M&R Session 6 Flashcards
0
Q
How can signalling by secreted molecules be subclassified?
A
Paracrine
Endocrine
Synaptic
1
Q
How can intracellular signalling occur?
A
Secretion of signalling molecules
Where adhesion proteins in adjacent cells are in contact
2
Q
What is paracrine signalling?
A
Signal molecules act on adjacent cells
3
Q
What is endocrine signalling?
A
Signal molecules enter the bloodstream and act on distal tissues
4
Q
What is synoptic signalling?
A
Use of neurotransmitter as a signal molecule
5
Q
How do hydrophilic signalling molecules work?
A
Bind to cell surface receptors
6
Q
How do hydrophobic signalling molecules work?
A
Transported by carrier protein and bind to intracellular receptors in cytoplasm or nucleus
7
Q
What is a receptor?
A
A molecule that recognises specifically a second molecule or family of molecules and in response brings about regulation of a cellular process
8
Q
Describe an unbound receptor.
A
Functionally silent
9
Q
What is a ligand?
A
A molecule that binds specifically to a receptor site
10
Q
What is an antagonist?
A
A ligand which binds with the receptor site but does not cause activation
11
Q
Does an antagonist switch off a receptor?
A
No. It prevent agonist binding therefore prevents switch on
12
Q
What is an agonist?
A
A ligand which binds and causes activation of a receptor
13
Q
What are the roles of receptors in cellular physiology?
A
Cell adhesion Signalling by hormones/local chemical mediators Neurotransmission Modulation of immune response Release of intracellular calcium stores Control of gene expression Cellular delivery Sorting if intracellular proteins
14
Q
How does the binding affinity at receptor sites compare to at enzyme sites?
A
Generally much higher
15
Q
What accounts for the difference in affinity b/w receptor and enzyme binding sites?
A
Ligands generally have to travel much further than substrates and allosteric regulators for enzymes therefore are more diluted
16
Q
What is KD?
A
The concentration of ligand required to half fill all available receptors
17
Q
What are they comparative ranges of affinity for receptor and enzyme binding sites?
A
Receptor = 10^-9 M to 10^-6 M Enzyme = 10^-6 M to 10^-3 M
18
Q
How are receptors classified?
A
Specific agonist
Affinity to a series of antagonists
19
Q
How are ACh receptors classified?
A
ACh
Nicotinic/muscarinic
Muscarinic into M1-M5 determined by the antagonists for which they have the highest affinity for
20
Q
Give the antagonists which the receptors M1-M3 have the highest affinity for respectively.
A
M1 = Pirenzipine M2 = Gallomine M3 = Hexahydrosiladiphenol
21
Q
How does an acceptor differ to a receptor?
A
An acceptor operates in the absence of ligand and ligand binding alone produces no response
22
Q
Give two examples of acceptor molecules, explaining why they are not receptors.
A
Dihydrofolate reductase - functions in absence of methotrexate
Sodium channel - modulated by binding of other chemicals and functions w/out anaesthetic
23
Q
What are membrane-bound receptors w/integral ion channels also called?
A
Classical ligand-gated ion channels
24
Describe the structure of nAChR.
5 subunits put -ve residues at mouth of channel
25
Give 5 examples of membrane-bound receptors w/integral ion channels.
```
nAChR
GABA receptor
Glycine receptor
Glutamate receptor
IP3 receptor
```
26
What ions do nAChR permit the passage of?
Sodium
Potassium
Calcium
27
What is the function of gamma amino butyric acid receptors?
Gated chloride channels which allow membrane hyperpolarisation
28
What ion movement do glycine receptors control?
Chloride
29
Give examples of glutamate receptors and state what ionic movement they control.
NMDA
Kainate
AMPA
All allow gated calcium entry
30
What does inositol 1,4,5-triphosphate allow?
Gated released of calcium from the ER
31
Give three examples of non-classical ligand-gated ion channels.
ATP-sensitive potassium channel
Purinoceptor
Ryanodine receptor
32
Describe the structure of ATP-sensitive potassium channels.
A channel pore with an ATP molecule on the intracellular side between 2 transmembrane domains
33
How does the structure of a purinoceptor relate to that of an ATP-sensitive potassium channel?
