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Molecular & Cell Biology > Basics of Cell Signalling > Flashcards

Basics of Cell Signalling Flashcards

1
Q

What is a ligand?

A

-A signalling molecule
-Often a protein - bind to protein (receptor) inducing a confirmational change in shape

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2
Q

Examples of ligands?

A

-Neurotransmitters
-Pheromones
-Growth factors/cytokines
-Hormones

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3
Q

Other than a ligand binding to a rec. what is another way to cause a confirmational shape change?

A

Covalent Modifications

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4
Q

Basic cell signalling pathway?

A

-Specific ligand binds to specific receptor
= confirmational shape change
-This alters activity/protein function (fast)/changes in gene express (slow) = cell beh. changes (signal transduction pathway)

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5
Q

Types of ligand (x2)?

A

-Hydrophilic = attracts H2O/soluble in aq
-Hydrophobic = repels H2O/insoluble in aq

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6
Q

Explain ligand types - function?

A

-Plasma memb. = NOT aq
-Hydrophilic = can’t pass through - only if something else acts to move them
-Hydrophobic = can pass through memb easily

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7
Q

Location of receptors for hydrophilic ligands?

A

Bound to cell surface memb (ext) - rec site = extracellularly facing

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8
Q

Location of receptors for hydrophobic ligands?

A

Intracellular

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9
Q

What is a signal transduction pathway?

A

Converting the signal into a cellular response

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10
Q

Types of cell communication that are activated (based on how signal is transported) (x4)?

A

-Gap junction
-Paracrine signalling (Autocrine)
-Endocrine signalling
-Synaptic transmission

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11
Q

What is a gap junction?

A

-Direct route = pores in cytoplasms (connects x2 cytoplasms)
-Molecules move through to adj cell
-Regulated gate
-Intracellular signalling

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12
Q

What is paracrine signalling?

A

-Activated cell releases molecule travels locally to further act on

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13
Q

What is autocrine signalling?

A

-Seen in cancer
-GFs released from cell bind to recs on same cell = a cycle

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14
Q

What is endocrine signalling?

A

-E.g., insulin action
-Long distance signalling
-Ligand moved through body (e.g., bloodstream) to target organ

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15
Q

What is synaptic signalling?

A

-Ligand = neurotransmitter
-Local often - can be long dist.

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16
Q

Response - signal transduction pathway after signal/ligand transported to target?

A

-Ligand binds to rec (often protein)
= response(s) - no. depends on cell type- can rely on 2nd messenger

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17
Q

When ligand binds to rec how can proteins be activated/deactivated?

A

= Phosphorylation/dephosphorylation

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18
Q

What type of modification is phosphorylation/dephosphorylation?

A

Covalent

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19
Q

How is phosphorylation triggered by ligand binding?

A

-Activates protein kinases
-Remove Pi from ATP = energy to use (as bonds = high energy) - to +Pi to target protein
-i.e., ATP is dephosphorylated

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20
Q

How is dephosphorylation triggered by ligand binding?

A

-Activates protein phosphatases
-Pi removed from target protein = energy used to reform ATP
-i.e., ATP is phosphorylated

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21
Q

Structure of ATP?

A
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22
Q

Types of extracellular receptors?

A

-Chemically gated ion channels
-Enzymatic receptors
-G-protein coupled receptors

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23
Q

Role of extracellular receptors?

A

To pass extracellular signal to intracellular signal

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24
Q

What are chemically gated ion channels?

A

-Ligand = ion (in & out)
-Ligand binds = confirmational change in shape of pore = opens - ligand passes into cell
-Centre = hydrophilic - so ligands can pass through (dissolve?)
-Hydrophobic outside = so embeds in memb
-Multi-pass transmembrane protein (the shape)

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25
Q

What are enzymatic receptors?

A

-Ligand binds = confirmational change in shape of protein - triggers enzyme activation
-Single pass (->) - ext domain = binds to ligand
-Hydrophobic part = so embeds in memb
-Intracellular space = direct enz activity or ability to initiate

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26
Q

What ate G-protein coupled receptors?

A

=Trimeric G-protein complexes = a, b, y units
-Ligand binds = a unit splits off
-a unit binds to ion channel
-a unit exchanges its GDP for GTP = activates

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27
Q

Chemically gated ion channels vs enzymatic receptors

A

CGICs = both ways
ERs = single pass
CGICs = ligand = ion
-ERs = ?

