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BIOL 2020 > Signalling > Flashcards

Signalling Flashcards

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1
Q

Two types of signaling pathways

A
  1. GPCRs - receptor activates an effector which releases a second messenger.
  2. RTKs - receptor is phosphorylated so other proteins come to it to get activated.
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2
Q

GPCR structure overview

A

seven transmembrane domains (α-helices)
Three loops on each side with the exoplasmic loops being quite variable to recognise a wide variety of ligands.

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3
Q

G proteins are ______

A

GTPases!

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4
Q

Monomeric g-proteins

A

Ran, Sar1, Arf1

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5
Q

GPCR generalised pathway

A
  1. Ligand binds the receptor, binds a G protein, induces Gα to release GDP and acquire GTP.
    2.Dissociation of subunits.
  2. Gα inhibits or activates targets, initiates transduction.
  3. Gα hydrolyses GTP to GDP, and inactivates.
  4. Subunits recombine to form an inactive G protein.
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6
Q

Guanine exchange factors

A

Exchange a GDP with a GTP to make proteins turn on faster.

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7
Q

the GPCR is a ____ for the G proteins

A

GEF!!

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8
Q

GTPase activating proteins

A

Help the protein to hydrolyse faster and turn off.

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9
Q

RGSs

A

Regulators of G protein signalling, involved in the GPCR pathway to end stimulation of the effector more rapidly.

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10
Q

Desensitisation

A

Termination of the GPCR, performed by G protein receptor kinases and arrestin.

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11
Q

Arrestin

A

Binds the phosphorylated GPCR to bring in the AP2 adaptors.

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12
Q

AP2 adaptors

A

recruit the clathrin coat, involved in the endocytosis of the GPCR to cause desensitisation.

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13
Q

Three pathways for endocytosed GPCRs

A

Recycled, lysosome, other cytosolic pathways.

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14
Q

Second messengers are ;

A

Generated by effector enzymes, small, non-protein molecules that rapidly diffuse inside a cell to activate one or more signalling molecules.

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15
Q

Adenylyl cyclase

A

An effector enzyme that makes cAMP from ATP.

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16
Q

Mechanism of cholera toxin

A

Modifies the Gα so t cannot hydrolyse GTP to GDP. The G protein thus continues stimulating adenylyl cyclase to make cAMP, excess salt secretion leads to water loss and diarrhea.

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17
Q

Protein kinase A activation mechanism

A

Allosteric regulation.
Composed of two catalytic and regulatory subunits. cAMP activates by binding the Reg subunits so that they detach and the catalytic subunit is activated.

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18
Q

Fight or flight is an example of a response mediated by _______

A

cAMP and PKA

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19
Q

Biochemical pathway for fight or flight via cAMP/PKA

A
  1. Adrenaline
  2. GPCR
  3. G protein
  4. Adenylyl cyclase
  5. cAMP
  6. PKA
  7. CREB (transcription factor), and glycogen phosphorylase (enzyme)
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20
Q

CREB

A

A transcription factor that makes the anabolic enzymes that synthesis glucose from smaller precursors.

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21
Q

Lipid derived second messengers are made by 3 different effector enzymes

A

Phospholipid kinases
Phospholipid phosphorylases
Phospholipases (split lipids)

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22
Q

Phosphatidylinositol

A

PI - Has an inositol ring that can be phosphorylated by phospholipid kinases

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23
Q

Posphatidylinositol 4,5-bisphosphate (PIP2)

A

A phosphoinositide that is cleaved by phospholipase C to produce IP3 and DAG

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24
Q

If a protein has a _________ it will bind to the phosphorylated inositol rings of membrane-bound phosphoinositides

A

PH domain.

