Test 3 Flashcards
(210 cards)
1
Q
What type of cell is this?
among the most abundant cells: cover the skin, line the organs, body
cavities and blood vessels. Their highly specialized histologic features are critical
for their physiological functions in different organs
A
epithelial cell
2
Q
What are fibroblasts?
A
a type of cell that contributes to the formation of connective tissue;
secretes collagen and other proteins into the extracellular matrix
3
Q
How does the epithelial tissue handle mechanical stress?
A
mechanical stresses are transmitted from cell to cell by cytoskeletal filaments anchored to cell-matric and cel-cell adhesion sites
4
Q
How are the cytoskeletons of the cells in epithelial tissue linked?
A
from cell to cell by anchoring junctions
5
Q
In epithelial tissue, what does the cell-matrix bond the epithelial tissue to?
A
basal lamina and connective tissue beneath it
6
Q
What is the basal lamina?
A
is the thin mat of extracellular matrix proteins (primarily laminin) that
separates epithelial sheets from connective tissue; sometimes called the basement
membrane
7
Q
What are examples of connective tissue?
A
bone or tendon
8
Q
How does connective tissue handle mechanical stress?
A
the extracellular matrix directly bears mechanical stresses of tension and compression
9
Q
In connective tissue, how do cells have connections to the matrix?
A
through integrin receptors
10
Q
What is responsible for the cell’s spatial organization and mechanical properties?
A
cytoskeleton
11
Q
What are actin filaments?
A
they determine the shape of the cell’s
surface and are necessary for
locomotion
12
Q
What are microtubules?
A
they Determine the positions of
membrane-enclosed organelles
and direct intracellular vesicular
transport
13
Q
What are intermediate filaments?
A
They bear tension and maintain cell shape
14
Q
Information about actin filaments
A
Involved in cell shape and motility
Think: lamellipodia, filopodia, and contractile rings during cytokinesis
Highly dynamic — grows/shrinks rapidly
Often found just under the plasma membrane (cortical actin)
-uses ATP
15
Q
information about microtubules
A
Highways of the cell → move vesicles, organelles, and chromosomes
Grow from centrosome (MTOC) and radiate outward
Show dynamic instability → rapid growth and shrinkage
Make up mitotic spindles, cilia, and flagella
-uses GTP
16
Q
information about intermediate filaments
A
Stable, strong, and long-lasting
Provide tensile strength (e.g., keep cells from being pulled apart)
Found in areas with mechanical stress (e.g., skin, muscle, neurons)
Examples: Keratin (epithelial cells), neurofilaments (neurons), lamins (nuclear envelope)
17
Q
Epithelial cells are polar or nonpolar?
A
polar
18
Q
What are the three regions of a epithelial cell?
A
apical, basal, and basolateral
19
Q
What are tight junctions?
A
seals neighboring cells together in an epithelial sheet to prevent leakage of extracellular molecules between them:
20
Q
What junction helps polarize epithelial cells?
A
tight junction
21
Q
What are adherens junction?
A
joins an actin bundle in one cell to a similar bundle in a neighboring cell
22
Q
What are desmosome?
A
they join the intermediate filaments in one cell to those in a neighbor
23
Q
What are gap junctions?
A
they form channels that allow small, intracellular, water-soluble molecules, including inorganic ions and metabolites, to pass from cell to cell
24
Q
What are hemidesmosome?
A
they anchor intermediate filaments in a cell to the basal lamina
25
What junctions are junctional complex proteins?
tight junctions, adherens junctions, and desmosomal junctions
26
What are junctional complex proteins?
they act as a coordinated unit to maintain tissue polarity, they depend on each other for their positioning
27
What are anchoring junctions?
they transmit stress, provide structure and maintain tissue integrity
28
What are considered anchoring junctions?
adheren junctions, desmosome junctions, and hemidesmosome junctions
29
What surfaces do tight junctions seal gaps between?
apical and basolateral surfaces
30
What proteins are involved in tight junctions?
claudin and occludin
31
Why is it important
for the epithelia to
form a selectively
permeable
barrier?
