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BMS100 test 1 > Intracellular signalling and the cell membrane > Flashcards

Intracellular signalling and the cell membrane Flashcards

1
Q

intracellular signals

A

receptors in cell membrane detect extracellular signals and modify cell function

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2
Q

transduction

A

intracellular events that transform the extracellular signal into an intracellular signal

thens there’s more signalling… 2nds messengers…

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3
Q

general intracellular singalling model

A
  1. 1st messenger binds receptor on extracellular domain, (has transmembrane and intercellular domain)
  2. activates enzymes
  3. activates 2nd messenger
  4. activate effectors
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4
Q

what activates effectors?

A

I.e. protein kinases, transcription factors

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5
Q

effector

A

2nd messenger binds and activates other protein, that protein activates another… cascade

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6
Q

amplification

A

increase 2nd messenger

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7
Q

signal termination; 3 ways

A

no 1st messenger or receptor

degrade 2nd messengers

negative feedback

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8
Q

3 types of cell membrane receptors

A
  1. ion channel coupled receptors
    –> signal molecule binds channel which allows entry into cell
  2. enzyme coupled protein receptors
    –> 2 domains of receptor are activated by a signal molecules that forms a dimer causing the catalytic domains to become active
    OR
    –> signal molecule binds receptor and the associated enzyme is activated
  3. g-protein coupled receptors
    –>activate G protein receptor through combining the g protein, enzyme and receptor via the signal molecule
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9
Q

GTPase

A

when GTP hydrolysed to GDP

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10
Q

how do you activate a GPCR receptor? what nucleotide binds the receptor?

A

guanine nucleotide

-activate receptors: activate protein that binds to guanine nucleotide
–>activated G protein modifies enzyme activity
–> GTPase: activates when GTP hydrolyzed to GDP then inactivates

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11
Q

structure of GPCR; what is the receptor and the subunits?

A

receptor- integral transmembrane protein (7 pass)
-3 protein subunits; alpha, beta, gamma

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12
Q

what is an unstimulated GPCRs confirmation?

A

alpha bound to GDP and beta gamma bound to alpha

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13
Q

what is an stimulated GPCRs confirmation?

A

alpha releases GDP, replace with GTP and alpha subunit disengage from beta gamma subunits

-alpha hydrolyzes GTP to GDP and becomes inactivated again

beta gamma subunit can also sometimes activate signals

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14
Q

Gs, Gi, Gq

A

Gs- stimulate
Gi- inhibit
Gq- unique

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15
Q

Gs GPCR pathway

A
  1. ligand binds to receptor associated with Gs
  2. Gs release GDP, alpha subunit binds GTP
  3. Gs binds and activated adenylyl cyclase
    –> adenylyl cyclase enzyme converts ATP –> cAMP
  4. cAMP binds protein kinase A (PKA)
    –>binds and releases inhibitors, left active parts work
  5. PKA phosphorylates a multitude of effector proteins (transduction)
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16
Q

what enzyme does Gs GPCR use? and what does it do?

A

adenylyl cyclase

converts ATP into cAMP

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17
Q

what protein kinase is in a Gs GPCR

A

protein kinase A

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18
Q

what is Gs GPCR secondary messenger

A

cAMP

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19
Q

what happens when Gs GPCR has activated signal transduction (at end of pathway)?

A

activate signal transduction by releasing PKA inhibitors; allows Ca2+ to move down [ ] gradient from storage to cytosol

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20
Q

how to make cAMP and how to inactivate it

A

ATP –> cAMP via adenylyl cyclase

inactivate cAMP –> 5’-AMP via cyclic AMP phosphodiesterase

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21
Q

G protein mechanism of action and what is the exception

A

G protein activated –> 2nd messenger increase or decrease –> modulation of effector that responds directly to 2nd messenger (2nd messenger effector) –> 2nd messenger effector modulates activity of other effectors

exception: sometimes beta gamma subunit activates effectors on their own without using a 2nd messenger

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22
Q

Gs GPCR

-subunit
-subunit activity (impact on 2nd messengers)
-biochemical effects
-a few biologic impacts

A

-subunit: alpha

-subunit activity (impact on 2nd messengers): stimulates adenylyl cyclase –> cAMP production

-biochemical effects: cAMP activates PKA –> phosphorylation of effectors

-a few biologic impacts: glycogenolysis, thyroid hormone synthesis

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23
Q

Gi GPCR

-subunit
-subunit activity (impact on 2nd messengers)
-biochemical effects
-a few biologic impacts

A

-subunit: alpha

-subunit activity (impact on 2nd messengers): inhibits adenylyl cyclase –> decreased cAMP production

-biochemical effects: decreased PKA activation

-a few biologic impacts: inhibition of glycogenolysis, thyroid hormone synthesis etc.

