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Biomedicine Semester 1 > Cell Signalling > Flashcards

Cell Signalling Flashcards

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
Q

How do G proteins get ready to interact w another GPCR

A

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

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26
Q

What are the 2 main secondary messengers produced

A

Adenylyl Cyclase -> Cyclic AMP (cAMP)

Phospholipase C -> Inositol 1,4,5 triphosphate (IP3) AND diacylglycerol (DAG)

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27
Q

What are GEFS

A

Guanine nucleotide exchange factors; activate GTP-binding proteins and promote the release of bound GDP

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28
Q

What are GAPs

A

regulator protein that increases the rate of hydrolysis of bound GTP

29
Q

How does cAMP pass information down the signalling pathway

A

it activates a cAMP dependent protein kinase A (PKA)

causes a conformational change and releases 2 catalytic subunits

30
Q

What is the structure of cAMP dependent protein kinase A (PKA)

A

it has 4 subunits; 2 regulatory and 2 catalytic that is inactive while bound

31
Q

What is the function of phosphatases

A

to remove the phosphate from phosphorylated proteins

32
Q

What does phosphorylation of proteins do to their function

A

switch them on and off

33
Q

What is a kinase cascade

A

a protein kinase activated by phosphorylation which then phosphorylates the next protein

34
Q

What is the importance of epinephrin

A

it activates glycogen phosphorylase which is inactive without phosphate

it then hydrolyses glycogen to glucose 1-phosphate

35
Q

Describe the epinephrine signalling pathway

A

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
Q

How is IP3 and DAG produced

A

the activated G-protein activates phospholipase C

phospholipase C then cleaves phosphoinositol 4,5 -bisphosphate ( PIP2) to produce IP3 and DAG

37
Q

What does IP3 casue?

A

the release of Ca2+ from the endoplasmic reticulum

38
Q

What do Ca2+ and DAG do

A

they activate protein kinase C (PKC)

39
Q

Why is Ca2+used as a secondary messenger

A

the cytosolic Ca2+ are relatively low compared to extracellular levels

therefore small changes are easily detected

40
Q

What mediates the effects of Ca2+

A

Calmodulin

41
Q

How does calmodulin function

A

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
Q

Describe the structure of enzyme-linked receptors

A

single span transmembrane protein with an intracellular and extracellular domain

the cytosolic has intrinsic enzymatic activity or is associated w an enzyme

43
Q

What is a receptor tyrosine kinase (RTK)

A

the most common type of enzyme liked receptors

they have intrinsic kinase activity

44
Q

Describe what happens when a ligand binds to an enzyme linked receptor

A

the binding causes cross-linking of 2 receptor chains

this oligomerisation allows cross-phosphorylation (autophosphorylation) i.e phosphorylate each-other

45
Q

What is autophosphorylation

A

when the domain can phosphorylate itself

46
Q

What is cross-phosphorylation

A

when each domain can phosphorylate another domain

47
Q

What is RAS

A

a small monomeric G protein

main signal transducer for growth factors

48
Q

Describe how RAS is activated

A

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
Q

Why does RAS require a linker

A

Because it’s not directly linked to the receptor

50
Q

What benefits do phosphorylated tyrosine residues have

A

they provide docking sites for other signalling proteins on the receptor

51
Q

What binds RAS and GEF to the RTK

A

mediated by an adaptor protein Grb-2

52
Q

What is a MAP

A

mitogen activator protein

53
Q

Describe the MAP kinase pathway

A

RAS activates a downstream phosphorylation cascade which can change protein activity or gene expression

54
Q

Describe the steps in the MAP kinase pathway

A

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
Q

How can a mutation in RAS lead to cancer

A

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
Q

What is an inhibitor

A

a molecule that can target specific sites in pathway to inactivate it

usually come as monoclonalantibodies

57
Q

How can different cells respond differently to the same signal

A
  • using different receptors

- activating different intracellular machinery

58
Q

What are the receptors classes ad based on their speed

A

Ion channel linked receptor; ionotropic/ fast

GPCR: metabotropic/ slow

59
Q

Can signalling pathways interact

A

yes- different responses need different combinations of signals

60
Q

What is cell crosstalk

A

when there is an overlap between different signalling pathways i.e secondary messengers shared and signalling proteins

61
Q

What are the pro vs con of cell cross-talk

A

pro: allows the fine tuning of a response
con: runs the risk of producing the wrong responses

62
Q

What are the effects of signals combining

A
  • they can activate a protein

- they can alter the activity of signalling protein

63
Q

What are the different coordination’s of signals possible

A

Additive; 1+1+2

Synergism; 1+1 >2 i.e increased effect

Antagonism; 1+1< 2 i.e blocked effect

64
Q

What are the 3 types of signalling complexes

A

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
Q

What is a scaffold protein

A

molecule that brings together interacting proteins into signalling complexes

66
Q

Describe how a signal is removed

A

1- degradation

2- recycling

3- sequestration

67
Q

What affects the duration of a response

A

the rate at which the signal is removed

68
Q

What are the ways of removing a receptor

A

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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