The epithelial cells lining the gut lumen need to form a selectively
permeable barrier because it allows the absorption of essential nutrients
from food while simultaneously preventing harmful substances like bacteria
and large molecules from entering the bloodstream, maintaining a crucial
balance between nutrient uptake and protection against pathogens and
toxins within the digestive tract
32
How do adherens junctions link epithelial cells?
through thousand transmembrane cadherin molecules (they are linked to the actin cytoskeleton)
33
What junction forms the adhesion belt?
adherens junctions
34
What helps the cadherins contract and provide the motile force for folding of epithelial cell sheets?
myosin and motor proteins
35
Why is contraction of epithelial sheets?
it is important for folding into tubes, vesicles and other related structures during development
36
How do desmosomes provide mechanical strength?
through linkage to intermediate filaments
37
What is desmosomes role?
perserving tissue integrity
38
How do hemidesmosomes link cell to protein in basal lamina?
through integrin receptors/
39
What transmembrane protein in gap junctions allows a channel to form between two cells?
connexon
40
What do the specialized gap junctions in cardiac cells allow for?
rapid transmission of electrical impulses between cells
41
What does the gap junctions in cardiac cells ensure?
coordinated muscle contractions through the heart by facilitating the flow of ions between adjacent cells
42
How are the cytoplasm of adjacent plant cells are connected?
plasmodesmata
43
What are plasmodesmata?
numerous cytosolic channels that pass between adjacent plant cell walls to connect their cytoplasm, and enable transport of materials from cell to cell, and thus throughout the plant
44
What are cell walls composed of?
cellulose and polysaccharides
45
What allows plant cells to not anchoring junctions to hold the cells in place?
cell walls of adjacent cells are firmly cemeted to those of neighbors
46
How do cells interact with extracellular matrix in tissue?
through integrin receptors
47
What is the ECM constructed of?
proteoglycans, fibrous proteins, and glycoproteins
48
What do fibroblasts in the ECM make?
they organize components of the ECM
49
What does collagen provide the ECM?
tensile strength
50
How are epithelial cells separated from the underlying tissue?
basal lamina
51
What is collagen made of?
three interwined polypeptide chains
52
How are collagen chains arranged?
in fibers
53
how are collagen chains organized?
fibroblasts
54
What are fibronectin?
molecules are glycoproteins in the ECm that bind to collagen fibrils outside the cell membrane
55
What do integrin receptors transmit?
tension across the plasma membrane
56
What are the two subunits of integrins?
Alpha (α) and Beta (β)
57
What triggers integrins to switch from inactive to active form?
Binding to an extracellular matrix molecule (like fibronectin) or intracellular adaptor proteins.
58
What is the inactive form of integrin like?
Folded conformation with subunits close together.
59
What is the active form of integrin like?
Extended conformation where subunits are separated and can bind to both ECM and cytoskeleton.
60
What is "outside-in activation" of integrins?
An extracellular ligand binds, causing integrin to unfold → reveals intracellular binding sites → links to actin filaments.
61
What is "inside-out activation" of integrins?
Intracellular adaptor proteins bind the β subunit → causes integrin to unfold → enables binding to ECM.
62
What is the function of integrins in the cell?
They form reversible mechanical linkages across the membrane, connecting ECM to the cytoskeleton.
63
How does integrin activation support cell movement?
Activation stabilizes the connection between the ECM and actin filaments, allowing traction and migration.
64
Integrin activation is an example of what kind of linkage across the membrane?
Reversible mechanical linkage
65
What are integrins?
Integrins are transmembrane proteins that connect the outside of the cell (ECM) to the inside (cytoskeleton).
66
What forms at the leading edge of a migrating cell?
Actin filaments polymerize to push the membrane forward.
67
What is a focal adhesion?
