Week 7 + Module 6 Flashcards
(97 cards)
1
Q
What is slime mold
A
- eukaryotic
- transitions from a collection of unicellular amoebae to a multicellular slug, and then a fruiting body
slug: amoebas work together to form a multicellular slug which migrates towards heat, light and humidity (searches for potential food)
2
Q
what is the signal for aggregation in slime mold?
what type of response is this?
when does this aggregation occur?
what does it form?
A
cAMP
chemo-tactic
occurs in low-resource environments (starvation)
forms a slug
3
Q
what is the trans-membrane receptor for cAMP in slime mold?
A
GPCR
4
Q
what would cause cells to be unable to move towards the cAMP signal in slime mold?
A
mutation in the gene for the clathrin heavy chain
5
Q
what is the signal produced by bacteria when it enters the human body?
A
tripeptide called fMLP
(formylated Methionine-leucine-phenylalanine = produced by bacteria)
6
Q
what is the WBC response to the fMLP bacteria signal?
A
- Neutrophils have a cell-surface receptor which specifically recognizes fMLP (G-protein coupled receptor)
- Neutrophil is able to capture and engulf the bacteria through endocytosis
7
Q
transmitting information from one cell to another that induces a change in behaviour
what’s this known as
A
cell-cell signaling
involves both a response and a signal
known as the signal transduction pathway (STP) = collection of steps
8
Q
rule for specificity of signal-receptor interactions
A
A receptor will only bind to one natural ligand or closely-related molecules
one signal causes different responses in different cells
9
Q
what are examples of fast and slow cellular responses?
A
fast: changes in enzyme activation
When receptors are activated, the enzyme is activated through modifications, quickly responds to the signal by changing the protein activity already present
slow: changes in gene transcription
When the receptor is activated, the receptor itself goes into the nucleus where it directly or indirectly acts as a transcriptional activator producing mRNAs
10
Q
measuring signals of receptor affinity (graphically)
A
Vmax = 1.0 = all receptors full
Kd (dissociation constant) is the conc. of ligand required to have ½ of maximal binding and represents receptor-signal affinity
11
Q
in endocrine signalling, where are secreted signals released into?
A
the circulatory system
12
Q
what is signal for endocrine signalling?
A
hormone
13
Q
what is the target for endocrine signalling?
A
distal - target cell and signaling cell are far away from one another
14
Q
in paracrine signalling, where are secreted signals released into?
A
extracellular space
can diffuse to neighbouring cells
15
Q
what is the signal for paracrine signalling?
A
growth factors, neurotransmitters
16
Q
Para vs. endocrine signalling - which is near vs. far
A
Para = must be near
Endo = can be far
17
Q
what is the target for paracrine signalling?
A
proximal - target cell and signaling cell are close to one another
18
Q
in integral membrane proteins, where are the signalling molecules?
A
membrane bound
19
Q
in integral membrane proteins, what are the target molecules?
A
neighbours
20
Q
in plasmodesmata in plants where are the signalling molecules?
A
cytosolic
21
Q
in plasmodesmata in plants, what are the target molecules?
A
neighbours
22
Q
what are examples of signalling that requires cell contact?
A
integral membrane proteins, plasmodesmata in plants, gap junction in animals
23
Q
junctions bw two neighbouring cells that span the cell membrane and cell wall
A
plasmodesmata - in plants
24
Q
channels connecting the cytoplasm of neighbouring cells that allow the fast diffusion of small molecules from one cell to another
A
gap junctions - in animals
25
process in which a cell communicates with itself: signaling cell and the target cell are the same
autocrine signaling
26
what are the three classes of cell-surface receptors?
