Molecular Signalling Flashcards
1
Q
Essential components of intercellular communication
A
- signalling cell
- signal
- receptor
- target molecule
- response
2
Q
Forms of intercellular communication
A
- synaptic
- paracrine
- endocrine
3
Q
Types of signals mediating intercellular communication
A
- signalling molecules can be
- cell-impermeant (cant diffuse through cell - need receptors on post cell)
- cell permeant (can diffuse through post cell)
- cell-associated (signalling molecule is attached to pre cell)
4
Q
Mechanisms of target protein regulation
A
- protein targets of signalling cascades are often phosphorylated on SERINE, THREONINE, or TYROSINE residues
- by Ser/Thr kinases and Tyrosine kinases
- phosphorylation leads to changes in protein structure or ability of protein to bind other proteins (changes its function)
- dephosphorylation by protein phosphatases reverses change
5
Q
Ionotropic receptors
A
- ligand gated ion channels
- binding of ligand causes channel to open
- channel is ion selective
- diffusion of ions in/out of cytoplasm elicits change in membrane potential
- if ion channel permeable to calcium, calcium signalling initiated
6
Q
Ionotropic receptor structure
A
- 4-5 subunits grouped around a central pore
- charged amino acid residues at pore entrance form ion selectivity filter
- gate in pore center opens with ligand binding
- DESENSITIZATION: closing when ligand is bound for long time
7
Q
Metabotropic receptors
A
=GPCRs
- bind heterotrimeric G proteins
- binding of ligand = signal and activated the G protein
- G protein regulates enzymes and ion channels
8
Q
Metabotropic receptor structure
A
- common structure: 7 transmembrane receptors
- ligand binding leads to conformational change in receptor that leads to replacement of GDP for GTP in G protein
9
Q
Enzyme linked receptors
A
- have an intracellular domain that is enzymatically active
- Receptor Tyrosine Kinases
- Ser/Thr kinases
- Tyrosine and S/T phosphatases
- Guanylyl cyclases
-signalling binding to extracellular domain activates enzyme activity
10
Q
Enzyme linked receptor: RTK
A
- activation of RTC involves:
- Ligand binding
- Receptor DIMERIZES (2 halves come together with NGF dimer as ligand
- Autophosphorylation
- Binding of effectors, phosphorylation of other proteins
11
Q
Intracellular receptors
A
- activated by lipophilic signalling molecules that diffuse across PM
- binding of signalling molecule causes disinhibition of receptor (activates it) by dissociation of inhibitory protein
- cytosolic receptors translocate the receptor to the nucleus
- the activator receptors bind co-activator proteins and/or DNA to induce GENE TRANSCRIPTION
12
Q
Properties of G Proteins
A
- able to bind and hydrolyze GTP
- regulate effectors (enzymes or ion channels)
- only interact with effectors when GTP bound
- inactive in GDP bound form
13
Q
Classes of G proteins
A
- heterotrimeric:
- composed of 3 subunits (a, B, Y)
- activated by METABOTROPIC receptors
- small monomeric:
- single polypeptides
- activation by RECEPTOR TYROSINE KINASES
14
Q
Activation/Inactivation of heterotrimeric G proteins
A
- ligand binds to GPCR
- GPCR promotes exchange of GDP for GTP
- G protein a subunit dissociated from BY subunit and leaves receptor
- Both a and BY subunit can interact with effectors
- GTPase activating protein (GAP) facilitated GTP hydrolysis (turning a unit back to GDP bound)
- Subunits reassociate with GPCR
15
Q
Types and targets of heterotrimeric G proteins
A
Gs: activates adenylate cyclase
-increases cAMP production
Gi: inhibits adenylate cyclase
-decrease cAMP production
Gq: activates phospholipase C (PLC)
-increase diacyclglycreol and IP3 production
Gt (transducin): activates cGMP phosphodiesterase (PDE)
-decrease cGMP
16
Q
Activation of small monomeric G proteins
A
- Guanine nucleotide exchange factor (GEF) facilitates replacement of GDP by GTP
- activates G protein
- GTPase activating protein (GAP) facilitates hydrolysis of GTP
- inactivates protein
- GEFs can be activated by active RTKs
- GAPs can be regulated by upstream signalling
17
Q
Targets of monomeric G proteins
A
- ras: functions in cell proliferation, differentiation, survival
- effector: MAP kinase pathway
- rho: functions in actin dynamics
- effector: ROCK kinase
- rab: function sin membrane trafficking
