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Biology Exam 2 > Cell Communication > Flashcards

Cell Communication Flashcards

1
Q

define signal transduction

A

cell to cell communication

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2
Q

in general how does signal transduction work?

A
  1. extracell signal binds to receptor protein on memb.
  2. binding causes an intracell signal to be released
  3. intracell signal activates effector proteins
  4. effector proteins cause the outcome
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3
Q

what are 3 outcomes of effector proteins?

A
  1. altered metabolism
  2. altered gene expression
  3. altered cell shape or mvt
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4
Q

more specific signal transduction definition

A

extracellular signaling molecules bind to specific receptors in target cells to initiate a chain of events

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5
Q

external signals induce 2 major types of responses

A
  1. fast response

2. slow response

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6
Q

fast response

A

change in activity or function of enzymes or proteins in cell

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7
Q

slow response

A

change in amounts of proteins by change in gene expression

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8
Q

signal transduction process

A
  1. ligand
  2. high affinity receptors
  3. intracell signal proteins
  4. effector proteins
  5. outcome
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9
Q

list the types of signaling

A
  1. endocrine
  2. paracrine
  3. synaptic
  4. autocrine
  5. direct cell
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10
Q

long distance signaling

A

endocrine signaling

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11
Q

endocrine signaling

A

long distance, long half-life

signal enters blood stream and travels to reach it’s target

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12
Q

local signaling

A

paracrine signaling
or
synaptic signaling

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13
Q

paracrine signaling

A

local, not freely diffusible

affects the nearby cells

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14
Q

synaptic signaling

A

acts locally

affects nearby axons/dendrites using neurotransmitters

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15
Q

signals to the cells that released the signal

A

autocrine signaling

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16
Q

autocrine signaling

A

cell releases a signal to affect itself and/or cells of same type nearby

ex. growth factors

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17
Q

immune cell signaling

A

direct cell signaling

ex. Ag presenting to T cells

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18
Q

each cell interprets all the signals it gets to determine what to do…..

A

survive
die
divide
differentiate

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19
Q

signals

A

or ligands
typically secreted via exocytosis

signal types decides where signal goes

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20
Q

receptors

A

bind specifically to signal molecules w/ high affinity

because signals are produced in low levels

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21
Q

effectors

A

the targets of receptors intracell

alter cell activity to create 2nd messengers

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22
Q

main types of ligands

A
  1. small lipophilic - hormones

2. water soluble molecules or hydrophilic

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23
Q

general types of receptors

A
  1. cell surface receptors

2. intracellular receptors

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24
Q

describe intracellular receptors

A

steroid receptors - can be present in cytosol since the signal can easily pass thru the bilayer

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25
Q

7 transmembrane receptors

A

or G-protein coupled receptors

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26
Q

describe the structure of G-protein coupled receptors

A

have 3 domains

  1. extracell - binds ligands
  2. transmemb. - anchors
  3. cytoplasmic domain - associates w/ G protein
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27
Q

G-proteins

A

heterotrimeric proteins composed of 3 subunits (a b g)

GTP or GDP

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28
Q

describe the steps of G-protein relaying signals

A
  1. ligand binds receptor
  2. conformational change occurs in receptor
  3. receptor binds to G
  4. receptor acts as GEF
  5. GDP exchanged for GTP
  6. Ga is now active an binds to effector to activate it
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29
Q

adenylyl cyclase

A

an effector protein that catalyzes formation of cAMP

which is the 2nd messenger that can cause a biological response

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30
Q

reset of G-protein system

A

hydrolysis of GTP bound to Ga occurs

Ga inactivated and recycled/sent back to starting point

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31
Q

what is the significance of a G-protein coupled receptor acting as a GEF?

A

guanine exchange factor

it exchanges the GDP for a GTP which causes Ga to become activated

it exchanges, not phosphorylating

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32
Q

Gas

A

stimulating Ga type

stims adenylyl cyclase

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33
Q

Gai

A

inhibiting Ga type

inhibits adenylyl cyclase

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34
Q

cAMP

A

a 2nd messenger

activates a protein kinase called PKA

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35
Q

PKA

A

a protein kinase activated by cAMP

can phosphorylate proteins to either activate or inactivate them

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36
Q

PKA structure

A

inactive form - has 4 subunits
2 catalytic, 2 regulatory

active form - the 2 catalytic units released as separate entities

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37
Q

binding of cAMP to PKA

A

2 cAMP binds to each regulatory subunit (so 4 total)

causes the 2 catalytic units to be released from the regulatory units

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38
Q

how does phosphorylation change a proteins function?

A

it changes the shape of the protein

and protein shape determines it’s function

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39
Q

what is meant by amplification of signaling?