G-protein coupled receptors, cytokine receptors, receptor tyrosine kinases
27
this cell surface receptor controls the production of red blood cells and phosphorylation of effector protein
cytokine receptors of the JAK/STAT pathway
28
this cell surface receptor is linked to phosphorylation cascade through a small G-protein called Ras to regulate gene expression
receptor tyrosine kinases
29
this cell surface receptor activates an effector protein inside the cell to produce a secondary messenger, cAMP, that ultimately regulates cell metabolism
G-protein coupled receptors
30
Erythrocyte production + digestion
~2 million new erythrocytes (RBCs) are produced/second in the adult human body
Afterwards, are digested and recycled by phagocytic WBCs (macrophages)
31
When are erythrocytes replaced
- when mitotically-proliferating pluripotent stem/progenitor cells stop dividing and differentiate
32
what is Epo
Signal for maturation of erythrocytes = signaling cytokine protein erythropoietin
33
what regulates the expression of Epo?
oxygen-binding transcription factor in kidney cells
34
what kind of receptor is the Epo Receptor?
cytokine receptor
35
what is the cellular response to Epo?
transcription of STAT target genes, inhibition of apoptosis
36
Describe the structure and activation of the Epo receptor and the JAK-STAT pathway
The Epo receptor has three functional domains: an extracellular domain for Epo binding, a transmembrane domain, and a cytosolic domain associated with JAK kinase.
Epo binding causes receptor dimerization, bringing two JAK kinases into proximity. This proximity enables JAK kinases to phosphorylate each other (autophosphorylation), activating the receptor and creating docking sites for STAT transcription factors.
Activated JAK kinases phosphorylate STAT proteins, which then dimerize and translocate to the nucleus, activating the transcription of target genes involved in erythropoiesis.
37
protein-protein interaction domain that is essential to the function of the cytokine signaling pathway
SH2
The SH2 domain is a protein-protein interaction domain crucial for cytokine signaling. It allows proteins to bind specifically to phosphorylated tyrosine residues on target substrates. This binding can relocate proteins, such as STAT translocation to the nucleus. The SH2 domain itself does not change; its binding is regulated by the phosphorylation state of its target tyrosine residue.
38
what does PDZ bind to?
- proline rich domains
- hydrophobic residues at the C-terminus
- peptides containing phosphorylated tyrosine
hydrophobic residues at the C-terminus
39
what do SH3 and WW domains bind to?
- proline rich domains
- hydrophobic residues at the C-terminus
- peptides containing phosphorylated tyrosine
proline-rich domains
40
which of these are reversible?
- PDZ
- SH3
- WW
- SH2
- PTB
- 14-3-3
SH2, PTB, 14-3-3
41
what do SH2, PTB, and 14-3-3 domains bind to?
- proline rich domains
- hydrophobic residues at the C-terminus
- peptides containing phosphorylated tyrosine
peptides containing phosphorylated tyrosine
42
Erythrogenesis
Process of differentiation of erythroid progenitor cells into mature RBCs
RBC production
43
what transcription factor is necessary for the differentiation of mature RBCs?
STAT5
44
What is Bcl-xL and what does it do
Codes for the Bcl-XL protein which is an inhibitor of apoptosis (allows differentiation into RBCs)
45
Locations of RBC formation
Bone Marrow
- Most common
Liver
- Evident during development when all RBCs are formed in the fetal liver
46
Issue with overactivation of the cytokine pathway
- Leads to elevated haematocrit/RBC count
- Leads to an increase in the viscosity of blood, leading to blockage of narrow capillaries of the circulatory system
- Results in stroke of heart attack
- Does also allow people to carry oxygen
47
Explain the mechanisms involved in turning off the cytokine/JAK-STAT pathway
short-term regulation
Short-term inactivation by SHP1 phosphatase: SHP1 dephosphorylates JAK kinase, turning off the pathway. This dephosphorylation is reversible, allowing for quick reactivation
48
Explain the mechanisms involved in turning off the cytokine/JAK-STAT pathway
long-term regulation
(2 ways)
Long-term inactivation by SOCS protein: SOCS binds to phosphorylated docking sites, blocking STAT binding and targeting JAK kinase for degradation with E3 ubi. This mechanism is slower and requires new JAK kinase synthesis for reactivation.
or receptor is recycled (long-term inactivation)
49
this protein is expressed in response to high O2 levels in the body
SOCS protein
50
RTKs are involved in many signaling pathways that induce...