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28
Q

What type of receptor is a receptor protein kinase?

A

Enzymatic

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29
Q

What feature must ligands of intracellular receptors have?

A

Ability to pass through cell surface memb

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30
Q

Where are intracellular receptors?

A

Cytoplasm or nucleus

31
Q

Role of intracellular receptors?

A

Affect change in gene expression

32
Q

What is an example of an intracellular receptor found in cytoplasm?

A

Steroid receptor

33
Q

What happens to a steroid receptor in absence of ligand (hormone)?

A

Heat shock proteins bind

34
Q

What are the 3 functional domains on a steroid receptor?

A

-Hormone binding domain
-DNA binding domain (binds to promotor)
-Domain that interacts with cofactors

35
Q

What is the purpose of the cofactor domain on steroid receptors?

A

To recruit proteins/other compounds needed for transcription

36
Q

What happens when ligand (hormone) binds to steroid receptor?

A

-Heat shock proteins released
-Receptors dimerise
-Move into nucleus
-Bind to promoters

37
Q

What is a homodimeric receptor?

A

In cytoplasm = -ve
Rec moves to nucleus & bind to promotor = +ve

38
Q

What is a heterodimeric nuclear receptor?

A

In nucleus
Deacetylation (@ nearby nucleosome) when bound to DNA = -ve
Confirmational shape change - so histone acetylase complexes bind = +ve

39
Q

What does -ve & +ve mean in relation to transcription?

A

-ve = -vely acts on/inhibits transcription
+ve = +vely acts on/promotes transcription

40
Q

Examples of heterodimeric receptors?

A
  • RXR-VDR
  • RXR-TR
  • RXR-RAR
41
Q

Mechanism of transcriptional activation in homodimer receptors?

A

-Steroid hormone passes through plasma memb from cytoplasm
-Binds to steroid rec (has heat shock protein complex bound) = confirmational change in shape - coregulatory exchange
-HSPC released
-Dimerises (hom/het)
-Steroid rec translocates to nucleus via nuc pore
-Binds to promoter (specific) - DNA binding site (response element)
-Initiates transcription

42
Q

What happens with heterodimeric transcriptional activation?

A

-Repressor protein complexes recruited when no ligand = so gene not expressed
-Ligand binds = conf change shape
-Repressor complex removed
-Activator complex recruited
-Gene activated

43
Q

Where are homodimer receptors when isn’t & is gene activation?

A

-Isn’t = cytoplasm
-Is = nucleus

44
Q

What happens when ligand binds to receptor tyrosine kinases?

A

Dimerisation (homo) of RTKs
= autophosphorylation of (intrinsic) tyrosines residue
-Tyrosine residues now = protein docking sites = phosphorylates these
-Adaptor proteins bind to docking proteins (= downstream sigs)

45
Q

Processes RTKs activate?

A

-Cancer
-Normal cellular processes
–> growth & cell division
-Neurodegenerative diseases

46
Q

Location of tyrosine kinases?

A

-Intracellular = TKs
-Embed in cell membs (as RTKs)

47
Q

Role of tyrosine kinases?

A

Phosphorylate proteins (as are enzs)
—- FOR:

48
Q

Why are RTKs targeted by cancers?

A

Involved in so many important cellular functions

49
Q

Example of where RTKs involved in major pathway?

A

Insulin (when blood glu = high)

50
Q

How do insulin receptors regulate blood glu when is too high?

A

-Insulin binds recs
-Vesicles of glu transporters fuse w/ cell memb
-Glu into cells

51
Q

What happens to glu transporters when blood glu drops?

A

-Glu transporters move out of cell memb - endocytosis
= forms vesicles
-which fuse w/ large endosome
-Smaller vesicles detach (contain glu transporters)

52
Q

How is glycogenesis generated?

A

-Insulin binds ext domain rec
-Autophos int domain (tyrosine residue)
-Insulin response/docking protein binds to tyrosine
-Activates glycogen synthase = glu-> glyc

53
Q

Role of adaptor/scaffold proteins in kinase cascades?

A

Bring together all enzymes for the cascade pathway = Grb2 in ERK signalling pathway

54
Q

What is a kinase cascade?

A

The passing down of activation (by phos) from initial tyrosine kinase (ENZYME) to other kinases (MAPKs) = phosphorylation cascade

55
Q

What is a kinase cascade starting from an adaptor protein binding to recs (e.g., Grb2)?

