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BIOL2200 - Cytoskeleton > Cellular Signalling > Flashcards

Cellular Signalling Flashcards

1
Q

What does the Ca2+/CaM switch do?

A

Non-covalent binding of the Ca2+/CaM to a kinase opens catalytic sites on the kinase allowing it to phosphorylate its substrate -> increase in ca2+ acts as “on” switch

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2
Q

What is the purpose of the GTPase switch?

A

GTPase is an enzyme that hydrolyses GTP -> GDP

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3
Q

What is Guanine Nucleotide Exchange Factor?

A

GEF – speeds up the replacement of GDP with GTP (Confers switch turning ON)

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4
Q

What is GTPase Activating Protein?

A

GAP – Increases GTPase activity (confers switch turning OFF)

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5
Q

What are the effects of acetylation on chromatin?

A

Unacetylated -> Chromatin highly condensed (heterochromatin) -> no expression

Acetylated -> chromatin less condensed (Euchromatin) -> expressed

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6
Q

What is a disease associated with nucleus?

A

Laminopathies – mutations that impact lamins

  • Muscular dystrophies & cardiomyopathies
  • Partial lipodystrophy
  • Peripheral and sensory neuropathies
  • Premature aging
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7
Q

What is Progeria?

A

Premature aging caused by the overexpression of Progerin gene

  • Mutations cause accumulation of unprocessed lamins or misprocessed lamins
  • There is a little progerin in all individuals -> increases with age
  • HGPS individuals have high levels of progerin at birth
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8
Q

What signal tends to act on membrane receptors?

A

Hydrophilic signals tend to act on membrane receptors (as they cannot pass through membrane)

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9
Q

What signal tends to act on cytosolic receptors?

A

Hydrophobic signals tend to act on cytosolic receptors (as can pass through membrane)

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10
Q

What are the four key steps in signal transduction?

A
  1. Conformational Change,
  2. Signal relay and amplification,
  3. Effector protein mediates cellular response,
  4. Signal shutdown.
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11
Q

What happens in the first stage of signal transduction?

A

What happens in the first stage of signal transduction?

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12
Q

What can signal transduction do to cells?

A

Signal transduction can cause the cell to mature and differentiate, move, acquire/lose specific functions and die (apoptosis)

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13
Q

How does Endocrine signaling work?

A

Hormone secreted into blood by endocrine gland -> hormone binds to receptors of the target cells (long distance signaling)

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14
Q

How does paracrine signaling work?

A

Ligands released by secretory cells which act on receptors of nearby target cells

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15
Q

How does autocrine signaling work?

A

Ligands released by cell act on its own receptors

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16
Q

How does juxtracrine signaling work?

A

Signaling cell has plasma-membrane-attached proteins which make contact with receptors on adjacent cells (i.e. cells must be in contact)

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17
Q

What does the cell surface receptor allow?

A

Allows water soluble ligand binding (e.g. growth factors, hormones)

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18
Q

What do cytoplasmic / nuclear receptors allow?

A

Binding of lipophilic molecules that can pass through membrane (e.g. steroids)

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19
Q

What are some examples of second messengers?

A
  • cAMP
  • cGMP
  • DAG
  • IP3
  • Ca2+
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20
Q

What are effector proteins?

A

Effector proteins are proteins that can bring about a cellular response (e.g. kinases, phosphatases, metabolic enzymes)

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21
Q

How do second messengers and signaling proteins allow for signal amplification?

A

Production of lots of second messengers in response to a signal -> each second messenger molecule might activate a signaling protein -> might activate number of downs tread further second messengers -> massive amplification (like a pyramid scheme)

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22
Q

How are signals recognized by effector proteins?

A

Signaling proteins and messengers move signal around the cell to convert it to a format understood by effector protein

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23
Q

What are the three primary means by which conformational changes are triggered?

A
  • Allosteric modification
  • Covalent modification
  • Cleavage (proteolysis)
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24
Q

What are allosteric modifications?

A

Molecule binds non-covalently to protein, alters protein conformation

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25
Q

What are covalent modifications?