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25
Phospholipase C and IP3/DAG pathway
Gα activates PLC which cleaves PiP2 into IP3 & DAG - DAG remains in the membrane and recruits PKC - IP3 triggers Ca2+ release, which further activates PKC PKC will phosphorylated many targets.
26
Results of adding IP3 to permeabilised or intact cells
Calcium mobilisation, membrane depolarisation - Ca2+ is another second messenger released from the SER.
27
Calmodulin function
A calcium binding protein with four Ca2+ binding sites but that has a low affinity so that it is only activated under high [Ca2+]
28
Protein kinase C function
Ubiquitous protein kinase
29
Receptor tyrosine kinase activation
Two receptors in the membrane that are actives through dimerisation.
30
Two pathways for RTK dimerisation
1. Ligand mediated dimerisation (single ligand binds two receptors at once) 2. Receptor mediated dimerisation (two ligands bind different receptors and induces dimerisation interface)
31
Transautophosphorylation
RTK activity of one receptor phosphorylates tyrosine residues in the other dimer, and vice versa.
32
Recruiting station of RTKs
Binds to the SH2 (Src-Homology 2) or PTB (Phospho-Tyrosine-Binding) domain on other proteins of which there are four classes.
33
Examples of proteins with SH2 or PTB domains
Adaptor proteins such as Grb2 in the Ras-MAP pathway Docking proteins Transcription factors Signaling enzymes
34
Ras protein overview
A small monomeric G protein that leads to cell proliferation when active (GTP bound), 30% of all cancers have Ras always ON.
35
Ras protein location
Anchored at the inner surface of the plasma membrane by a lipid group
36
Ras-MAP pathway to active Ras
RTK - Grb2 - Sos - RasGTP
37
Pathway following Ras-GTP activation
Ras-GTP binds membrane-bound Raf, Raf then phosphorylates MEK which phosphorylates ERK which then turns on transcription factors
38
Transcription factors of the Ras-MAP pathway
Ets and Jun in th nucleus. Involved in cell proliferation.
39
Regulation of RasMAP pathway
MKP-1, one of the genes that is transcribed) dephosphorylates ERK to stop further signaling. (Negative feedback examples)
40
Raf
MAP Kinase Kinase Kinase
41
MEK
MAP kinase kinase
42
ERK
MAP kinase
43
MAP stands for
Mitogen activated pathway
44
Protooncogenes
Genes that have the potential to push the cell towards the malignant state
45
Oncogenes
Gene that encodes for a protein that promotes loss of growth control
46
Model organism used to study apoptosis
C. elegans, a transparent round worm about 1mm long. Highly specific amount of cells produced during development (1090), absolute precision.
47
Horvitz, Brenner, Sulston
2002 nobel prize for determining the precise order in which C. elegans is divided, and figured out that of the 1090 cells produced, 131 are programmed to die.
48
Key proteins in the apoptitic pathway are named as …
ced (CEll Death)
49
Features of apoptosis
Cell shrivels, becomes lobed. Loss of adhesion. Fragmentation of organelles. DNA digestion in intervals (laddering) Blebs. Eat me signal (phosphotidylserine)
50
DNA laddering
Digestion of DNA at regular intervals by DNases.
51
Necrosis characteristics
Cell swells Organelles swell Cell contents leak into the surrounding fluid, leading to inflammation
52
Caspases
Proteolytic enzymes (cysteine in the active site) that cleave target proteins at an aspartic acid residue
53
Horvitz
Discovered that the ced-3 protein is a cysteine protease.
54
Extrinsic triggers of apoptosis
Receptor in the membrane receives a death signal (usually a cytokine from an activated macrophage such as FasL)
55
Intrinsic signals of apoptosis
Radiation Oxidative stress High cytoplasmic [Ca2+]
56
Extrinsic apoptosis pathway
Death signal binds membrane receptor and recruits adaptor proteins as well as two procaspase-8s. Procaspase-8s then cleave each other to make the mature enzyme. The initiator caspase initiates apoptosis by cleaving downstream caspases that lead to the execution caspase.
57
FasL
Death signal, a cytokine.
58
FasR
Death receptor. The Fas receptor in the plasma membrane, such as CD95.
59
FADD
Fas Associated Death Domain, adaptor protein in apoptosis pathway.
60
Pro caspase-8
cleave each other into caspase-8.
61
caspase-8
An initiator caspase which cleanse and activates other caspases
62
Caspase-3
Executioner caspase
63
Mitochondrial mediated apoptosis
Intrinsic apoptitic pathway
64
Mechanism for the intrinsic apoptitic pathway
Survival factor binds an RTK, causing BAD to be phosphorylated, which then inhibits anti-apoptitic proteins Bcl-2 and Bcl-X, BAX channels then opens and cytochrome C is released from the mitochodria.
65
Bcl-2 and Bcl-x
Anti-apoptosis proteins that normally keep the BAX channel closed. Normally inhibited by BAD.
66
BAD protein
inhibits Bcl-X and Bcl-2 but only when it is in its unphosphorylated form
67
Pro-apoptitic protein
BAX (channel protein i the mitochondria membrane)
68
Anti-apoptitic protein
BCL-2 and BCL-x, normal function is to inhibit the BAX channel
69
Role of cytochrome C in apoptosis
Joins the apoptosome
70
Effects of free BAD proteins
Will have lost is phosphates and thus will capture the anti-apoptosis proteins Bcl-x and Bcl-2
71
Apoptosome components
Cytochrome C Apart-1 Pro caspase-9
72
Pro-caspase 9
Another initiator caspase
73
Anastasis
Cells hold onto a life line whilst undergoing apoptosis so that they may recover if conditions improve.
74
The discovery of GPCRS
Was in yeast, during mating they trigger each other to induce fusion

BIOL 2020 (8 decks)

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