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Biomedicine Semester 1 > Cell Signalling > Flashcards

Cell Signalling Flashcards

(68 cards)

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1
Q

Describe communicaion

A

a process by which information is exchanged between individuals through a common system

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2
Q

Describe a simple signalling pathway

A

Signal: extracellular activator of the pathway

Reception: detection of signal pathways

Response: change in cellular process

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3
Q

How can you alter the activity of a signalling pathway?

A
  • changing the level of the protein

- changing the activity of a fixed amount of protein via a conformational change or a covalent modification

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4
Q

What are the different cell signalling methods from local to distant range

A

Gap junction, Contact-dependent, Paracrine, Synaptic, Endocrine

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5
Q

What is a gap junction?

A

an intracellular gap that allows small signalling molecules to pass directly from cell to cell

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6
Q

What molecules can pass through gap junctions

A

Ions: Na+, Ca+, K+

Metabolites: sugars, amino acids, nucleotides, AT, cAMP, InsP3

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7
Q

Describe contact-dependent signalling

A
  • not secreted
  • signalling molecule on surface interacts directly w receptor on recipient cell
  • important for immune signalling and during development
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8
Q

Describe paracrine signaliing

A
  • use of local mediators that act on different cell types in close proximity
  • important during inflammation and development
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9
Q

Describe autocrine signaling

A
  • it’s self signalling i.e the cell is able to bind the signal it excretes
  • other cells of the same type can bind the signal
  • encourages to grow and proliferate
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10
Q

What are the properties of a signal that binds to intracellular receptors

A

small, hydrophobic i.e steroid hormones and NO gas

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11
Q

What are the properties of a signal that binds to extracellular receptors

A

hydrophilic as they can’t cross the cell-surface receptors i.e cytokines and neurotransmitters

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12
Q

What are the 3 types of cell surface receptors

A
  • ion channel coupled receptors
  • G-protein coupled receptors
  • enzyme coupled receptors
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13
Q

What do ion channel coupled receptors do

A

they convert chemical signals to electrical signals in the nerve

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14
Q

How do ion channel coupled receptors work

A

the binding of a ligand induces a conformational change in the receptor

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15
Q

What is an example of ion channel coupled receptors

A

Nicotinic acetylcholine receptors on skeletal muscles

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16
Q

How do nicotinic receptors work

A

when ach binds to the subunits causing a conformational change allowing Ca2+ into the cell

This causes a depolarisation therefore there is contraction

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17
Q

What are nicoinic receptors an example of

A

ionotropic receptors and fast receptors

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18
Q

What causes Myasthenia Gravis

A

Auto-antibodies block nicotinic receptors causing muscle weakness

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19
Q

What are Trimeric G proteins

A

3 subunits; alpha, beta and gamma

they’re transducers linked to G-protein linked receptors

convert one signal from one form to another

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20
Q

What are monomeric G proteins

A

single subunits activated when attached to GTP

transduce signals from enzyme linked receptors

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21
Q

Describe the alpha-subunit within the trimeric G protein

A

it has intrinsic GTPase activity and binds GDP in its resting state

it conatins2 subdomains; RAS and AH

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22
Q

Describe the function of the Ras and AH domains

A

RAS: one face of the nucleotide-binding pocket

AH: clamps the nucleotide in place

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23
Q

Describe the steps leading up to the dissociation of the beta/gamma subunits and the activation of the alpha subunit