A

Modification of chemical structure of target protein – this process can be reversible (e.g. Phoshporylation, ubiquitination, Lipidation, SUMOylatio)

26
Q

What is Lipidation?

A

Transfer of fatty acid group to protein, which enhances protein hydrophobicity

27
Q

What is SUMOylation?

A

The addition of small SUMO peptides which can alter protein function/localisation

28
Q

What is Proteolysis?

A

Protein cleaved by protease protein – this is not reversible and activate or inactivate protein
• Insulin produced by cleavage of precursor protein called pro-insulin
• Some proteases activated by cleavage

29
Q

What are some effects protein modification can have?

A
  • Activate enzyme activity
  • Unmask active sites
  • Alter protein localisation
  • Facilitate protein-protein interactions
  • Alter protein stability
30
Q

What are GPCRs components?

A
  • 7 Trans-membrane Alpha-Helix Domains
  • 4 Cytosolic Domains
  • 4 Extracellular Domains
31
Q

How are GPCR’s activated?

A
  • Hormones
  • Metabolites
  • Light
32
Q

What are the sub-units of Trimeric G-Protein Complexes?

A
  • Alpha (GDP/GTP bind here)
  • Beta
  • Gamma
33
Q

GPCR Effector Pathways

A
  • Adrenylate Cyclase
  • cAMP
  • Protein Kinase A

&

  • Phospholipase C
  • Protein Kinase C
  • Calcium
  • Calmodulin
34
Q

What does the ligation of GPCR cause?

A
  • Triggers a structural change that enables the following receptor functions:
    o Converts the inactive receptor to a Guanine-Nucleotide Exchange Factor (GEF)
    o Allows the receptor to interact with the trimeric G-Protein Complex to initiate signalling
35
Q

How many different subunits do humans have?

A
  • 21 different G-Alpha subunits (gas, gai, gaq)
  • 6 different G-Beta subunits
  • 12 different G-Omega (y) subunits
36
Q

Which GPCR subunits activate effectors?

A
  • Usually activated by G-Alpha – but this is not always the case as some ion channels are activated by the G-Beta-Omega (G-B-Y) Complex after it dissociates
37
Q

What is Adenylate Cyclase’s structure?

A
  • A multi-pass trans-membrane protein with two cytosolic and two catalytic domains
38
Q

What happens with Adenylate Cyclase interacts with GaS?

A
  • Interaction with GaS induces a conformational change allowing ACs two cytosolic catalytic domains to interact forming an active site
39
Q

What happens when Adenylate Cyclase interacts with G-aI?

A
  • Interaction with GaI induces a conformational change forcing the catalytic domains away from each other
40
Q

Which intracellular loop and terminal tail are phosphorylated, and by what kinase?

A

Activated GPCRs are phosphorylated on the 3rd intracellular loop and C-terminal tail by GPCR-Kinases (GRKs)

41
Q

Describe three mechanisms by which GPCR signalling is turned off?

A
  1. Arrestin proteins – direct GPCR for internalisation, leading to either recycling of the dephosphorylated inactive GPCR to the plasms membrane, or degradation
  2. A interaction between G-alpha and its effector protein increases GTPAse activity (GTP->P+GDP) – this returns the trimeric G-Protein to its “off” state
  3. By turning off secondary messengers (cAMP and IP3)
42
Q

What is the process for Hydrophobic Signalling?

A

• Steroids, Retinoids, Thyroxines -> Cytosolic Receptor -> Modification of gene expression development in the nucleus

43
Q

What is the process of Hydrophilic Signalling?

