cell signaling Flashcards
1
Q
where can cells receive signals from
A
from the environment and other cells
2
Q
how do unicellular organisms communicate
A
through the release of signaling molecules into the environment
3
Q
how do multicellular organisms communicate
A
through extracellular signaling molecules that function within the organism
4
Q
list 4 examples of extracellular signaling molecules used in multicellular organisms
A
proteins, amino acids, steroids, dissolved gases
5
Q
what are two types of receptors that a cell may have
A
cell-surface or intracellular receptor
6
Q
what is endocrine signaling
A
signaling molecule is released into the bloodstream and acts at a distance from where it is made
7
Q
in endocrine signaling, does the signal molecule act close to or far away from the site where it’s made
A
far away
8
Q
in endocrine signaling, where is the signal molecule released
A
into the bloodstream
9
Q
what is paracrine signaling
A
signaling molecule affects a cell that is in close proximity
10
Q
what does the signal molecule affect in paracrine signaling
A
another cell that’s close by
11
Q
does paracrine signaling occur close by or far away
A
close by
12
Q
what is synaptic signaling
A
occurs in neurons
13
Q
what is autocrine siganling
A
cell releases a molecule that it responds to
14
Q
what is an example of a signal molecule released in autocrine signaling
A
growth factors
15
Q
what is contact-dependent signaling
A
signal remains bound to the surface of the cell and contact to the target cell is required
16
Q
in extracellular signaling, describe what happens in the cell once the signal molecule/ligand binds to the receptor
A
it activates one or more signaling pathways, and this will alter the activity of an effector protein, and the effector protein will cause changes in the cell
17
Q
what two things might an intracellular siganling molecule be
A
a chemical or a protein
18
Q
how do protein signaling molecules behave
A
like molecular switches
19
Q
what are chemical signaling molecules called
A
second messengers
20
Q
list some examples of second messengers
A
Ca2+ ions, cGMP, cAMP, DAG, IP3
21
Q
are second messengers proteins?
A
no, they’re nonprotein
22
Q
how heavy are second messengers
A
low molecular weight
23
Q
list two advantages of second messengers
A
they can diffuse through the cytosol faster than proteins, and they facilitate amplification of the extracellular signal
24
Q
explain how proteins may act as molecular switches
A
they can switch into an active or inactive form as a result of their phosphorylation state
25
what two things mediate phosphorylation
kinases and phosphatases
26
what do kinases do
phosphorylate specific amino acid residues
27
what do phosphatases do
remove specific phosphate groups
28
name the two types of protein kinases that animal cells contain
protein tyrosine kinase (PTK) and Ser/Thr kinases
29
other than phosphorylation state, binding of ____ controls the active and inactive forms of proteins
GTP/GDP
30
T or F: a signal molecule can have different effects on different target cells
true
31
state the two forms of cellular responses
fast and slow responses
32
what is a fast cellular response
changes in the activity or function of proteins that already exist in the cell
33
what is a slow cellular response
changes in the amounts of specific proteins produced by a cell through changes in gene expression
34
how many domains do cell surface receptors have
3
35
name the 3 domains of cell surface receptors
extracellular, transmembrane, and intracellular domain
36
T or F: each receptor generally only binds a single signaling molecule or a group of structurally related molecules
true
37
name the 3 main classes of cell surface receptors that mediate signal transduction
ion-channel-coupled receptors
G protein-coupled receptors
enzyme-coupled receptors
38
what is the most numerous type of receptor
GPCRs
39
list some different ligands that GPCRs respond to
photons, odorants, tastants, hormones, NTs, and chemoattractants
40
what percentage of all prescription drugs target the GPCR superfamily
30%
41
what does salmeterol do
acts as an agonist for epinephrine; it binds to GPCRs on smooth muscle cells of the airway to facilitate respiration
42
what does the GPCR activate
a G protein
43
list the basic structure of a GPCR
7 transmembrane alpha helical regions
4 extracellular segments
4 cytosolic segments
44
how many extracellular and cytosolic segments does a GPCR have
4 each
45
what type of helices do GPCRs have
alpha helices
46
describe how the helices of GPCRs are situated at the membrane
they span the membrane; transmembrane helices
47
how many transmembrane alpha helices do GPCRs have
7
48
why are G proteins called G proteins
because they bind GDP or GTP
49
name the two classes of G proteins used in signaling
heterotrimeric and monomeric
50
which type of G protein, heterotrimeric or monomeric, associates with GPCRs
heterotrimeric
51
T or F: heterotrimeric G proteins act as molecular switches
true
52
what controls the activation state of G proteins
GDP vs GTP bound to it
53
what is the G protein bound to in the inactive state
GDP
54
in regards to G protein activation, what converts the GDP to GTP
GEFs
55
what is a GEF
guanine nucleotide exchange factor
56
what is the G protein bound to in its active state
GTP
57
once the G protein is in its active state, what happens to the signal
the signal will leave and bind to activate other proteins
58
in regards to G protein inactivation, what converts the GTP to GDP
GAP
59
what is GAP
GTPase activation protein
60
in the conversion of GTP to GDP, where does the GTPase come from
its intrinsic GTPase of the G protein
61
T or F: in the active conformation, the G protein can bind to other proteins
true
62
T or F: in the inactive conformation, the G protein can bind to other proteins
false; it can only bind to other proteins while in the active state
63
list the 3 subunits of the heterotrimeric G protein
alpha, beta, gamma
64
which subunit of heterotrimeric G protein contains the GTPase
alpha
65
which subunits of the heterotrimeric G protein are always bound together
b and Y
66
which subunits of the heterotrimeric G protein are bound to the PM via covalently linked lipids
a and y
67
how are the a and y subunits of the heterotrimeric G protein bound to the PM
through covalently linked lipids
68
which subunit of the heterotrimeric G protein gives it its specificity in terms of what it activates
the a subunit
69
how many families of G protein are there based on the a subunit
4
70
which family of G proteins activates adenylyl cyclase
Gs
71
how does a GPCR become active
a signal molecule will bind to it
72
once the GPCR is active, what can it do
bind the G protein
73
list one target of G proteins
adenylyl cyclase
74
where is adenylyl cyclase located
on the PM
75
describe how G proteins can activate/inactivate ion channels in the form of regulating blood glucose
glucagon binds to GPCR present on liver cells, liver breaks down glycogen into glucose = blood glucose levels raise, homeostasis will eventually be reached, then when blood glucose levels decrease the alpha cells of the pancreas will release glucagon and this will repeat
76
is the regulation of blood glucose levels a fast or slow protein response
fast protein response
77
how is adenylyl cyclase stimulated
stimulated by the active Ga subunit of the G protein
78
what does adenylyl cyclase produce
cAMP (a second messenger)
79
how does adenylyl cyclase produce cAMP
ATP --> cAMP
80
how many catalytic domains does adenylyl cyclase have
2
81
which side of the PM contains the 2 catalytic subunits of adenylyl cylase
cytosolic side
82
what does cAMP activate
protein kinase A (PKA)
83
why can't the conversion of ATP to cAMP in adenylyl cyclase go on forever?