A cluster of integrins that links the actin cytoskeleton to the ECM (like fibronectin).
68
What happens if actin doesn’t interact with focal adhesions?
Actin filaments get pushed backward and don’t generate forward movement.
69
What allows a cell to pull itself forward during migration?
Active integrins + myosin-mediated tension at focal adhesions.
70
What is the role of fibronectin in cell migration?
It binds integrins, anchoring the cell to the ECM and linking it to the actin cytoskeleton.
71
What are glycosaminoglycans (GAGs)?
Long, negatively charged sugar chains that attract water and resist compression.
72
What is a proteoglycan?
A protein with GAG chains attached — forms a hydrated gel that fills ECM space.
73
What is the difference between a GAG and a proteoglycan?
GAG = sugar chain; proteoglycan = protein + GAGs
74
What kind of tissue has high GAG content?
Soft, jelly-like tissue (e.g., inside of the eye)
75
What kind of tissue has low GAG content?
Hard, stiff tissue (e.g., bone)
76
What components of the ECM resists compressive forces on the matrix?
proteoglycans
77
What component of the ECM strenthen and help organize the matrix and provide resiliency?
fibrous proteins
78
What component of the ECM help cells migrate, setlle and differentiate in appropriate locations?
matrix glycoproteins
79
What is cell signaling?
how cells communicate to each other
-how cells transmit and recieve infromation so they can respond appropriately to the environemtn
80
What are the four steps of cell signaling?
1. a signal is sent from a cell in response to an environmental or molecular cue
2. the signal is recieved by a cell containing the specific receptor for the signal
3. the signal is interpreted/transduce by the receiving cell
4. the cell responds in one or more ways to the signal
81
What are the two ways a signal could be sent?
a cell could release a molecular cue or the environemtal conditions could provide the molecule that is being detected
82
Is the receptor that recognizes the signal general or specific?
specific
83
What does the receptor have to undergo in response to binding the signal?
a conformation change
84
Are receptors inside or at the cell surface?
they can be both
85
What is the interpretation step of the signal called?
transduction
86
When a signal is interpreted, how does the signal get across the plasma membrane?
activating specific internal responses
87
True or False: A cell could have multiple responses to a signal
True
88
What is autocrine signaling?
when a cell releases a ligand that is received by its own receptor
89
What is signaling across gap junctions?
the transfer of signaling molecules communicates the current state of the cell that is directly next to the target cell; this allows a group of cells to coordinate their response to a signal that only one of them may have recievdd
90
What do plants have they allow them to form channels between adjacent cells, which makes the entire plant into a giant communication network
plasmodesmata
91
What is paracrine signaling?
cells secrete signal molecules into the extracellular fluid/matrix that can act locally on adjacent cells (short-range signals)
92
What is endocrine signaling?
long range signaling that involves hormones traveling through the bloodstream to act on target cells
93
In endocrine signaling what acts as their signaling molecules?
hormones
94
True or False: Hormones act at very low concentrations due to high specificity of receptor binding
true
95
What is juxtacrine signaling?
signal molecules remain bound to surface of signaling cell and influence only cells that contact it
96
What is neuronal signaling an example of?
paracrine signaling
97
What is the site of nucleus and organelles in Neurons?
cell body
98
What are dendrites?
branched extensions from the cell body that receive messages from other neurons at specialized junctions called synapses
99
What are axons?
variable length extension from the cell body that allows the electrical signal to travel to specialized endings called axon terminals (synapse on other neurons)
100
What are neurotransmitters?
chemicals released at axon terminals that allow signals to be communicated to target cells
101
What type of cells release the neurotransmitter?
presynaptic
102
What type of cells have the receptors that bind to the neurotransmitter?
postsynaptic
103
What is the distance called between the presynaptic and postynaptic cell called?
the synaptic gap
104
True or False: receptors in the synapse are to be low affinity
True
105
What types of molecules function as signals?