-subunit: beta gamma

-subunit activity (impact on 2nd messengers): activates K+ channels (no 2nd messenger involved)

-biochemical effects: more negative cell membrane potential

-a few biologic impacts: reduction of heart rate

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24
Q

Gq GPCR

-subunit
-subunit activity (impact on 2nd messengers)
-biochemical effects
-a few biologic impacts

A

-subunit: alpha

-subunit activity (impact on 2nd messengers): activates phospholipase C –> IP3 and DAG production

-biochemical effects:
-IP3–> calcium release rom ER
-DAG–> activation of PKC

-a few biologic impacts

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25
Q

what is the differences between the GPCRs in terms of which subunits they have?

A

Gs and Gq only have alpha subunit, Gi has alpha and beta gamma

26
Q

Gq GPCR; what cleaves the secondary messengers?

A

phosholipase C

27
Q

how do calcium and calmodulin work in a Gq GPCR?

A

calcium binds calmodulin

-resting cell has no calcium in the cytosol, more in ER and extracellular space

-[ ] gradient, want to enter cytosol, increase [ ] in cytosol then bind to calmodulin = effect

-activate calmodulin with 4 Ca2+ –> bind effectors (ie. calmodulin kinases)

28
Q

what are the steps of a Gq GPCR?

A
  1. ligand bind receptor associated with Gq GPCR
  2. Gq alpha activates phospholipase C
  3. phospholipase C cleaves a membrane lipid into IP3 and diacyl glycerol
    -membrane lipid = PIP2
    -IP3 is water soluble- enters the cytosol
    -DAG is lipid soluble- stays within the cell membrane and diffuses
  4. IP3 activates Ca2+ release channel in ER (ER –> cytosol)
  5. Ca2+ and DAG activates protein kinase c (PKC)
  6. PKC (2nd messenger-activated effector) can modulate activity of other effectors… Ca2+ can also bind calmodulin
29
Q

Gi GPCR

which subunit has the effect? which channel does it open?

A

beta gamma subunit opens the K+ channel

K+ leaves the cell, makes it more negative

30
Q

example of an ion channel coupled receptor

A

Na+/K+ ATPase

31
Q

Na+/K+ ATPase

A

3 Na+ out
2 K+ in

-Na+/K+ ATPase and K+ channel cause negative inside with low cytosolic [Na+] and high [K+]
–> Na+ wants to diffuse into cell if Na+ channels open to make the membrane potential more +
-very low Ca2+ inside the cell, wants to move in

32
Q

depolarization vs hyper polarization

A

let Na+ enter through channel opening= depolarization (become more positive)

depolarization phase, the gated sodium ion channels on the neuron’s membrane suddenly open and allow sodium ions (Na+) present outside the membrane to rush into the cell. As the sodium ions quickly enter the cell, the internal charge of the nerve changes from -70 mV to -55 mV.

hyperpolarization= K+ channels let K+ leave and inside becomes more negative

Hyperpolarization is when the membrane potential becomes more negative at a particular spot on the neuron’s membrane, while depolarization is when the membrane potential becomes less negative (more positive).

-many receptors can open ion channels after they bind a ligand (1st messenger)
-i.e. calcium enters and calmodulin binds

33
Q

enzyme coupled receptors; what are the 2 possibilities for the cytosolic domain?

A

intrinsic enzyme activity (I,.e receptor tyrosine kinase)

or

direct association with an enzyme

34
Q

Gq GPCR what are the secondary messengers?

A

IP3 and DAG

35
Q

what do the Gq GPCR secondary messengers do?

A

-IP3–> calcium release rom ER

-DAG–> activation of PKC

36
Q

Gq GCPR

A

-uses Ca2+, IP3, DAG as 2nd messengers
-IP3 causes release of calcium from storage in ER
-calcium binds and activates many proteins/effectors
–> calcium binding protein is calmodulin

37
Q

what binds Ca2+ in a Gq GPCR? how many calcium need to bin it?

A

calmodulin and 4 calcium

38
Q

which membrane lipid gets cleaved into diacylglycerol DAG and IP3 in a Gq GPCR?

A

PIP2

39
Q

enzyme coupled receptors

A

transmembrane proteins with ligand-binding domain on outer surface of plasma membrane - usually 1 transmembrane domain

40
Q

what does ligand binding do to a receptor tyrosine kinase?

