to the receptor, they block the action of that signaling molecule.
A
antagonist
16
Q
What type of channel is a nicotinic acetylcholine receptor?
A
Ligand-gated cation channel
17
Q
Largest family of enzyme-linked receptors that have activity in the cytoplasmic domain of the receptor
A
receptor tyrosine kinase family
18
Q
Largest family of cell surface receptors in the human genome
A
G protein-coupled receptors (GPCRs)
19
Q
The extracellular N domain of G protein coupled receptors has how many loops?
A
3
20
Q
What are the three subunits of G proteins?
A
alpha, beta, gamma
21
Q
Subunit(s) of G proteins which are tethered to the plasma membrane by covalent bond with membrane lipids
A
alpha and gamma
22
Q
Which G protein subunits stay coupled during signaling?
A
beta and gamma
23
Q
G proteins are ____ when GTP occupies the guanine nucleotide binding site
A
active
24
Q
G proteins are ____ when GDP occupies the guanine nucleotide binding site
A
inactive
25
In GPCRs, what has GTPase activity
alpha subunit
26
Plasma membrane associated enzyme that catalyzes the conversion of ATP to cycle AMP (cAMP)
Adenylyl cyclase
27
Stimulatory G protein (stimulates adenylyl cyclase activity)
Gs
28
Inhibitory G protein (inhibits adenylyl cyclase activity)
Gi
29
What happens when an extracellular signaling molecule binds to a GPCR
It acts like a guanine nucleotide exchange factor, facilitating the release of GDP and binding of GTP to the alpha subunit
30
What happens when Gαs binds to its target?
Adenylyl cyclase is activated, catalyzing the conversion of ATP to cAMP.
31
What does the beta-gamma complex activate in some instances?
ion channels
32
What does cAMP activate in the GPCR cascade?
Protein Kinase A
33
How is Protein Kinase A activated?
cAMP binding to the regulatory subunit causes the regulatory and catalytic subunits to dissociate
34
What does phosphodiesterase convert cAMP to?
5' AMP
35
Which residues does PKA phosphorylate?
Ser and Thr
36
What does the catalytic subunit of PKA phosphorylate to activate in the nucleus?
CREB
37
The phosphorylated CREB dimer binds to what in the regulatory region of cAMP-inducible genes
cAMP Response Element (CRE)
38
The coactivator protein that links phosphorylated CREB with the basal transcription machinery
CBP/300
39
Preferential targeting of PKA-mediated phosphorylation to specific subcellular location can be achieved by means of _____
A-Kinase Anchoring Proteins (AKAP)
40
A-Kinase Anchoring Proteins (AKAP) are what kind of proteins?
Scaffolding proteins. This allows PKA to be integrated with other signaling events.
41
cAMP induces most of its actions by activating PKA. What else does it have a direct effect on?
ion channels
42
What enters intestinal epithelial cells and induces a process that modifies Gsα, blocking GTPase activity. Gs stays active.
Cholera Toxin
43
Herbal extract from the plant Coleus forskohlii which has a direct stimulatory effect on adenylyl cyclase
forskolin
44
Caffeine inhibits...
phosphodiesterase activity
45
Beta-adrenergic receptor agonist
isoproterenol
46
Beta-adrenergic receptor antagonist
propranolol
47
In M2 muscarinic receptors in the heart, beta-gamma subunits released by Gi do what?
Bind to and open K+. Efflux of K+ hyperpolarizes the plasma membrane.
48
Toxin that covalently modifies Gαi so that it stays in the GDP form (inactive)
pertussis toxin
49
Five ways to terminate the GPCR/cAMP signaling pathway?
1) dissociation and degradation of signaling molecules
2) intrinsic GTPase activity
3) phosphodiesterase
4) phosphatase action on PKA-phosphorylated proteins
5) GPCR down-regulation
50
GTPase activity of the G alpha subunit can be enhanced by what?