-steroids
-amines
-peptides
106
What are characteristics of steriods?
-4 ring structure
-hydrophobic
-intracellular binding to receptor
107
What are characteristics of amines?
-contain amine group
-hydrophilic or hydrophobic
-small
108
What are characteristics of peptides?
-few to hundred of amino acids
-hydrophilic
-extracullar binding to receptor
109
What are the characteristics of a signaling molecule that can cross the outer membrane to enter the interior of target cells?
small and hydrophobic
110
What type of signaling molecule is recognized by cell surface receptors?
large and hydrophilic
111
True or False: Gases can act as intracellular signaling molecules?
True
112
How do hydrophobic signal move across the cell membrane?
diffusion
113
What are the steps for hydrophobic signals entering the cell?
1. crosses through diffusion
2. binds to intracellular receptor (conformational change)
3. receptor ligand complex moves into the nucleus
4. binds to a specific sequence of DNA
5. gene transcription
114
What are type I intracellular receptors?
they are anchored in the cytoplasm of a cell by chaperone proteins. (kept in an inactive state)
115
With type I intracellular receptors the ligand bind results in what?
a confromational change in the receptor that releases the chaperone proteins.
116
In type I receptors what does the conformational change expose?
a nuclear localization sequence and a DNA-binding site on the receptor protein
117
In type I receptors how does the receptor-ligand complex move into the nucleus?
through nuclear pores
118
When the receptor-ligand complex is in the nucleus, where does it bind?
specific regulatory regions of the chromosomal DNA and promotes intiation of transcription of one or more genes
119
Where are type II intracellular receptors located?
in the nucleus
120
What are type II intracellular receptors bound to in their inactive state?
co-repressors
121
When the co-repressors proteins are released upon ligand binding, what are the type II intracellular receptor allowed to do?
they are allow to bind to DNA and modulate gene expression
122
What is an advantage of intracellular receptors?
they directly influence gene expression without having to pass the signal on to other receptors or messengers
123
What are the steps for hydrophilic signals bind to cell surface receptors to initiate signal transduction?
1. signal molecule(first messenger) binds to the extracellular side of a transmembrane receptor
2. conformational change in the intracellular domain of the receptor
3. signal is relayed by different intracellular signaling proteins (second messengers) through a signal cascade
4. effector proteins produce some type of response`
124
What are first messengers?
the extracellular signals whose binding by receptor proteins in the plasma membrane initiates a signaling cascade
125
What are second messengers?
intracellular signaling molecules, generated in large numbers in response to receptor activation
126
What are effector proteins?
intracellular targets that implement the change in cell behavior
127
What is signal transduction?
the events that convert one type of signal to another type of signal
128
What does the speed of a response to an extracellular signal depend on?
-the nature of the target cell's response
129
rapid responses occur through changes in ______
phosphorylation
130
What are protein kinases?
enzymes that covalently add one or more phosphate groups to the signaling protein. (activate or inactivate a target protein)
131
What are protein phosphatases?
enzymes which remove the phosphate groups
132
Where are phosphates often added?
serine, threonine or tyrosine
133
If there is phosphorylation at serine or threonine it often ____ enzymes?
activates
134
Where is the energy required to drive this phosphorylation cycle dervied from?
free energy of ATP hydrolysis
135
What is amplification?
when the signal is relayed and activates a molecule, a single molecule can activate many other molecules
136
What is a scaffold protein?
interacts with the receptor and holds together other relay molecules in close proximity (speeds up transduction)
137
What are the three main types of cell surface receptors?
1.) Ion-channel-coupled receptors
2.) enzyme coupled receptors
3.) G-protein-coupled receptors
138
When a ligand binds to the extracellular region of an ion-channel-coupled receptor, what happens that allows ions to go through?
a conformational change in the protein's structure
139
What is an example of an Ion-channel-coupled receptor?