A

1- signal induces conformational change in receptor and alpha-subunit

2- alpha-subunit releases GDP and binds GTP activating it

3- the beta/gamma subunits dissociate

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24
Q

How does the dissociation of an activated alpha subunit allow for amplification

A

the receptor is still activated and can bind to a new g protein

1 receptor can activate many g proteins

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25
How do G proteins get ready to interact w another GPCR
after the activated G-proteins transduce the signal they turn themselves off using their intrinsic GTPase the inactive alpha subunit reassembles w the beta/gamma subunit
26
What are the 2 main secondary messengers produced
Adenylyl Cyclase -> Cyclic AMP (cAMP) Phospholipase C -> Inositol 1,4,5 triphosphate (IP3) AND diacylglycerol (DAG)
27
What are GEFS
Guanine nucleotide exchange factors; activate GTP-binding proteins and promote the release of bound GDP
28
What are GAPs
regulator protein that increases the rate of hydrolysis of bound GTP
29
How does cAMP pass information down the signalling pathway
it activates a cAMP dependent protein kinase A (PKA) causes a conformational change and releases 2 catalytic subunits
30
What is the structure of cAMP dependent protein kinase A (PKA)
it has 4 subunits; 2 regulatory and 2 catalytic that is inactive while bound
31
What is the function of phosphatases
to remove the phosphate from phosphorylated proteins
32
What does phosphorylation of proteins do to their function
switch them on and off
33
What is a kinase cascade
a protein kinase activated by phosphorylation which then phosphorylates the next protein
34
What is the importance of epinephrin
it activates glycogen phosphorylase which is inactive without phosphate it then hydrolyses glycogen to glucose 1-phosphate
35
Describe the epinephrine signalling pathway
1- epinephrine activates the GPCR, activating the G-protein 2- adenylyl cyclase converts ATP -> cAMP which activates PKA 3- a phosphorylation cascade phosphorylates glycogen phosphorylase
36
How is IP3 and DAG produced
the activated G-protein activates phospholipase C phospholipase C then cleaves phosphoinositol 4,5 -bisphosphate ( PIP2) to produce IP3 and DAG
37
What does IP3 casue?
the release of Ca2+ from the endoplasmic reticulum
38
What do Ca2+ and DAG do
they activate protein kinase C (PKC)
39
Why is Ca2+used as a secondary messenger
the cytosolic Ca2+ are relatively low compared to extracellular levels therefore small changes are easily detected
40
What mediates the effects of Ca2+
Calmodulin
41
How does calmodulin function
the molecule can bind 4 Ca2+ ions this results in a conformational change allowing the calmodulin/Ca2+ complex to wrap around the target protein this activates the protein
42
Describe the structure of enzyme-linked receptors
single span transmembrane protein with an intracellular and extracellular domain the cytosolic has intrinsic enzymatic activity or is associated w an enzyme
43
What is a receptor tyrosine kinase (RTK)
the most common type of enzyme liked receptors they have intrinsic kinase activity
44
Describe what happens when a ligand binds to an enzyme linked receptor
the binding causes cross-linking of 2 receptor chains this oligomerisation allows cross-phosphorylation (autophosphorylation) i.e phosphorylate each-other
45
What is autophosphorylation
when the domain can phosphorylate itself
46
What is cross-phosphorylation
when each domain can phosphorylate another domain
47
What is RAS
a small monomeric G protein main signal transducer for growth factors
48
Describe how RAS is activated
Its inactive when GDP is bound, this is released by GEF allowing GTP to bind the GTP is the hydrolysed by GAP and it's weak intrinsic GTPase activity
49
Why does RAS require a linker
Because it's not directly linked to the receptor
50
What benefits do phosphorylated tyrosine residues have
they provide docking sites for other signalling proteins on the receptor
51
What binds RAS and GEF to the RTK
mediated by an adaptor protein Grb-2
52
What is a MAP
mitogen activator protein
53
Describe the MAP kinase pathway
RAS activates a downstream phosphorylation cascade which can change protein activity or gene expression
54
Describe the steps in the MAP kinase pathway
1- RAS activates MAPKKK (Raf) 2- MAPKKK activates MAPKK (Mek) 3- MAPKK activates MAPK (Erk) 4- MAPK activates MAPs by phosphorylating the MAP protein
55
How can a mutation in RAS lead to cancer
RAS is a proto-oncogene the mutation usually in GTP hydrolysis activity; the GTP stays bound longer and the cycle is continuous Can cause cell proliferation even in the absence of growth factors
56
What is an inhibitor
a molecule that can target specific sites in pathway to inactivate it usually come as monoclonalantibodies
57
How can different cells respond differently to the same signal
- using different receptors | - activating different intracellular machinery
58
What are the receptors classes ad based on their speed
Ion channel linked receptor; ionotropic/ fast GPCR: metabotropic/ slow
59
Can signalling pathways interact
yes- different responses need different combinations of signals
60
What is cell crosstalk
when there is an overlap between different signalling pathways i.e secondary messengers shared and signalling proteins
61
What are the pro vs con of cell cross-talk
pro: allows the fine tuning of a response con: runs the risk of producing the wrong responses
62
What are the effects of signals combining
- they can activate a protein | - they can alter the activity of signalling protein
63
What are the different coordination's of signals possible
Additive; 1+1+2 Synergism; 1+1 >2 i.e increased effect Antagonism; 1+1< 2 i.e blocked effect
64
What are the 3 types of signalling complexes
1- stable; components of the signalling pathway are linked by a scaffold protein 2- transient; complex assembles after receptor is activated 3- transient; modification of plasma phospholipid molecules
65
What is a scaffold protein
molecule that brings together interacting proteins into signalling complexes
66
Describe how a signal is removed
1- degradation 2- recycling 3- sequestration
67
What affects the duration of a response
the rate at which the signal is removed
68
What are the ways of removing a receptor
1- receptor sequestration; it's temporary as the receptor is held in an endosome 2- receptor down regulation; permanent as the receptor is degraded by a lysosome

Biomedicine Semester 1 (2 decks)

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