- Cell differentiation
- Cell survival or apoptosis
- Cell division and proliferation
- Changes in cell metabolism
51
what is an example of a receptor tyrosine kinase?
neural growth factor, NGF
52
which proteins link Ras to the activated RTK?
GRB2, GEF, GAP
53
MAP kinase
modulates cell behaviour by phosphorylating transcription factors and changing patterns of gene expression
54
what kind of protein is a scaffold protein?
adaptor protein
55
what is the function of adaptor proteins?
indirectly link proteins to the receptor
Carry 2+ protein interaction domains that allow proteins to act as linkers between other proteins
56
what kind of protein is GRB2 and what is it composed of?
adaptor protein; one SH2 domain and two SH3 domains
57
what does the SH2 domain recognize and what does it bind to?
phosphorylated tyrosine; binds to RTK
58
what does the SH3 domain recognize and what does it bind to?
pro-rich sequences; binds to SOS
59
promotes activation of the G-protein by dissociation of GDP and allows GTP to enter the nucleotide-binding pocket
GEF
60
Ras G-protein's activation is accelerated by this protein
GEF
Promotes dissociation of GDP and allows GTP to enter the nucleotide-binding pocket
61
Ras G-protein is DEactivated by this protein
GAP
Promotes inactivation of the G-protein by enhancing the intrinsic GTPase activity
62
Ras G-protein is INactivated by this protein
GDI
Increases affinity of nucleotide-binding pocket for GDP, keeping G-protein inactive
63
What happens when Ras-G protein interacts with SOS
SOS is a GEF
= increases activation
- SOS is relocated to the cell membrane through indirect association with the activated RTK receptor
- SH3 domains of GRB2 adaptor protein hold SOS close to the membrane
Interaction of SOS and Ras promotes release of GDP → GTP
- Ras is now active
64
3 Ras conformation states
1. Ras-GDP
- inactive
2. Ras-Sos
- displaces GDP = activates
3. Ras-GTP
- active
65
NF1 (Neurofibromatosis 1 gene)
GAP protein on Ras
- Enhances intrinsic GTPase activity (GTP hydrolysis)
- Inactivates Ras
- Presence of NF1 shortens the length of time that the G-protein is active
66
Ras - what is it
a family of proteins that transmit signals within cells
Active Ras transduces signal inside cell
67
Mutations in Ras (2)
Are associated with many human cancers;
1. Mutation leads to elimination of a single glycine residue in Ras that blocks binding of GTPase accelerating protein
2. Her2 (receptor tyrosine kinase linked to hereditary forms of breast cancer)
- Wildtype Her2 is a receptor for the EGF signal but the mutant variant does not respond to the signal and is always activated
- Mutant Her2 is always dimerized and leads to uncontrolled cell division
68
Phosphorylated residues on Raf are bound by...
by the 14-3-3 adaptor protein which holds Raf in an inhibited conformation
69
What is Raf
Ras target protein
Binding of Raf to Ras leads to release of the adaptor protein which activates Raf
Raf is a serine/threonine kinase protein at the top of the kinase cascade in the RTK pathway
70
Kinase cascade
- Kinase that will phosphorylate serine and threonine AAs on target proteins
- Raf activation leads to phosphorylation of target protein MEK
- MEK phosphorylates MAP kinase at 2 residues (tyrosine and threonine), activating this protein at the end of the cascade
- MAP kinase is a serine/threonine kinase that dimerizes upon activation and is translocated to the nucleus where target transcription factors are phosphorylated and activated
71
Activation lip
Activation lip contains threonine and tyrosine residues that are targets of dual-specificity MEK kinase:
- Change in conformation of activation lip reveals ATP and substrate binding pockets
72
MAP kinase is a ____________ target of all Ras-linked RTK signaling pathways
down or upstream
downstream
73
74
Examples of signals
- physical stimulus
- chemical molecules
75
Are hydrophobic or philic signals fast
+ examples
Phobic fast bc they can go through the membrane
- steroids
- retinoids
- thyroxine
76
What does ligand biding do