A

cause it to dimerize and activates tyrosine kinase within the receptor

41
Q

receptor tyrosine kinase

A

binding of ligand dimerizes the receptor and activates tyrosine kinase within the receptor
–>phosphorylation by the receptor on its own tyrosine residues activates the receptor –> further signaling

42
Q

what type of activity does a receptor tyrosine kinase have?

A

intrinsic kinase activity: i.e. receptor phosphorylates itself on specific residues of the intracellular face of the receptor

43
Q

what are some ligand examples that can bind a receptor tyrosine kinase?

A

insulin, cytokines, growth factors

44
Q

steps of receptor tyrosine kinases

A
  1. ligand binds to receptor monomers
  2. receptor dimerizes and each 1/2 phosphorylates the tyrosine residue on the other 1/2
  3. signalling proteins then bind to the phosphorylated receptor and also become activated –> signal cascade
45
Q

receptor tyrosine kinase signalling options: phospholipase C

A

same as Gq GPCR

IP3 and DAG –> PKC

46
Q

receptor tyrosine kinase signalling options: ras cascade

A
  1. ras (small intracellular G protein) sees activated RTK and activates itself via binding GTP
  2. Was activated Raf (small plasma membrane associated G protein)
    3.activated Raf –> activation of MAP kinases
    –> phoshorylate transcription factors, enzymes… many effectors
  3. Ras inactivates itself by cleaving GTP to GDP
47
Q

what is the AKT system for on a receptor tyrosine kinase

A

insulin signalling

48
Q

what is the ras-raf-MAP kinase ligand?

A

growth factors

49
Q

what happens after Ras binds Raf in an RTK

A

then you have the MAP kinases all phosphorylate

50
Q

what is the 2nd messenger in a Ras-Raf-MAP RTK?

A

no typical 2nd messenger

51
Q

receptor tyrosine kinase signalling options: PI-3 kinase - AKT system

what is the signalling for and what are the steps?

A

-insulin signaling

  1. RTK activated –> activates phosphoinositide-3-kinase (PI3K)
  2. PI3K attaches another phosphate to PIP2 (membrane lipid) –> PIP3
  3. PIP3 accumulates and forms “lipid” rafts in the membrane
    –> PIP3 is a 2nd messenger
  4. Akt and PDK1 (both kinases in the cytosol) accumulate and cluster together at the site of the PIP3 rafts
    –> PDK1 becomes activated by PIP3
  5. when PDK1 is activated, it activates Akt by phosphorylating it
  6. Akt is the effector -many intracellular targets (also regulated on/off by others)
52
Q

what is the second messenger in RTK PI3 kinase and AKT system? and what does it form

A

PIP3 is second messenger and forms lipid rafts (for PDK1 and Akt)

53
Q

PI3 kinase role in cell signalling - what are its products?

A

converts many phospholipids into PIP3

54
Q

what converts PIP2 to IP3 and DAG in Gq activation

A

PLC (phosholipase C)

55
Q

what is the effector molecule in the PI3K Akt system?

A

Akt

56
Q

what does nitric oxide do to smooth muscles

A

relaxes them

57
Q

how is nitric oxide produced

A

by nitric oxide synthase (NOS) on L-arginine

because of increase in cytosolic calcium concentration activate NOS

58
Q

what role can nitric oxide play in cell signalling

A

act as 2nd messenger

59
Q

nitric oxide

A

-key mediator that relaxes smooth muscle in a wide variety of blood vessels and visceral organs
-small hydorphobic gas –> diffuses quickly, can effect many cells
-produced enzymatically by the action of nitric oxide synthase (NOs) on L-arginine
- increased cytosolic calcium can also activate NOs
-nitric oxide rapidly degrades (reacts with oxygen and water)

-2nd messenger than can diffuse; only local effects bc quickly degraded free radical

60
Q

nitric oxide mediated signalling

A
  1. cytosolic calcium increases
  2. intracellular calcium activates nitric oxide synthase
  3. nitric oxide synthase produces nitric oxide from L-arginine
  4. nitric oxide binds and activates guanylyl cyclase (GC) –> production of cGMP (secondary messenger) from GTP
  5. elevations of cytosolic cGMP activated a protein kinase (usually PKG)
    -changes in cellular activity due to PKG activity
    -disengage myosin from actin in smooth muscle= relaxation
61
Q

nitric oxide; what does it use for energy and what 2nd messenger is produced

A

GTP –> cGMP

BMS100 test 1 (24 decks)

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