Nicotinic acetylcholine receptor
140
What are nicotinic acetlcholine receptors (nAChRs) made up of?
five subunits that assemble into pentamers
141
What are the key features and activation mechanism of enzyme-coupled receptors?
Structure:
Large extracellular and intracellular domains
Single membrane-spanning alpha-helix
Function:
Activated by ligand binding (typically small peptides like insulin or growth hormones)
Ligand binding promotes receptor dimerization
Activation Mechanism:
Dimerization activates the intracellular domain, which:
Has intrinsic kinase activity, OR
Is associated with a kinase
Leads to phosphorylation of downstream target proteins → Signal transduction
142
What are Receptor Tyrosine Kinases (RTKs)?
RTKs are a type of enzyme-coupled receptor involved in cell signaling. They have kinase domains that become active upon ligand-induced dimerization.
143
What is the state of RTKs in the absence of ligand?
In the resting state, RTKs are not dimerized, and their kinase domains are inactive.
144
What happens when a ligand binds to an RTK?
Ligand binding triggers dimerization of the RTK, which activates the kinase domains and initiates cross-phosphorylation.
145
What is cross-phosphorylation in RTKs?
Each RTK in the dimer phosphorylates tyrosine residues on the other receptor, primarily outside the kinase domain. This creates docking sites for intracellular signaling proteins.
146
What do phosphorylated tyrosine residues on RTKs do?
They act as high-affinity docking sites for specific signaling proteins, allowing the formation of a signaling complex.
147
How are signaling proteins activated after docking on RTKs?
Docked signaling proteins may be activated by:
Phosphorylation by the RTK
Conformational changes upon binding
Close association with other signaling proteins
148
What can docked signaling proteins do after binding?
They can become part of the signaling cascade and/or recruit other proteins, helping relay and amplify the signal within the cell.
149
What is Ras, and what type of protein is it?
Ras is a small monomeric GTPase that acts as a molecular switch. It toggles between an inactive GDP-bound form and an active GTP-bound form.
150
How is Ras activated downstream of an RTK?
GEF (guanine nucleotide exchange factor) docks onto the activated RTK.
GEF promotes the exchange of GDP for GTP on Ras, activating it.
151
What happens to Ras once it is activated?
A lipid tail on Ras is exposed, allowing it to anchor to the plasma membrane.
It diffuses laterally and activates other signaling proteins.
152
What type of downstream signaling cascade is commonly activated by Ras?
Ras activates the MAP kinase cascade, a series of kinases that phosphorylate each other to amplify and relay the signal.
153
How is Ras signaling turned off?
A GTPase-activating protein (GAP) stimulates Ras to hydrolyze GTP to GDP, returning it to the inactive state.
154
What role does the RTK play in Ras activation?
RTKs act as scaffolds, allowing GEFs and other proteins to dock in proximity to Ras for efficient activation.
155
How is Ras activation similar to GPCR signaling?
Like G-proteins, Ras:
Is GTP-bound when active
Has a lipid tail for membrane attachment
Functions as a switch
Has short-lived activation due to GTP hydrolysis
156
What are the two main types of GTP-binding proteins involved in cell signaling?
Small monomeric GTPases (e.g., Ras)
Large trimeric G-proteins (activated by GPCRs)
157
What is the "on" vs. "off" state of GTP-binding proteins?
ON = GTP-bound (actively signaling)
OFF = GDP-bound (inactive)
158
What is intrinsic GTPase activity?
It’s the ability of a GTP-binding protein to hydrolyze GTP to GDP, switching itself off.
159
What do GTPase-activating proteins (GAPs) do?
GAPs increase the rate of GTP hydrolysis, helping drive the protein into the inactive (GDP-bound) state.
160
What do Guanine Exchange Factors (GEFs) do?
GEFs activate GTPases by promoting the release of GDP and facilitating binding of GTP.
161
What is a common role of small monomeric GTPases like Ras?
They relay signals from various cell surface receptors, including RTKs, and help activate downstream signaling pathways.
