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MBB 231 > Lecture 22 - Cell Signalling & Transduction II > Flashcards

Lecture 22 - Cell Signalling & Transduction II Flashcards

1
Q

what are the 3 kinds of receptors?

A
  1. ligand-gated channels
  2. plasma membrane receptors
  3. nuclear receptors
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2
Q

what are the 2 kinds of plasma membrane receptors?

A
  1. those linked to G proteins
  2. those linked to protein kinases
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3
Q

members of the GPCR superfamily, the largest superfamily in the human genome, have ____ _____________ ____ ____________-

A

7 transmembrane alpha-helices

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4
Q

what does variation of G-protein linked receptors amino acid sequences lead to?

A
  • the extracellular portion of each receptor has a unique messenger binding site
  • the cytosolic portion allows the receptor to interact with only certain types of G proteins
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5
Q

what are some examples of signalling molecules?

A
  • proteins
  • peptides
  • amino acid derivatives
  • fatty acids
  • photons
  • olfactory molecules
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6
Q

three extracellular loops act as the ________ _________ ____________ and these structures can vary among different GPCRs

A

ligand binding pocket

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7
Q

three intracellular loops provide ________ ________ for signalling proteins, including the ___________ ______ ______________-

A

binding sites, heterotrimeric G-protein

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8
Q

what is the job of the receptor and how does it do it?

A

transfer an extracellular signal across the membrane, does this by altering the confornatio

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9
Q

what is the job of the receptor and how does it do it?

A

transfer an extracellular signal across the membrane, does this by altering the conformation

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10
Q

def: non covalent interactions within the transmembrane alpha-helices stabilizes the inactive structure and bury the G-protein binding sites

A

inactive state

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11
Q

def: ligand binding disrupts transmembrane interactions, rotating these alpha-helices, causing the cytoplasmic loops to “unmask” G-protein binding sites

A

active state

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12
Q

what are the 2 classes of GTP proteins?

A
  • small monomeric G proteins
  • large heterotrimeric G proteins
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13
Q

where are heterotrimeric G proteins held and how?

A

in the plasma membrane by the covalent attachment of lipid chains

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14
Q

what are the 3 parts of the heterotrimeric G protein?

A

alpha, beta, gamma subunits

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15
Q

which part of the heterotrimeric G protein associates with the GDP/GTP molecule?

A

the G-alpha subunis, this portion binds and hydrolyzes GTP/GDP

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16
Q

what happens when a ligand binds to a GPCR?

A

the receptor undergoes conformation change that unmasks the binding site allowing G protein association

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17
Q

what does the binding of the G-protein to the GPCR do?

A

induces conformational change in G-alpha, causing the release of GDP and binding of GTP

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18
Q

what happens to G-alpha after it is GTP bound?

A

G-alpha has low affinity for G-beta/G-gamma which leads to dissociation of the trimeric complex, G-alpha can now freely activate the effector protein

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19
Q

what does activation of the effector lead to?

A

production of a second messenger which activates more intracellular signalling proteins

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20
Q

what will eventually happen to the G-alpha protein associated with the effector?

A
  • the G-alpha subunit will eventually hydrolyze the GTP, into GDP + Pi,
  • once hydrolyzed to GDP = SWITCH OFF
  • G-alpha conformational change, reducing its affinity for effector, and increasing affinity for G-beta/G-gamma
21
Q

what does the G-beta/G-gamma subunit do?

A
  • can also transduce signals
  • they can associate with K+ channels and open the gate
22
Q

what does the cell do to prevent overstimulation of GPCRs?

A

the cytoplasmic of GPCRs are phosphorylated by G-protein coupled receptor kinases (GRKs)

23
Q

what does phosphorylation of GPCRs do?

A
  • increase their affinity for Arrestins, which compete with the heterotrimeric G proteins for binding
24
Q

def: cells stop responding to the stimulus despite the continued presence of stimulus on its outer surface

A

desensitization

25
Q

what are the 3 alternative outcomes of termination?

