Cell signalling and pharmacology Flashcards
(98 cards)
1
Q
What controls the breeding behaviour of prairie voiles in males and females?
A
females - oxytocin
males - vasopressin
2
Q
Describe the mechanism of intercellular signalling
A
- signalling cell produces a signalling molecule
- signalling molecule detected by receptor on target cell
- receptor is specific to the signalling molecule
3
Q
List the two broad classes of extracellular signalling molecules
A
large and/or hydrophilic –> bind to cell surface receptors
small and/or hydrophilic –> enter cell and bind to intracellular receptors
4
Q
What is meant by paracrine signalling?
A
the released signal affects cells in close proximity (local mediators) and there is limited travel availability
examples include: growth factors, histamine, nitric oxide
5
Q
What is meant by autocrine signalling?
A
the sender and target cell are the same
some examples include: molecules regulating development and some growth factors
6
Q
What is meant by endocrine signalling?
A
usually the signal acts on distant cell and involves hormones
examples include: insulin, glucagon, testosterone, oestrogen and adrenaline
7
Q
What is meant by juxtacrine signalling?
A
the signalling cell is in direct contact with target cell
8
Q
What is signal transduction?
A
- linked with cell surface receptors and not intracellular receptors
- begins when receptors on the cell surface receive the signal and convert/relay the message to a molecule inside the cell
- the signal is then transduced along many intracellular molecules
9
Q
How can the same signal molecule induce different responses in different target cells?
A
- via variants or isoforms of the same receptor
- similar receptors use different intracellular signal transduction pathways
10
Q
How are messages relayed in a signal transduction pathway?
A
mainly by changes in the state of proteins which is detected by the next molecule in the sequence, which in turn becomes altered
11
Q
How are protein alterations induced?
A
- molecules binding with each other
- addition/removal of a phosphate
- molecule binds to a phosphate on another molecule
12
Q
What is the point of a signal transduction pathway?
A
- amplify the original signal
- integrate and distribute signals coming from other signal transduction pathways
13
Q
How are scaffold proteins useful?
A
they allow for some signalling components to be activated more efficiently
14
Q
List the types of molecules involved in signal transduction pathways
A
- proteins
- lipids
- small chemical mediators
- ions
- gases
15
Q
Describe how intracellular proteins act as molecular switches
A
- toggle between inactive and active states
comprised of two broad classes which are activated/deactivated by:
- binding to guanine nucleotides - GTP and GDP
- phosphorylation
16
Q
How are G proteins regulated?
A
- inactive when bound to GDP
- active when bound to GTP
intrinsic GTPase activity
- hydrolysis of GTP to GDP switches off protein
17
Q
Describe the two forms that G proteins can exist as
A
- within a trimeric complex
- as a single monomeric pattern
18
Q
Describe the requirements for activation/inactivation of monomeric G proteins
A
- GEFs to aid in GDP/GTP exchange
- GAPs to aid in GTP hydrolysis
19
Q
List the key members of monomeric G proteins and their functions
A
Ras –> cell division and growth
Rab –> membrane transport and vesicular transport
Rac and Rho –> cytoskeleton organization, migration
20
Q
Describe how phosphorylation is undertaken by protein kinases
A
Add phosphate from ATP to specific amino acids on target protein
- tyrosine kinases (TKs)
- serine/threonine kinases (STKs)
covalent modification reversed by protein phosphatases
21
Q
List the features of protein kinases
A
- are switch proteins themselves
- often organised in sequence in a signal transduction pathway
- once activated, can in turn phosphorylate and activate the next protein kinase in the sequence
22
Q
which enzyme produces cAMP?
A
adenylyl cyclase
23
Q
Describe the structure of adenyl cyclase
A
consists of two transmembrane domains, joined by a catalytic intracellular domain
24
Q
How is cAMP degraded?
A
degraded from a cyclic nucleotide to a 5’monophosphate (AMP) by a cAMP phosphodiesterase
25
How are responses to cAMP mediated
via cAMP-dependent protein kinase A
- inactive PKA consists of two regulatory (R) subunits and two catalytic (C) kinase subunits
- cAMP binds to the R subunits --> molecule dissociates to produce 2 monomeric kinase units
- monomeric kinase units are active and can bind and phosphorylate target proteins
26
What is PIP2?