162
What is the role of large trimeric G-proteins?
They relay signals from G protein-coupled receptors (GPCRs) and activate downstream effectors.
163
What structural feature defines GPCRs?
GPCRs have seven transmembrane domains that span the lipid bilayer.
164
How are GPCRs activated?
An extracellular signal (ligand) binds the receptor, causing a conformational change that activates a trimeric GTP-binding protein (G-protein) inside the cell.
165
Where do ligands bind on GPCRs?
Large ligands bind to extracellular domains.
Small ligands bind within a pocket formed by transmembrane segments deep in the membrane.
166
What happens after a GPCR binds its ligand?
The receptor changes shape and activates an associated trimeric G-protein, which then acts on downstream signaling targets.
167
Can one extracellular signal activate more than one GPCR?
Yes — the same ligand can activate multiple GPCR family members, leading to different cellular responses.
168
What determines the binding site location on a GPCR?
Large ligands bind to large extracellular domains.
Small ligands usually bind in a pocket within the membrane, formed by amino acids from multiple transmembrane segments.
169
What type of GTP-binding proteins do GPCRs activate?
Trimeric G-proteins, composed of α (alpha), β (beta), and γ (gamma) subunits.
170
What is the function of the α-subunit in a G-protein?
The α-subunit binds GDP/GTP and has GTPase activity, which allows it to turn signals on or off.
171
What happens to the G-protein upon GPCR activation?
The G-protein exchanges GDP for GTP on the α-subunit → α dissociates from βγ → both can interact with different effectors.
172
What makes GPCRs so versatile in signaling?
They can activate different trimeric G-proteins.
They interact with diverse downstream effectors (e.g., enzymes, ion channels).
One ligand can activate multiple GPCR types.
173
How do GPCRs amplify a signal?
A single ligand-bound GPCR can activate many G-proteins, leading to amplification of the signal inside the cell.
174
What makes GPCRs a major target for drug development?
They regulate numerous physiological processes, and ~50% of all drugs target GPCRs or their downstream pathways.
175
What are the components of a trimeric G-protein?
G-alpha (α), G-beta (β), and G-gamma (γ).
176
What is the state of trimeric G-proteins when inactive?
All three subunits are associated together, with G-alpha bound to GDP.
177
What activates the G-alpha subunit?
Exchange of GDP for GTP (triggered by GPCR activation) turns G-alpha "on".
178
What happens to the G-protein when G-alpha is activated?
G-alpha separates from the G-beta/gamma complex; both parts can activate downstream effectors.
179
Which subunits are membrane-anchored and how?
G-alpha and G-gamma are anchored to the membrane via covalently attached lipid tails.
180
What does the G-alpha subunit contain?
A GTPase domain that hydrolyzes GTP to GDP, switching the protein off.
181
Do G-beta and G-gamma ever separate from each other?
No — they remain tightly associated and act as a single functional unit.
182
What happens after GTP is hydrolyzed on G-alpha?
G-alpha rebinds GDP and reassociates with G-beta/gamma, returning the G-protein to its inactive state.
183
What happens when a GPCR binds its ligand?
When a GPCR binds its ligand, it undergoes a conformational change and activates the G-protein complex (α/β/γ) by replacing GDP with GTP on the G-alpha subunit.
184
What does the binding of GTP cause in a GPCR signaling pathway?
Binding of GTP causes a conformational change in the G-protein, which leads to the release of G-beta/gamma subunits from the G-alpha subunit, activating downstream targets.
185
What happens after the G-alpha subunit is activated?
The G-alpha subunit activates downstream targets like enzymes or ion channels, and the GPCR can activate another G-protein.
186
What causes the inactivation of the G-protein complex?
The hydrolysis of GTP to GDP on the G-alpha subunit causes the G-protein to return to its inactive state by re-associating the α/β/γ subunits.
187
How does the activation of a GPCR influence the number of G-proteins activated?