The same except for the shape of the channel pore and the location of the ATP molecule on the extracellular side
34
Describe the structure of a ryanodine receptor.
Four transmembrane domains with calcium and ryanodine linked to the first domain
35
Give two examples of membrane-bound receptors w/integral enzyme activity.
Atrial natriuretic peptide receptor
| Dimeric growth factor receptor
36
What are ANP receptors directly linked to?
Guanylyl cyclase (GTP --> cGMP)
37
What are dimeric growth factor receptors directly linked to?
Tyrosine kinase
38
Describe the mechanism of dimeric growth factor receptors.
Allow phosphorylation of tyrosine for growth
39
Give some examples of the resultant molecules from activation of dimeric growth factor receptors.
Insulin
Epidermal growth factor
Platelet-derived growth factor
40
What is autophosphorylation?
Phosphorylation of the chain in the opposite subunit of a dimer - allows cross communication
41
How does autophosphorylation facilitate the function of a tyrosine kinase-linked receptor?
The multiple phosphorylated a.a. residues give a specific site for binding which is recognised by transducing proteins which are allosterically activated/phosphorylated to regulated an intracellular event
42
How are insulin receptors synthesised?
Alpha and beta chains are made together and cleaved extracellularly, held together in the membrane by sulphide bridges
43
Describe the structure of insulin receptors in the plasma membrane.
Two tyrosine kinase domains intracellularly
Two transmembrane domains joined by a disulphide link (beta chains)
Two insulin binding domains linked to the two transmembrane domains by disulphide links (alpha chains) extracellularly
44
Give three examples of membrane-bound receptors that signal through transducing proteins.
Coupled through GTP-binding regulatory proteins to enzymes/channels
Beta-adrenoreceptors activate the enzyme adenylyl cyclase via Gs
M2 stimulates potassium channel opening by Gi
45
Where are binding domains found in GPCRs?
W/in the plane of the bilayer
46
How many transmembrane receptors are there in membrane bound receptors that single through transducing proteins?
Seven
47
Where are both beta-adrenoreceptors and M2 receptors found?
In the heart
48
Describe the function of activating stimulatory/inhibitory receptors in receptors that use transducing proteins.
Receptor binding causes dissociation of GTP from alpha-s/i which acts in the target enzyme to stimulate/inhibit it
49
Describe the mechanism of action of beta-adrenoreceptors.
Adrenaline binds--> G-protein subunit dissociation (alpha and beta move away)--> Gs-alpha binds to target enzyme adenylyl cyclase whilst it is combined with a new molecule of GTP --> cAMP produced
50
What changes between intracellular receptors?
Their primary structure
51
What do all hydrophobic signals use?
Similarity of sequence of intracellular receptors
52
Describe the mechanism of intracellular receptor activation.
Binding of hormone --> huge conformational change --> inhibitory protein complex removed --> DNA binding site exposed
53
What is the DNA binding site of an intracellular receptor also known as?
Zinc fingers
54
What are intracellular receptors silent at rest?
The DNA site is blocked
55
Describe the mechanism of amplification.
Single, v. low concentration signal molecule binds in one receptor --> small number of GPCR activated --> cAMP --> PKA --> emzyme --> products
56
What is the magnitude of amplication by receptors?
x10^9
57
Compare the activation and inhibition of receptors in hepatocytes.
Insulin stimulates glycogenesis
| Glucagon stimulates glycogenolysis
58
How is heart rate increased in cardiac pacemaker cells?
Noradrenaline binds to beta-1 adrenoreceptors
59
How is heart rate decreased in cardiac pacemaker cells?
ACh binds to M2 muscarinic receptors
60
How is the plasma membrane trafficked to its final position?
From the ER to the CSM via the exocytic secretory pathway
61
What prevents the CSM being excessively ruffled?
Endocytosis of the membrane
62
What is the pathway of vesicular transport of membrane?
Donor organelle --> membrane vesicle --> trafficked to destination --> fuse w/recipient organelle
63
What is the function of pinocytosis?
Permits uptake of extracellular so lutes
64
How does pinocytosis take place?
Invagination of the CSM to form a vesicle
65
What is the function of phagocytosis?
Internalisation of particulate matter
66
What is the mechanism of phagocytosis?