- phosphatidylinositol 4,5-bisphosphate
- cell membrane phospholipid
27
What is PIP2 comprised of?
- hydrophobic diaglycerol (DAG) lipid tail
- hydrophilic inositol sugar as head group --> inositol triphosphate (IP3)
28
Where is PIP2 found?
in inner leaflet of lipid bilayer
29
Describe how phosphorylation of PIP2 is regulated in the lipid bilayer
- phosphorylated by P13-kinase (lipid kinase) to form PIP3
- binds to PDK1
- regulatory molecule is PTEN
- PTEN dephosphorylates PIP3 back to PIP2 --> shuts down signal via PKB
30
What causes the breakdown of PIP2 in the lipid bilayer?
phospholipase C (PLC)
31
Describe the breakdown of PIP2
- activation of phospholipase C (PLC)
- cleaves PIP2 into DAG and IP£
- DAG activates protein kinase C (PKC)
- IP3 triggers release of Ca2+
32
List two ways in which the concentration of Ca2+ can increase
- influx of Ca2+ from outside cell via channel proteins in plasma membrane
- release of Ca2+ from intracellular stores --> ER, SR, mitochondria
33
How can Ca2+ concentration be reduced?
via ATPase pumps in:
- plasma membrane (pump out Ca2+)
- ER, SR and mitochondrial membrane (sequester Ca2+ back into organelle)
34
Describe the structure and function of calmodulin
- has four Ca2+ binding sites
- activated when [Ca2+] increases above 500nM
- Ca2+ bound calmodulin binds and activates target proteins
35
How can signalling events be terminated?
- eliminate extracellular signalling molecule --> enzymatic degradation
- deactivate signal transduction molecules --> dephosphorylation by phosphatases, degradation by enzymes
- remove activated receptor from cell membrane by endocytosis --> either receptor and signalling molecule separated and ligand destroyed or receptor and ligand both destroyed
36
How does a signalling molecule exert its effects?
binds to its specific receptor --> lock-and-key
37
How can the cell influence the response of the signalling molecule?
- regulating the number of receptors
- synthesising different isoforms of the receptor
38
What is an agonist
a molecule that binds and activates a receptor, inducing signalling and a biological response --> full activation/partial activation
39
What is an antagonist?
a molecule that binds to a receptor but does not induce signalling and a biological response
40
List the types of cell surface receptors
- ion channel-linked receptor --> ionotropic receptor
- G protein coupled receptor --> metabotropic receptor
- enzyme-linked receptor --> intrinsic enzyme activity, recruit enzyme from cytoplasm
41
Describe the mechanisms of ion channel-linked receptors
- act as gates
- ligand binding causes receptor to change shape and open gate
- allows ion flow passively through channel
42
How can ion channel-linked receptors be pharmacologically modified?
- channel blockers
- channel modulators --> bind to channel and enhance or inhibit opening
43
What are GPCRs?
- largest family of cell surface receptors
- mediate wide array of physiological processes --> odorant detection
44
Describe the structure of GPCRs
- extracellular ligand binding region
- seven alpha helices that span the membrane
- intracellular portion interacts with a trimeric G protein
45
Describe the features of a trimeric G protein
- 3 subunits --> a,B,y
- Ga unit binds GDP/GTP and has the GTPase activity
46
Describe signal relay via the GPCR
- binding of ligand alters the conformation of the receptor
- G apha unit binds to receptor
- Binding of G alpha protein allows release of GDP and its exchanged for GTP
- alpha subunit is active and dissociates from the B and Y units
- Both active G alpha subunit and By complex can now interact with effectors molecules
- GTP bound activated G alpha unit binds to an effector molecule altering its activity
47
How is the G protein switched off?
- G alpha subunit hydrolyses the GTP to GDP --> can use RGS protein to aid hydrolysis
- G alpha dissociates from effector molecules
- alpha subunit returns to original GDP inactive conformation --> reassembles with BY complex to form inactive trimeric G protein
48
List the effector molecule and the effect on the effector molecule of Gas
- adenylyl cyclase
- stimulation --> increase in cAMP
49
List the effector molecule and the effect on the effector molecule of Gai
- adenylyl cyclase
- inhibition --> decrease in cAMP
50
List the effector molecule and the effect on the effector molecule of Gaq
- phospholipase C
- stimulation --> increase in DAG and IP3
51
Describe how cholera can cause dysregulated G protein signalling
- cholera toxin binds to Gas and fixes it in GTP bound conformation
- over stimulation of adenylyl cyclase and cAMP production
- downstream signalling effects lead to water loss
52
What do GPCRs that are coupled to the Gaq class of G protein activate?
phospholipase C --> induce Ca2+ mediated events
53
What do receptor tryosine kinases (RTK) consist of?