When activated, a single GPCR can trigger the activation of several G-proteins because activated G-proteins dissociate from the receptor, leaving the binding site available for further activation.
188
How does the duration of ligand binding affect GPCR signaling?
The longer the GPCR is bound to its ligand, the more G-proteins it can activate, amplifying the effect of the signaling molecule.
189
What does cAMP activate in the GPCR signaling pathway?
cAMP activates Protein Kinase A (PKA), which then activates proteins for rapid responses or transcription factors for slower gene responses.
190
What is the role of Adenylyl Cyclase in GPCR signaling?
Adenylyl cyclase is activated by the G-alpha subunit and converts ATP into cAMP, which then activates PKA.
191
What is the role of Phospholipase C (PLC) in GPCR signaling?
PLC is activated by the G-beta/gamma subunit and cleaves PIP2 into two second messengers: DAG and IP3.
192
How does IP3 affect the cell in GPCR signaling?
IP3 binds to a ligand-gated ion channel in the endoplasmic reticulum, causing the release of Ca2+, a second messenger.
193
How does DAG activate Protein Kinase C (PKC)?
DAG acts as a docking site for PKC, and the release of Ca2+ from IP3 is necessary for PKC activation.
194
What happens after PKC is activated?
Once activated, PKC phosphorylates specific targets within the cell to generate a cellular response.
195
What activates Phospholipase C (PLC) in GPCR signaling?
PLC is activated by the G-beta/gamma protein complex in response to activation of a specific GPCR.
196
What are the products of PLC cleavage of PIP2?
PLC cleaves PIP2 (phosphatidyl inositol phosphate) to produce two second messengers: DAG (diacylglycerol) and IP3 (inositol 1,4,5-triphosphate).
197
How does DAG contribute to GPCR signaling?
DAG diffuses laterally through the membrane and serves as a docking site for Protein Kinase C (PKC).
198
How does IP3 contribute to GPCR signaling?
IP3 travels to the endoplasmic reticulum and binds to a ligand-gated ion channel, causing the release of Ca2+, another second messenger.
199
What is required for PKC activation?
PKC activation requires both the docking site provided by DAG and the calcium (Ca2+) released by IP3.
200
What is the role of activated PKC in the cell?
Once activated, PKC phosphorylates specific targets, leading to cellular changes and a response to the signal.
201
What are second messengers in cell signaling?
second messengers, such as DAG, IP3, Ca2+, and cAMP, are small molecules that propagate a signal after it is initiated by a receptor binding event.
202
How does the cell restore intracellular Ca2+ to resting levels?
The cell uses specific mechanisms (such as pumps and channels) to restore intracellular Ca2+ to resting levels after signaling.
203
What are the mechanisms to deactivate signaling cascades?
Deactivation can involve:
Receptor destruction in the lysosome (permanent).
Receptor sequestration in endosomes (reversible).
Receptor inactivation by inhibitory proteins (reversible).
Inhibition of downstream signaling proteins (reversible).
204
How does negative feedback play a role in signaling cascade deactivation?
Negative feedback is used to deactivate signaling cascades by producing products that help shut down the signaling pathway.
205
What is receptor downregulation?
Downregulation involves both the receptor and signaling molecule being sent to the lysosome for destruction, thus shutting down the pathway permanently.
206
What is receptor sequestration?
Receptor sequestration involves bringing the receptor into an internal compartment (like an endosome) where it can’t interact with the signal, though it may later be recycled.
207
How does receptor inactivation occur in GPCR signaling?
Receptor inactivation occurs through the binding of an inhibitory protein, preventing the signal from being relayed.
208
How does phosphatase activity affect signaling pathways?
A phosphatase can dephosphorylate receptor tyrosine kinases (RTKs), turning off the signaling pathway and providing reversible deactivation.
209
How does a cell's response to signaling depend on its receptors?
The cell’s response depends on the types of receptors it possesses, as well as the intracellular machinery that integrates and interprets the signals.
210