- effector: various
18
Q
MAP kinase pathway
A
- activated RTK causes GEF to facilitate exchange of GDP for GTP bound Ras
- Ras (membrane bound) activates MAPKKK
- MAPKKK phosphorylates (activates) MAPKK
- MAPKK phosphorylates (activates) MAPK
- MAPK phosphorylates and regulates many proteins
19
Q
cAMP
A
- cAMP = cyclic adenosine monophosphate
- generated by adenylyl Cyclades (activated by Gs, inhibited by Gi)
- activates protein kinase a (PKA)
- binds and modulates conductance of cyclic nucleotide-gated ion channels
-cAMP degrades by phosphodiesterases (PDE)
20
Q
Protein kinase A
A
- is a serine/threonine kinase
- phosphorylates proteins involved in synaptic transmission, glucose, and lipid metabolism
- 2 catalytic, 2 regulatory subunits
- cAMP bind to regulatory subunits, relieving inhibition of the catalytic subunits (so they are then active)
21
Q
cGMP
A
- cGMP = cyclic guanosine monophosphate
- generated by guanylyl cyclase
- activates protein kinase G (PKG)
- binds and modulates cyclic nucleotide gated ion channels
- cGMP degraded by Gt (transducin) activated phosphodiesterases (PDE)
- cGMP important second messenger in photoreceptors
22
Q
IP3 and diacylglycerol
A
- PIP2 is a phospholipid in PM
- cleavage of PIP2 by phospholipase C (PLC) yields diacylglycerol (DAG - membrane bound 2 messenger) and inositol trisphosphate (IP3 - 2 messenger in cystol_
- multiple PLC activated by Gq proteins, tyrosine kinase, and calcium
- IP3 binds to and activates IP3 receptors (ligand gated Ca2+ channels in ER membrane)
- Ca2+ released from ER stores is 3rd messenger
- initiates Ca2+ dependent signalling
- DAG (and Ca2+) activates PKC (Ser/Thr kinase)
23
Q
Maintenance of basal cytoplasmic Ca2+ concentration
A
-Basal Ca2+ conc in cytoplasm is low (<100nm) due to:
- Extrusion by plasma membrane Ca2+ ATPase (PMCA)
- Uptake into ER by sarco/edoplasmic reticulum calcium ATPase (SERCA)
- Buffering by Ca2+ binding proteins
- Mitochondrial calcium uptake
24
Q
Sources of Ca2+ signals
A
-transient, specially restricted calcium signal through opening of:
- Voltage gated calcium channels
- ligand gated calcium channels
- IP3 receptors
- Ryanodine receptors (from ER, Ca2+ gated)
25
Q
Ca2+ effectors
A
-transient, local calcium elevations activate Ca2+ effectors:
- Ca2+ activated Calmodulin (CaM)
- Ca2+/CaM binds and modulated kinases, calcium channels…
- modulation of synaptic transmission by Ca2+/CaM dependent Kinase 11 (CaMKII)
- which is a Ser/thr kinase
26
Q
Locally restricted Calcium signalling
A
- due to efficient calcium buffering, extrusion: calcium signalling often local rather than cell-wide
- compartmentalization of calcium signals in dendritic spines
27
Q
Regulation of gene expression by signal transduction pathways
A
- synthesis of new mRNA and proteins regulated by signal transduction pathways
- slow onset (>30min), long lasting
- gene transcription requires binding of transcriptional activator proteins to DNA near promoter region of target gene
- binding of transcriptional activator allows formation of RNA polymerase complex, transcription of gene
28
Q
CREB signalling
A
- cAMP responsive CREB needs to be phosphorylated to have transcriptional activity
- phosphorylated by PKA, MAPK (from ras) and Ca2+/CaM kinase
- activated CREB stimulates transcription of specific genes
29
Q
C-fos signalling
A
- c-fos: transcriptional activator that is present in unstimulated cells at low concentration
- c-fos: is immediate early gene: stimulus by MAPK, PKA, CaMK directly elicits transcription of c-fos
- synthesized c-fos protein then stimulates transcription of other genes
- CREB activates synthesis of mRNA from c-fos gene, which is turned into a protein which works as a transcriptional activator
30
Q
Divergent signal transduction: NGF
A
- NGF = neurotrophic growth factor
- TrkA = NGF receptor (RTK receptor)
- required by sensory and sympathetic neurons for survival, differentiation, neurite outgrowth
- activation of multiple signalling pathways: PLC, ras/MAPK
31
Q
Convergent signal transduction: tyrosine hydroxylase
A
- TH catalysts first step in synthesis of catecholamine NT
- phosphorylation of TH leads to increase in enzyme activity, and increased catecholamine synthesis
- TH phosphorylation by PKA, PKC, MAPK, CaMKII: convergent signalling