Regulatory of G protein signaling proteins (RGS)
51
A state of reduced responsiveness of a tissue to an agonist that develops in response to the continuous or repeated stimulation of the tissue by that agonist
Densensitization
52
Two things that can desensitize Gs protein-coupled receptors
1) receptor phosphorylation by PKA
| 2) beta-arrestin binding to the receptor
53
In beta-adrenergic receptors, how does feedback inhibition by PKA work?
PKA phosphorylates Ser/Thr residues nearby the cytosolic domain of Gs which usually interact with and activate Gs, diminishing the response of the target tissue to further stimulation by epinephrine.
54
Kinases that phosphorylate specific serine and threonine residues on the cytosolic domain of G protein-coupled receptors only when the receptor is in an active conformation induced by the occupation of the ligand-binding site by a compatible hormone or agonist.
G protein-coupled receptor kinases (GRKs)
55
The serine and threonine residues phosphorylated by beta-ARK serve as binding sites for ____
beta-arrestin
56
Recruited to the plasma membrane where it phosphorylates specific serine and threonine residues on the beta-adrenergic receptor.
Beta-Adrenergic Receptor Kinases (beta-ARK)
57
Binding of beta-arrestin to the phosphorylated receptor blocks what?
It blocks the coupling of G proteins with the receptor
58
Do PKA and beta-ARK target the same or different serine/threonine residues?
different
59
What recruits beta-ARK to the membrane?
Gsβγ
60
Which two proteins does beta-arrestin work with to promote endocytosis of receptors?
Clathrin and AP2 (components of clathrin-coated pits)
61
Why does receptor endocytosis result in a net decrease in the receptor content of the plasma membrane?
Some are degraded
62
What happens to endocytosed receptors which will be recycled?
Dephosphorylated and translocated back to the plasma membrane
63
How does beta-arrestin link the GPCR to other signal transduction pathways?
GPCR-arrestin complex forms a scaffold that binds to and activates cytosolic kinases that trigger signal transduction(s)
64
What does Gq's alpha subunit bind to and activate?
phopholipase c (beta form)
65
What does phospholipase C-beta cleave?
PIP2
66
What does PIP2 get cleaved into?
IP3 and DAG
67
Lipophilic molecule that remains in the plasma membrane where it binds to and activates certain isoforms of protein kinase c
DAG
68
IP3-gated Ca2+ release channels are located where?
endoplasmic reticulum
69
What triggers the recruitment of protein kinase C to the plasma membrane
calcium
70
Protein Kinase C phosphorylates what kinds of residues
Ser/Thr
71
Which isoforms of PKC have a regulatory subunit with Ca2+ and DAG binding sites and their activation requires Ca2+, DAG, and a membrane phospholipid
Conventional Isoforms
72
A rise in cytosolic Ca2+ induces conventional isoforms of PKC to do what?
Translocate to the plasma membrane where they become activated
73
What type of ion can IP3 open channels for?
Ca2+ (IP3-gated Ca 2+ release channels)
74
What replenishes depleted Ca2+ stores in a cell?
Plasma membrane store-operated channels
75
Ca2+, when high in the ER lumen, bind to the EF hand region on what transmembrane protein?
Stromal Interacting Molecules (STIM)
76
How do STIM proteins bind to and open Orai 1 store-operated channels to bring extracellular Ca2+ into the cell?
Ca2+ dissociates from STIM when low, forming an oligomeric complex which translocates to areas of the ER close to the plasma membrane, opening store-operated channels
77
Transports Ca2+ out of the cell and into the ER; Ca is coupled to the expenditure of metabolic energy
CA2+ ATPases
78
What does PMCA stand for?
Plasma membrane Ca2+ ATPases
79
What is SERCA?
ATPases in sarcoplasmic and endoplasmic reticulum
80
An antiporter that utilizes sodium influx into the cell along its concentration gradient to move Ca2+ out of the cell.