A

-Grb2 allows other proteins to bind (SOS, Ras)
-Initial phos of Grb2 by tyrosine kinase in rec
-Then phos each other
-Then phos MAPKs

56
Q

What is amplification in a kinase cascade?

A

-Ras activates the Raf kinase, which activates the MEK kinase, which in turn activates the ERK kinase - each enzyme acts on many substrates (of same type?) - 1 Raf kinase activates many Rafs then many MEK kinases activate even more MEK

57
Q

Besides from kinase cascade, how else can signal amplification occur?

A

-Using scaffold proteins
–> brings together all of the kinase cascade items (MAPKs) together (one place) on one protein
= more efficient

58
Q

3 ways signal amplification is achieved?

A

-Kinase cascades
-Scaffold proteins
-2nd messenger

59
Q

How does the 2nd messenger model amplify a signal?

A

-1st mess binds rec
-An enz makes lots of 2nd mess (ATP -> cAMP)
-Then activate target

60
Q

What mechanism/rec type does 2nd messenger use?

A

G-protein coupled rec

61
Q

Role of G-proteins - i.e., the subunits?

A

Activates effector (links rec to effector) - to produce 2nd messenger

62
Q

What happens in the signal transduction pathway when glucagon/adrenaline binds to its GPCR (G protein coupled receptor)?

A

-Causes exchange of GDP for GTP on G alpha (a) subunit
-a subunit splits off from b & y
-a binds to adenylyl cyclase (effector)
-Adenylyl cyclase catalyses conversion
ATP->cAMP (2nd mess)
-cAMP activates protein kinase A (PKA) - then cAMP degraded (reverse PKA activity)
-Kinase cascade
-Glycogen -> Glucose (inc blood glu) + 2 more for adrenaline only

63
Q

What 3 effects does adrenaline have?

A

-Breakdown glycogen->glucose (when binds to rec on liver & muscle cells)
-Inc heart rate - inc contraction strength (when binds rec on heart cells)
-Lipid hydrolysis - triacylglycerols -> FAs + glycerol (when binds rec on adipose cells)

64
Q

What type of GPCR for adrenaline?

A

B2AR (Beta 2 adrenergic rec)

65
Q

What is the 2nd mess in glucagon/adrenaline signal transduction?

A

cAMP

66
Q

What is the kinase cascade in glucagon/adrenaline signal transduction?

A

-PKA phosphorylates phosphorylase b kinase (activates)
-> which phosphorylates glycogen phosphorylase b -> glycogen phosphorylase a

67
Q

What are the 3 ways of regulating GPCR?

A

-Deactivation of a subunit (GTP->GDP) = G protein (caused by Gai)
-Internalise GPCRs (endo)
-Production of inhibitory G a subunit (Gai) - due to inhibitory ligand binding = inhibits adenylyl cyclase

68
Q

How is G protein activity regulated?

A

Contains intrinsic GTPase activity in a = hydrolyses GTP-> GDP to deactivates a

69
Q

How are GPCR (B2AR) internalised?

A

-b & y subunits dissociate
-recruit B(eta)ARK to memb
= phosphorylates ser residue @ carboxyl terminal
-B(eta)arr binds to phosphorylated part of rec
-Barr/rec complex endocytosis into cell = vesicle
-If want back in memb = Barr dissociates & rec dephos

70
Q

What are stimulative ligands of GPCRs, and what do they do?

A

-Glucagon
-Adrenaline
-Adrenocorticotropic hormone (ACTH)
–> generates Gas (activates adenylyl cyclase)

71
Q

What are inhibitory ligands of GPCRs, and what do they do?

A

-Prostaglandin E1 (PGE1)
-Adenosine
–> generates Gai (inhibits adenylyl cyclase)

72
Q

Other 2nd mess (x2) pathway (x1) that can produce from adrenaline signal transduction?

A

-Ga/GTP bind to phospholipase C (PLC) = activates
-PLC catalyses cleavage of PIP2 -> IP3
-IP3 can activate Ca2+ gated ion channels = Ca2+ into cell AND IP3 produces diacylglycerol (DAG)
-Ca2+ & DAG activate protein kinase C (PKC) (Ca2+ or Calmodulin)
2nd mess = IP3 & DAG

73
Q

What is the following an example of - ‘adrenaline has different effects on different cell types’?

A

How different recs can cause same transduction/2nd mess pathway in different cells but have different responses

Molecular & Cell Biology (4 decks)

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