A
  1. receptor can resume signalling within the endosome
  2. receptor can be traffic to the lysosome for degradation
  3. the receptor can be returned to the cell surface where the phosphorylation sites must be removed
26
Q

def: if a receptor returns to the cell surface, they can resume signalling

A

re-sensitization

27
Q

one of the most important and widespread signalling events, regulated by different GPCRs, involves the release/formation of ___________ ____________

A

second messengers

28
Q

def: formed from cytosolic ATP by adenyl cyclase, an enzyme is anchored in the plasma membrane

A

cyclic AMP (cAMP)

29
Q

adenyl cyclase is inactive until bound by an active _________, subunit of specific

A

G-alpha

30
Q

def: a stimulatory G-alpha protein, activated by binding of a ligand to a specific GPCR

A

G-alpha S

31
Q

adenyl cyclase =
phosphodiesterase =

A

adenyl cyclase = generates cAMP
phosphodiesterase = degrades cAMP

32
Q

how does phosphodiesterase function work within the cell?

A

it is constantly being produced but when an effector is activated and generating secondary signals, they outnumber the phosphodiesterase.

33
Q

what is the main target of cAMP

A

Protein Kinase A, where it acts as an allosteric activator, and regulates the separation of the regulatory and catalytic subunits

34
Q

def: phosphorylates a variety of proteins on serine or threonine residues, using ATP as the source of phosphate

A

PKA

35
Q

how does cAMP activate PKA’s?

A

it binds to their regulatory subunits, causing them to change conformation
then the catalytic subunits detach and are now activated and can phosphorylate target proteins in the cell

36
Q

cAMP stimulates the ____________ of the enzyme system responsible for synthesis of ___________, as PKA phosphorylates glycogen synthase to inactivate it

A

inactivation, synthesis of glycogen

37
Q

PKA also activates ____________ ______________, which activates ___________ _________, which catalyzes the cleavage of glycogen into glucose 1-phosphate, leading to glucose release

A

phosphorylase kinase, glycogen phophatase

38
Q

how does PKA choose what proteins to activate?

A
  1. different cells express different PKA substrates
  2. AKAPS (A Kinase-Anchoring Proteins) acts as signalling hubs, sequestering PKA to specific locations within the cell)
39
Q

def: provide scaffolding for coordinating protein-protein interactions by sequestering PKA to specific cellular locations

A

AKAPs

40
Q

when cAMP levels rise, _____ is activated

A

PKA

41
Q

which substrates are the first ones to become phosphorylated?

A

the ones present in close proximity

42
Q

what does the activation of enzyme phospholipase C trigger?

A

the cleavage of the relatively uncommon membrane phospholipid PIP2

43
Q

what does PIP2 generate?

A

IP3 and DAG, function as second messengers in a variety of cellular events

44
Q

lipids cleaved from the membrane are used as _________ __________

A

second messengers

45
Q

briefly describe the IP3 and DAG second messenger process?

A
  1. ligand binds to membrane receptor
  2. activates specific G protein, G-alpha-q
  3. G-alpha-q actives a phospholipase which cuts PIP2 into IP3 and DAG
  4. IP3 diffuses through the cytosol and binds a ligand gated calcium channel, the IP3 receptor channel
46
Q

how are cytoplasmic Ca2+ concentrations maintained at low levels?

A
  1. Ca2+ ions channels are closed
  2. Na+/Ca2+ antiporters and calcium ATPases in the plasma membrane and SER actively transport Ca2+ out of the cytosol
47
Q

how can signalling increase cytosolic [Ca2+]?

A
  1. voltage gated Ca2+ channels opened by nerve impulses
  2. IP3 receptor channels can open upon IP3
  3. Ryanodine receptor channels are sensitive to calcium (calcium induced release)
48
Q

how do Calmodulin and Ca2+ ions interact?

A

Calmodulin binds to 2 Ca2+ ions, changes its conformation and the increases its affinity for a variety of effectors
Goes from S shaped to U shaped

MBB 231 (19 decks)

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