Na+-Ca2+ Exchanger (NCX)
81
The activity of Voltage-Gated Ca2+ Channels can be modulated by... (3)
1) phosphorylation
2) G proteins
3) drugs and toxins
82
When do voltage-gated Ca2+ channels typically close
normal resting membrane potential
83
What type of channel is the IP3-gated Ca2+ release channel in the ER?
ligand-gated
84
Receptor type in which Ca2+ entering cardiac muscle cells through voltage-gated channels can further increase local Ca2+ concentration by binding to and opening to these calcium release channels in the sarcoplasmic reticulum
Ryanodine receptor
85
How many Ca2+ binding sites does calmodulin have?
four
86
What is the intrinsic enzymatic activity of calmodulin?
it has none
87
What do the four calcium binding sites on calmodulin contribute to?
positive cooperativity
88
Four examples of regulation by calmodulin
1) cyclic nucleotide phosphodiesterase
2) plasma membrane Ca2+-ATPase
3) Ca2+/CaM-dependent protein kinase II
4) myosin light-chain kinase
89
What protein kinase is found in most tissues but occurs in especially high concentrations in neurons?
Ca2+/CaM-dependent protein kinase II
90
The catalytic domain of Ca2+/CaM-dependent protein kinase II is blocked by what in the basal (inactive) state?
autoinhibitory domain
91
What allows Ca2+/CaM-dependent protein kinase II to remain active after the calcium concentration of the cytosol falls to resting levels?
Autophosphorylation
92
A mechanism of antagonistic interaction between the two pathways, cyclic nucleotide phosphodiesterase activity is enhanced by what?
Ca2+/CaM
93
How can protein kinase A interact with the Ca2+ second messenger pathway?
PKA can phosphorylate some voltage-gated Ca2+ channels
94
PKA and Ca2+/CaM-dependent kinase both phosphorylate what?
CREB
95
Transmembrane cell surface receptors that possess tyrosine kinase activity in their cytoplasmic domain
Receptor tyrosine kinases
96
Most of these receptor types are single-chain polypeptides that exist as monomers in the absence of ligand binding
Receptor tyrosine kinases
97
What receptor type consists of:
1) an extracellular domain that contains a binding site for signaling molecules
2) a single hydrophobic transmembrane alpha-helix
3) a cytoplasmic domain catalytic domain and several autophosphorylation sites
receptor tyrosine kinases
98
What happens after ligand binding with receptor tyrosine kinases?
Ligand binding induces two receptor monomers to dimerize
99
Dimerization leads to what in receptor tyrosine kinases?
autophosphorylation. This area is called the activation loop
100
Fully active domains of receptor tyrosine kinases phosphorylate... (2)
1) cytosolic segments of the receptor dimer. These phosphotyrosines act as docking sites for intracellular signaling molecules
2) intracellular signaling molecules, transmitting the signal further downstream
101
Insulin and IGF-1 receptors are submembers of what category?
Receptor tyrosine kinases
102
Structure of insulin receptor (its subunits)
two external alpha subunits and 2 transmembrane beta units, bound together by disulfide bridges
103
Where is the ligand binding site on the insulin receptor? where is the tyrosine kinase domain?
Ligand binding site - alpha
| Tyrosine kinase domain - beta
104
What is one of the major targets of insulin receptor tyrosine kinase activity?
Insulin Receptor Substrates (IRS)
105
What do the phosphotyrosine residues of IRS do?
Serve as a docking site for other intracellular signaling proteins
106
Various intracellular signaling proteins (multiple) can recognize and dock with phosphotyrosines on the IRS by means of what domain?
Their SH2 domains
107
What is a critical negative regulator of insulin and IFG signaling (important to prevent tumor formation and metabolic abnormalities)
Phosphotyrosine phosphatases
108
Purpose of intracellular signaling proteins binding to phosphotyrosines on the RTK? (3)
1) localizes them to the plasma membrane
2) enables them to interact with other proteins that are associated with the receptor
3) activates the signal transduction pathways to which the intracellular signaling proteins are coupled
109
Besides SH2 domains, intracellular signaling proteins can associate with receptor phosphotyrosines by means of which domain?