- extracellular domain which binds the ligand
- transmembrane domain
- intracellular or cytoplasmic domain which contains the tyrosine kinase site --> a tyrosine kinase adds phosphate groups from ATP to only tyrosine residues on target protein
54
How are RTKs activated?
- requires dimerization of two receptor monomers
- activates the tyrosine kinase in each receptor
- kinase phosphorylates tyrosines on opposite receptor tail
- recruitment/binding of adaptor and/or effector signalling molecules directly to the phosphorylated tyrosines to initiate signalling
55
What do RTKs commonly use to relay or transduce the signal?
the monomeric G protein Ras --> activated receptor directy/indirectly binds and activates the GEF for Ras
56
Where are glucose transporters stored?
in the walls of cytoplasmic vesicles
57
How does insulin regulate glucose uptake?
- insulin induced IRS-1/PI-3 kinase/PKB signalling triggers vesicle translocation to the plasma membrane
- vesicle fuse with membrane where they take up glucose and pass it into the cell
58
How do cytokine receptors recruit Janus kinase
- cytokine receptors lack intrinsic kinase activity
- recruit soluble tyrosine kinase (JAK)
ligand binding causes:
- receptor dimerisation and JAK recruitment and activation
- JAKs phosphorylate each other and receptor
- recruitment of STAT transcription factor to phosphorylated tyrosine residues on receptor
59
Where can intracellular receptors be found?
in the nucleus or cytoplasm --> after binding ligand, cytoplasmic receptors will translocate to nucleus
60
What is the purpose of intracellular receptors
- bind lipid soluble molecules such as steroid hormones or small molecules
- exert effects by affecting gene transcription
61
What do nuclear receptors contain?
- a ligand binding domain
- a DNA binding region --> bind to response elements in the promoter region of genes
- N terminal variable region --> can be modified by other molecules
62
Describe the mediation of gene transcription by cortisol
- cortisol produced in adrenal glands in response to stress
- passes through lipid bilayer and binds to its cytoplasmic nuclear receptor
- ligand-bound receptor translocates to nucleus
- binds to regulatory response elements in target gene to drive gene transcription
63
Describe the mediation of gene transcription by oestradiol
- oestradiol is synthesized from testosterone by aromatase
- oestradiol is hydrophobic and passes through the nuclear membrane
- within the nucleus, oestradiol binds to oetrogen receptors which dimerise, associate with co-activators and form a complex which acts a transcription factor
- transcription factor activates estrogen-response elements, altering the trancription of target genes
64
What are the methods of transport: into vascular systems, into cells and from cell to cell
- via active transport via transport proteins
- passive
- via plasmodesmata
65
What are plasmodesmata?
- comprised of cytoplasmic channels linking adjacent cells
- 30-60nm in diameter
- allows passage of small molecules and macromolecules
- aids in electrical signalling between plant cells
66
Describe the process of electrical signalling in venus flytraps
- stimulation of sensory trigger hairs activates mechano-sensitive ion channels
- lead to depolarization of membrane and generation of an AP
- changes turgor pressure in hinge cells, causing closure of leaf lobes
67
List the transduction components present in plants
- membrane enzyme-linked receptors and intracellular receptors, with and without kinase activity
- use mainly serine/threonine kinases
- intracellular signalling molecules
68
Describe how signal transduction can alter gene expression
- by positive gene activation
- inactivation of transcriptional repressor proteins
69
What is the natural auxin in plants?
indoleacetic acid (IAA)
70
Where are auxins produced?
in the seed embryo, meristems of apical buds and young leaves
71
What are the functions of auxins?