Receptors sequentially bind to 'zip up' around engulfed material
67
Describe endocytosis.
Selective internalisation of molecules into cell by binding to specific cell surface receptors
68
What is cholesterol uptake an example of?
Receptor-mediated-endocytosis
69
Describe the structure of LDLs
Core of esterified cholesterol
Contain apoprotein B
Core covered by a phospholipid and cholesterol monolayer
70
What do triskelions comprise of?
3 clathrin heavy chains
3 clathrin light chains
Always arranged in the same way
71
What allows the coat structure to form vesicles instead of tubes and sheets?
The hexagon and pentagon structure
72
Describe the mechanism of clathrin coating.
Clathrin coated pits form spontaneously --> protein coats prevent vesicle binding so must be removed --> uncoated by an ATP-dependent uncoating protein
73
How do clathrin coated pits form spontaneously?
Association of more and more triskelions on cell face
74
What happens to the clathrin triskelions removed by the uncoating protein?
Recycled back to newly forming clathrin coated pits
75
What two mutations can occur which affect LDL receptor in hypercholesteroleamia?
Non functional receptor
| Receptor binding normal but no internalisation
76
What happens when there is no internalisation of LDL receptors?
LDL receptors are over the whole cell surface, not localised into pits
Deletion of C-terminal cytoplasmic domain prevents interaction w/clathrin coat
77
What is the fate of the ligand and receptor in cholesterol uptake?
Ligand degraded
| Receptor recycled
78
What is CURL?
Compartment of Uncoupling of Receptor and Ligand
79
What is the affect of the low pH in the endosome?
It decreases the affinity of the receptor for LDL
80
What molecule allows uptake of ferric ions?
Transferrin
81
Describe the uptake of ferric ions.
Ferrotransferrin binds to transferrin receptor in coated pits --> coated vesicles --> pH in vesicle decreases due to hydrogen-ATPase --> ferric ions released from CURL --> apotransferrin released by CURL in pH 5 vesicle --> neutral pH at cell surface causes dissociation of apotransferrin from receptor
82
Why is it useful for the ligand to be recycled in ferric ion uptake?
It is a large molecule so you don't want to use lots of energy having to make it
83
What is the fate of the ligand and receptor in ferric ion uptake?
Ligand recycled
| Receptor recycled
84
What is the fate of the ligand and receptor in the endocytosis of insulin?
Ligand degraded
| Receptor degraded
85
What happens if insulin is high for a long time?
Receptors are removed to prevent overreaction but then it takes a few hours to synthesise replacements
86
How does chronic hyperglycaemia lead to T2DM?
Vicious cycle arises as the body works v.hard to make enough receptors --> beta-cells give up --> T2DM
87
What can cause insulin deficiency?
Genetic factors
| Glucose toxicity
88
What can cause insulin resistance?
Genetics
| Environment
89
What is the fate of the ligand and receptor in endocytosis of immunoglobulin?
Ligand transported
| Receptor transported
90
Describe the endocytosis of immunoglobulin.
Binds to receptor in coated pits --> coated vesicle --> uncoated vesicle --> endosome --> transfer vesicle --> bile canaliculi
91
What is the endocytosis of immunoglobulin an example of?
Transcytosis of a large molecule across a cell
92
How is IgA released?
Proteolytic cleavage of the receptor --> see small part of the ligand w/receptor
93
How do membrane-enveloped viruses take advantage of receptor mediated endocytosis?
Fortuitous association w/cell receptors
Clathrin-coated pits
Unfolding hydrophobic domains in membrane fusion proteins in response to the acidic pH of the endosome
Insert membrane fusion proteins into endosome membrane --> membrane fusion and release of genomic RNA into cytosol
Use host machinery to replicate RNA and capsid proteins
94
How do cholera and diphtheria toxins act?
Bind to GM1 ganglioside which is incorporated into the vesicle
95
Do cholera and diphtheria bind to a receptor?
No
96
Name three coat proteins.
Clathrin
COPI
COPII
97
What are COP?
Family of coat proteins for vesicles from different organelles
98
What shapes are COP made up of?
Squares and triangles
99
Where is COPI from?
The ER
100
Where is COPII from?
The Golgi apparatus