Phosphotyrosine binding domains (PTB)
110
Highly conserved region of about 100 amino acids on intracellular signaling proteins
SH2
111
PLC-γ (phospolipase C isoform gamma) can be activated by...
receptor tyrosine kinases
112
Negative regulator of Ras
GAPs (GTPase-activating protein), because they promote GTP hydrolysis
113
Positive regulator of Ras
GEFs (Guanine nucleotide exchange factor) because they promote the release of GDP, which is then replaced by GTP
114
Ras inactive/off state
GDP bound
115
Ras active/on state
GTP bound
116
What activates the Ras/MAP kinase pathway
receptor tyrosine kinases
117
Cell signaling pathway playing an important role in regulating cell proliferation and differentiation
MAP kinase pathway
118
Raf, MEK, and MAPK are kinases activated in what pathway?
MAP (mitogen-activated protein) kinase pathway
119
What makes up the adaptor/guanine exchange factor complex connecting the receptor tyrosine kinase and activating Ras?
GRB2/Sos
120
Virtually all receptor tyrosine kinases are capable of activating which pathway?
Ras/MAP pathway
121
MAPK inducts gene transcription by phosphorylating which two transcription factors?
SRF (indirectly through p90RSK) and TCF
122
Family protein/peptide signaling molecules that play a major role in regulating the proliferation and differentiation of blood cells and cells of the immune system.
Cytokines
123
Cytokine receptors are bound to what in their cytoplasmic domain?
Janus Kinase (JAK)
124
JAKs phosphorylate which types of residues
Tyrosine
125
Structure of cytokine receptors
Typically function as homodimers. The receptor dmer may be preformed before ligand binding or form in response to ligand binding
126
True or false; JAK protein kinases have activation loops
true
127
STAT proteins (Signal Transduction and Activation of Transcription) are major targets of _____
JAKs
128
What are STAT proteins?
Transcription factors located in the cytoplasm
129
These transcription factors have an SH2 domain and require tyrosine phosphorylation for activation
STAT proteins
130
How do STAT proteins activate gene transcription
They're first phosphorylated, form dimers, and translocate to the nucleus
131
Inhibits receptor tyrosine kinase activity by phosphorylating specific serine or threonine residues in the cytosolic domain of the receptor
Protein Kinase C
132
Prolonged stimulation of certain tyrosine kinase and cytokine receptors by their respective ligands can reduce the number of cell surface by....
increasing the rate of receptor-mediated endocytosis
133
Which type of signaling protein can, when bound to the activated receptor, induce ubiquitination
SH2
134
SHP1, a phosphotyrosine kinase, acts on which receptor?
Erythropoietin receptor
135
One (of the two) SH2 domains binds to and inactivates the phosphatase domain of SHP1. What state is the cell in (stimulated or unstimulated)?
Unstimulated
136
When active, the blocking SH2 domain of SHP 1 docks with the phosphotyrosine residue on the erythropoeitin receptor near the catalytic domain of ____. The exposed phopshatase domain of SHP1 removes a phopshate group in the activation loop, reducing the catalytic activity of ____ (both blanks are the same)
JAK
137
Phosphatidylinositol 3-phosphate (PI 3-phosphate) does what?
activates many cytoplasmic protein kinases
138
PI 3-kinase is able to be recruited to the plasma membrane by which two activated receptors
Receptor tyrosine kinases and cytokine receptors
139
What catalyzes the addition of 3-phosphate to phosphoinositide substrates in the plasma membrane to form PI 3-phosphates
PI 3-kinase
140
PI 3-phosphates function as _____ sites for certain signal transduction proteins
docking sites
141
Plextrin homology (PH) domains bind what with high affinity?