the binding of the G protein to adenylyl cyclase enhances the intrinsic GTPase activity of the Ga subunit resulting in its inactivation
84
what amino acids does PKA add a phosphate to
serine or threonine
85
how many subunits does PKA have
2
86
name the 2 PKA subunits
catalytic and regulatory
87
describe the mechanism of PKA activation
cAMP binds to the regulatory subunit = conf change = catalytic sites dissociate = PKA is active and can phosphorylate residues
88
describe the orientation of the PKA subunits when PKA is inactive
regulatory and catalytic subunits are intact
89
describe the orientation of the PKA subunits when PKA is active
catalytic subunits have dissociated
90
where is PKA located
in the liver
91
what two enzymes does PKA target in the liver
glycogen synthase
glycogen phosphorylase kinase (GPK)
92
what does glycogen synthase do
converts glucose to glycogen
93
what happens when PKA phosphorylates glycogen synthase
it inhibits its catalytic activity, so glucose is not converted to glycogen
94
what happens when PKA phosphorylates glycogen phosphorylase kinase
it activates it = it can phosphorylate glycogen phosphorylase
95
what does glycogen phosphorylase kinase add a P to
glycogen phosphorylase
96
what does glycogen phosphorylase do
stimulates the breakdown of glycogen
97
what is produced when glycogen phosphorylase breaks down glycogen
glucose 1-phosphate
98
what happens to glucose 1-phosphate in the liver
it's converted to glucose 6-phosphate, and then to glucose by phosphatase
99
what enzyme converts G6P to glucose in the liver
phosphatase
100
how is glucose transported across the PM of liver cells into the bloodstream
by the transmembrane carrier GLUT2
101
what is GLUT2
a transmembrane carrier that brings glucose into the blood from liver cells
102
how many G proteins can 1 activated receptor activate
100
103
how many adenylyl cyclase molecules can each G protein activate
1
104
how many cAMPs can each AC make
100
105
how many PKAs does each cAMP activate
1
106
how many targets can each PKA activate
10
107
how many targets can glycogen phosphorylase kinase activate
10
108
how many G1P molecules does each glycogen phosphorylase create from glycogen
100
109
how many glucose molecules are made from one signal
10^8 glucose molecules
110
list some targets of PKA other than enzymes
ion channels, chromosomal proteins (ie Histone H1), and transcription factors (ie CREB)
111
what is CREB
a transcription factor
112
what is the name of CREB
CRE-binding protein
113
what is the name for CRE
cAMP response element
114
what is the cAMP-response element
a cis-reg sequence
115
what does CREB do
controls genes that contain a cis-reg sequence (CRE)
116
what genes have the CRE as part of their gene-control region?
genes involved for the enzymes of gluconeogenesis
117
when might we need increased production of the genes that code for the GNG enezymes
in conditions of prolonged fasting
118
is production of the GNG genes in conditions of prolonged fasting a slow or fast response
SLOW
119
describe how the GNG proteins get produced, starting at PKA activation
the catalytic subunits of PKA translocate to the nucleus, and then PKA phosphorlyates CREB at Ser 113. P-CREB binds as a dimer onto CRE, and it also binds a coactivator (CBP/300). This results in transcription of the target genes
120
at which site does PKA phosphorylate CREB
Ser 113
121
in what form does CREB bind to CRE
as a dimer
122
what co-activator binds to CREB when it's bound to CRE
CBP/300
123
what is receptor inactivation
a mechanism of desensitization frequently used by GPCRs
124
in receptor inactivation, how does the GPCR become inactivated
via phosphorylation
125
describe how desensitization occurs in GPCRs
the activated GPCR activates a GPCR kinase (GRK) located in the cell, and this phosphorylates multiple sites on the GPCR. this allows the protein Arrestin to come in and bind to the receptor
126
in desensitization, what protein comes in to bind to the GPCR once the GPCR has been phosphorylated by a GRK
Arrestin
127
what are 2 outcomes of a GPCR once it's desensitized
it can be recycled back to the cell surface or be degraded in lysosomes