- stem elongation
- root growth
- branching
- fruit development
- apical dominance
72
How are auxins transported from one cell to the next
active transport --> long distance and local acting
73
Describe the phototropic response of shoots
- mediated by the blue-light photoreceptor phototropin
- signalling causes redistribution of auxin to shaded side
- induces cell elongation on shaded side
- shoot bends towards light
74
Describe how auxin inactivates repressor protein to affect gene transcription
- auxin binds to its nuclear receptors --> ubiquitin ligases
- binding promotes ubiquitinylation and degradation of repressor protein
- suppression of gene transcription is releived
75
What are the functions of ethylene?
- fruit ripening and leaf abscission --> can pass through cell walls or diffuse through air
76
Where are ethylene receptors found?
in the membrane of the endoplasmic reticulum and golgi
77
Describe the ethylene response
- in the absence of ethylene, the ethylene receptor is activating a kinase - promoting destruction of the transcription regulator
- deactivation of the ethylene receptor allows transcription of ethylene sensitive genes
78
List the three types of blue-light receptors
- cryptochromes
- phototropin
- zeaxanthin
(cell surface receptors)
79
What kind of receptor is phytochromes
- an intracellular photoreceptor
- red light and far-red light
80
Describe the roles of photorecepotrs in plant physiology
- cryptochromes --> influence de-etiolation (development and expansion of leaves)
- phototropins --> influences auxin redistribution
- phytochromes --> regulate photoperiodism (response of plants to period of day)
81
Describe the features of phytochromes
- exist as two subunits
- each has a light detecting pigment or chromophore
- a region that has kinase activity
- exist between two states: Pr and Pfr depending on proportion of red light/ far red light
82
How can Pfr modulate gene transcription?
- translocating to the nucleus
- directly binding to and activating a transcription factor
- indirectly phosphorylating transcription factors
83
How is apoptosis essential for animal development?
- removal of redundant structures
- embryogenesis --> sculpting of limbs
84
What are the consequences of too much and too little apoptosis?
too much --> degenerative diseases
too little --> diseases of over-proliferation (tumours)
85
List the the type of damaged cells that are removed by apoptosis
- DNA damage
- Accumulation of misfolded proteins --> linked with neurodegenerative disorders, causes ER stress and cell death
- cells infected by certain viral agents --> limits spread of infection
86
List the stages of apoptosis
- cell shrinkage
- chromatin condensation
- fragmentation of intracellular contents and membrane blebbing
- formation of apoptotic bodies --> membrane-bound portions of cytoplasm and organelles
- phagocytic ingestion of Abs and degradation
87
What family of proteases mediate apoptosis in animal cells?
caspases
88
Describe the features of caspases
- cysteine at active site
- cleaves target proteins at specific aspartic acids
- synthesised as inactive procaspase
- activated by proteolytic cleavage at own aspartic residues
89
What are the functions of intiator caspases?
- undergo autocleavage
- activates other caspases
90
What are the functions of effector caspases
- activate other effector caspases after cleavage by initiator caspase
- cleave cellular proteins
91
Describe the nuclear effects seen during apoptosis
- hallmark cleavage of chromosomal DNA
- caspase cleaves a protein that normally blocks endonuclease action
- DNA cleavage by endonucleases cuts DNA into internucleosomal units
- apoptotic cells show DNA laddering on electrophoresis
92
What is the key 'engluf-me' signal for phagocytes?
phosphotidylserine (PS)
93
Where is PS normally found?
in the inner leaflet of plasma membrane
- in apoptosis some PS molecules move to outer leaflet
- action of caspases activate scramblase (Xkr8) --> mediates PS flipping
94
What determines whether the intrinsic pathway of apoptosis is activated?
cytochrome c --> from mitochondria
95
List some pro-apoptotic molecules
BAX
BAK
^^ promote apoptosis by forming channels in outer mitochondrial membrane for release of cytochrome c
BAD
96
List some anti-apoptotic molecules
BCL-2 --> inhibits apoptosis by blocking action of BAX and BAK and preventing release of cytochrome c
BCL-XL
97
How does survival factor/growth factor suppress apoptosis?
- increasing transcription and translation of anti-apoptotic molecules
- signal transduction kinases (activated by stimulation of trophic receptors) phosphorylate and inactivate pro-apoptotic molecules
98
Describe the extrinsic pathway
- used by cells of the immune system to kill targets
- initiated by death ligands secreted by the immune cells
- activated death receptors result in caspase cascade