3-phosphates
142
Akt is also called
Protein Kinase B
143
What kind of kinase is PKB/Akt
Serine / Threonine
144
An important kinase that binds to PI 3-phosphates in the plasma membrane is....
Akt aka protein kinase B
145
The PH domain of PKB is bound to the catalytic domain in what state
unstimulated
146
During stimulation of the cell by a signaling molecule, partial activation is achieve by what binding what
PH domain of PKB binds to 3-phosphate groups
147
Full activation of PKB requires which two additional kinases
PDK1 and PDK2
148
Fully active PKB plays an important role in what two things
1) promoting cell division and survival
| 2) regulation of metabolism
149
Members of the FOXO family of transcription factors are major targets of ___
Akt (PKB)
150
Cytosolic chaperons called 14-3-3 proteins bind Akt (PKB) phosphorylated ____ transcription factors and keep them in the cytosol to stop them from inducing transcription
FOXO transcription factors
151
Transcription factor involved in transcription of numerous genes encoding proteins that are involved in inflammatory and immune responses
NF-kB
152
What is an example of a gene transcription signaling pathway being regulated by the ubiquitin-mediated degradation of an inhibitor protein
NF-kB signaling pathway (inhibitory protein = IκBα)
153
Blocks the translocation of NF-kB to the nucleus
IκBα
154
When the cell is subjected to viral infection, ionizing radiation or is exposed to a mediator of inflammation this kinase is activated (NF-kB signaling pathway)
I-κB kinase (phosphorylates two serine residues on IκBα)
155
What binds to phosphorylated IκBα to trigger its degradation by proteosomes
E3 ubiquitin ligase
156
Protein products of the NF-kB pathway (4)
1) phospholipase A2
2) cyclooxygenase
3) NO synthase
4) cytokines (such as TNFα and interleulin-1)
157
One of the genes that NFkB regulates is the gene for IκB. This makes it what type of feedback loop?
Negative. IκB returns activated NF-kB to the cytosol
158
Nitric Oxide (NO) is made by the deamination of ______ in a reaction catalyzed by the enzyme NO Synthase
arginine
159
What does NO released from endothelial cells do as an example of paracrine signaling?
Relaxation of smooth muscle cells in blood vessels
160
The NO released from endothelial cells in response to acetylcholine stimulation diffuses into the underlying vascular smooth muscles cells and activates a soluble form of what enzyme?
Guanylyl cyclase
161
The rise in ____ levels promotes vasorelaxation (related to NO signaling)
cGMP
162
Vasorelaxation is promoted by which kinase
cGMP-Dependent Protein Kinase
163
What do receptors for thyroid hormones, steroid hormones, vitamin D3 and retinoids function as when bound by their ligand
transcription factors
164
DNA-binding fingers are featured in pairs in what receptor
intracellular receptors
165
What is the hinge region in intracellular receptors
a flexible region between the DNA-binding domain and Ligand binding domain
166
In the absence of hormone binding, unoccupied steroid hormones are part of what?
multi-protein chaperone complex that includes heat shock proteins
167
Where do steroid hormone receptors bind to the DNA
Steroid-response elements (SRE)
168
In hormone-dependent activation of gene transcription, hormone-bound receptor dimers recruit a complex of...
coactivator proteins (some of which possess histone acetyltransferase activity!)
169
Androgen receptor antagonist
flutamide
170
Progesterone receptor antagonist
RU486
171
True or False; Thyroid Hormone Receptors tend to bind tightly to DNA even in the absence of hormone binding
true
172
Binding site for Thyroid Hormone Receptors on DNA
Thyroid Response elements
173
True or False; Steroid hormone receptors tend to bind tightly to DNA even in the absence of hormone binding
false
174
Which hormone receptor family does not form complexes with heat shock proteins when unbound by hormone
Thyroid Hormone Receptor Family
175
Thyroid Hormone Receptors heterodimer with which receptor
RXR receptor