- activates receptors on target cells
- depends on noncovalent forces and molecular complementarity
77
GTP-binding proteins as switches
- switch proteins affect downstream proteins (turn on or off)
GTPase proteins are switches
GEF
- activate the GTPase
GAP
- inactivates the GTPase by hydrolysing the bound GTP
78
Trimeric vs. monomeric GTPase switches
Trimeric
- bound to receptors
Monomeric
- not bound to receptors
- include RAS proteins
79
Kinases vs. phosphatases
Kinases
- 600 in humans
- add phos to specific amino acids
(ser, threo, tyr)
Phosphatases
- 100 in humans
- remove phos groups from residues on target proteins
80
Ligands as messengers
first messengers which lead to a change in the concentration of low-molecular-weight second messengers
81
Second messengers + examples
- bind to other proteins and modify their activity
ex. calcium, cAMP, cGMP, DAG, IP3
82
What allows for signal amplification
signal transduction
83
GPCRs
- made of 7 transmembrane alpha helices
- 4 extracellular, 4 intracellular
- linked to small, trimeric G-proteins
- interact with G-proteins once a ligand is bound
84
GPCR activity regulation
when regulated, desensitized
- agonist binding to GPCR
- persistent stimulation
- GPCRS phos by GPCR kinases
- associated with arrestins
- arrestins interact with clathrin and clathrin adaptor AP2
- GPCRs internalised into endosomes and degraded in lysosomes or dephos and recycles
85
Water balance regulated at the _______ through _______
nephron
osmoregulation
86
Kidney descending and ascending osmoregulation
Descending
- water reabsorbed
- primary urine volume decreases
- pu becomes more concentrated
Ascending
- impermeable to water
- pu becomes more dilute
- ions reabsorbed
Active transport of NaCl
passive for others
87
Antidiuretic hormone regulating homeostasis
ADH hormone regulates blood osmolarity
- collecting duct increases water permeability
- counteracts low blood pressure and high plasma osmolarity
- pituitary tells hypothalamus to get water from urine when thirsty
88
What receptors and channels are needed for water permeability of principal cells of the collecting duct
Basolateral ADH receptor
Luminal aquaporin 2
89
Aquaporins
- exclusively permeable to water
- these protein channels allow water to move across the cell through osmosis
- depends on the concentration gradient
phile interior
90
Different aquaporin locations (AQP)
AQP 3 and 4
- basolateral (non-lumen) membrane
AQP 2
- cycle to the membrane of the collecting duct lining the lumen
91
How does ADH increase water permeability
- activates PKA
- phosphorylates AQP receptor and increases vesicle fusion
- reduce rate of endocytosis (receptor recycling)
AQP receptors remain at luminal surface
- increase water permeability
92
ADH receptors as GPCRs
- on basolateral side of the distal collecting duct
- allows Gas subunit to activate adenylyl cyclase
- synthesizes cAMP from ATP
- activates PKA
- helps AQP2 into luminal membrane
93
Congenital nephrogenic diabetes insipidus
- x-linked
- recessive
- mutations in the ADH receptors
- excessive thirst, large amounts of hypotonic (watery) urine
losing lots of water
- life-threatening dehydration, fatigue, seizures
- electrolyte imbalance and enlarged bladder
= nephron malfunction
94
4 classifications of ER defects
1
- loss of transcription
2
- loss of translation
- retention in ER
3
- retention in the golgi
4
- altered intracellular trafficking/insertion into the membrane
95
Cause of neph dia insipidus
inactivating mutations
- impair receptor function
- class II
- ADH receptors trapped in the ER
- loss of ADH signal so no AQP 2 expression or transport
96
How many known ADH receptor genes mutations cause XNDI
result of mutations
221
- no ADH receptors in basolateral
- no AQP channels in luminal
97
Therapies to target class 2 ADH receptor deficits
Pharmacological/molecular chaperones:
- assist in protein folding
- interact through targets with non-covalent interactions
- stabilize proteins = prevent aggregation
ex. HEK rescue by +SR121463A...
promotes proper folding