A

• Small molecules, peptides, proteins -> attach to cell-surface receptor -> Signal transduction proteins and second messengers -> effector protein -> ONE OF: modification of cellular metabolism, function, movement -> OR -> Modification of gene expression and development

44
Q

Receptor tyrosine kinase (RTK)

A
  1. inactive RTK
  2. Ligan binds->dimerization, kinase activation
  3. Active RTK-> autophosphorylation of tyrosine residues (cross phosph)
  4. Binding/activation of signaling proteins->initiation of cascade
45
Q

MAP kinase cascade

A

Mitogen-activated protein kinase cascade

  1. adaptor protein
  2. Ras activation protein
  3. active Ras
  4. activated MAPKKK (serine/threonine kinase)
  5. activate to MAPKK, threonine/tyrosine)
  6. activate to MAPK - effector protein (serine/threonine kinase)
  7. Phosphorphylates cystolic membrane proteins of nuclear gene regulatory protein
  8. Change in cystolic/membrane proteins or change in gene expression
46
Q

Cytokine receptor mechanism

A
  1. Inactive
  2. Cytokine binds–> dimerization of JAK
  3. JAK cross phosph, subunit phosphorylation
  4. STATs bind to subunit
  5. Phosphorylation of STATs, activated
  6. STATS dissociate and dimerize
  7. Translocation to nucleus–> altered gene expression
47
Q

Cytokine receptor termination

A

phosphatases remove tyrosine phosphates from receptor/STATS
SOCS (suppressor of cytokine signaling) protein inhibit STAT phsophorylation by binding/inhibiting JAKs or competing with STATs for phosphotyrosine binding sites on receptor
-multimeric formation of receptor after ligan binding triggers endocytosis of ligand receptor complex

48
Q

G protein coupled receptor mechanism

A
  1. ligand binds
  2. Conformational change, recognition site exposure for G protein binding
  3. GDP/GTP exchange, G protein alpha dissociates from beta-gamma
  4. Subunit alpha binding to enzyme (release second messengers)
  5. Intrinsic GTPase activation, hydrolysis of GTP to GDP, release enzyme
  6. G-protein reformation with GDP, returns to receptor
49
Q

G protein coupled receptor termination

A

extracellular enzymes metabolize or inactivate many of the small ligands

  • Receptor mediated endocytosis accounts for some desensitization
  • receptor phosphorylation by protein kinases is the major mechanism of sensitization
  • protein kinase A–> receptor +/- ligand
  • GPCR specific protein kinases (GRKs)->receptor +ligand
50
Q

cAMP action

A

ligand binds to G protein and sends alpha subunit w/ bound GTP binds to adenylate cyclase, which w/ ATP produces cAMP, which binds to receptors
Regulation: Depending on which G protein is activated can gave +/- effect

51
Q

cAMP termination

A

cAMP phosphodiesterase w/ h20 makes 5’-AMP

52
Q

What is the function of IP3?

A

Interacts with IP3 receptors on the ER to release intracellular store of Ca2+. Ca2+ activates PKC.
PKC translocates to the plasma membrane where it becomes activated by DAG.

53
Q

What are some of the functional roles of Ca2+

A

Can bind to the calcium binding protein calmodulin to activate calcium-dependent protein kinases e.g CaM Kinases
Ca2+ can cause muscle contraction
Ca2+ can influence gene expression

54
Q

what is the diff b/w a RTK and GPCR?

A

GPCRs have 7 transmembrane segments

RTKs have a single transmembrane segment, but each RTK functions as a dimer so it has a total of 2

55
Q

RTKs are involved in the regulation of what processes?

A

Growth (growth factor receptors), trigger mitosis

Cell division (defects lead to cancer)

Cell survival and death (programmed)

Cell attachments, migrations

56
Q

what are the 2 ways RTKs dimerize?

A

1 ligand binding to both monomers (ligand causes dimerization)

each monomer binds their own ligand & the 2 monomers come together

57
Q

what does dimerization trigger in RTKs?

A

auto-phosphorylation

the 2 monomers phosphorylate each other

58
Q

EF Hand Domain

A

Characteristic: Binds Calcium

Cellular Process: Calcium Dependent

59
Q

SH2 / PTB Domain

A

Characteristic: Binds Phospho-tyrosine

Cellular Process: Tyrosine Kinase Pathways

60
Q

PH Domain

A

Characteristic: Binds Phospho-inositides

Cellular Process: Recruitment to membranes and motility

61
Q

C1 Domain

A

Characteristic: Binds Diacylglyercrol

Cellular Process: Recruitment to membranes

BIOL2200 - Cytoskeleton (2 decks)

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