A

a single ligand receptor event can activate multiple effector protein to generate hundreds of 2nd messengers which effect 1000’s of proteins

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40
Q

what is desensitization of a signal?

A

ability to turn off or reject the signal

important for preventing cancer cell growth

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41
Q

list the 5 ways to stop a signal in a signal transduction pathway

A
  1. receptor sequestration
  2. receptor destruction
  3. hormone level drop
  4. signal removal
  5. GRKs
42
Q

receptor sequestration

A

invagination of the membrane to take the receptor off the cell surface

thus the cell cannot receive signals

43
Q

receptor destruction

A

cell invaginates the signal
the endosome combines w/ lysosomes
receptor protein destroyed

thus the cell cannot receive signals

44
Q

dropage of hormone levels

A

decreases adenylyl cyclase activity
which decreases cAMP
which decreases PKA

thus decreases/stopping the signal transduction pathway

45
Q

removal of signaling molecules

A

phosphodiesterase will remove cAMP

thus no 2nd messenger - no outcome

46
Q

define GRKs

A

G-protein receptor kinases

capable of phosphorylating G-protein coupled receptors

47
Q

GRK effects

A
  1. phosphorylates a receptor
  2. now the protein arrestin will bind
  3. results: receptor cannot act as GEF

thus signal pathway stopped since Ga cannot be activated

48
Q

arrestin

A
  • -a protein that can bind to a G receptor after GRK binds
  • -binds to the 3rd intracell loop
  • -which prevents Ga from interacting w/ loop 3

resulting in Ga not being converted to Ga-GTP

49
Q

PKA: addition of 2 negative charges can change ….. ?

A

the conformation of the protein thus changing it’s function

50
Q

GPCR

A

G-protein coupled receptor

51
Q

other G-protein variants

A

Gao

Gaq

52
Q

variant G-protein GPCR pathway: signal to 2nd messengers

A
  1. ligand binds
  2. GPCR binds Gao/q
  3. GPCR acts as GEF
  4. active Ga binds to phospholipase C
  5. phospholipase C cleaves PIP2
  6. produces IP3 and DAG
53
Q

IP3

A

produced when phospholipase C cleaves PIP2

binds to IP3 ligand gated channels on ER to trigger opening to release Ca into cytosol

54
Q

DAG

A

produced when phospholipase C cleaves PIP2

works w/ Ca to activate PKC

55
Q

PKC

A

protein kinase C

Ca and DAG both bind to and activate PKC

PKC undergoes conformational change and can now phosphorylate a variety of substrates

56
Q

2 roles of Ca discussed in cell signaling

A
  1. working w/ DAG to activate PKC

2. binding to calmodulin to activate it

57
Q

calmodulin

A

Ca binds to activate it

can bind to different cellular proteins to activate their functions

58
Q

calmodulin example

A

binds to CaM kinase II

which can then phosphorylate transcription factors to induce transcription

59
Q

list the other 3 types of signal transduction

A
  1. tyrosine kinases
  2. jak-stat receptors
  3. serine/threonine kinases
60
Q

RTK purpose

A

play important role in signal transduction

are used in response to growth factors

growth factor = ligand/signal

61
Q

RTK domains

A
  1. extracellular domain
  2. transmembrane domain
  3. cytoplasmic/enzymatic domain
62
Q

RTK extracellular domain

A

ligand binding

ligand for R7 = Boss

63
Q

RTK ligand binding

A
  • -causes conformational change
  • –2 receptors dimerize
  • —autophosphorylation occurs
64
Q

autophosphorylation

A

occurs in ligand bound RTK receptors

causes receptors to act as scaffolding/docking sites to recruit other proteins to plasmalemma

65
Q

RTK transmembrane domain

A

anchors the receptor in the plasmalemma

66
Q

RTK cytoplasmic domain

A
  • -has a tyrosine kinase domain that acts as enzymatic domain
  • -where the signal transmits thru
67
Q

what does RTK signal transmittance thru ______ result in

A

thru tyrosine kinase domain to phosphorylate protein attached

68
Q

RTK pathway

A
  1. growth factor binds
  2. RTK dimerize, autophosphorylate
  3. RTK binds to SH2 of Grb2
  4. SH3 of Grb2 binds to SOS via prolines
  5. SOS acts as GEF to Ras
  6. Ras-GTP binds to Raf
  7. active Raf initiates Map kinase pathway
69
Q

what does the Map kinase pathway lead to?

A

changes in gene expression

to result in cell proliferation

70
Q

what are the more direct routes for impacting transcription?

A
  1. jak-stat

2. smad

71
Q

what initiates the MAP kinase cascade

A

activate Raf via the binding of Ras

72
Q

MAP kinase cascade is propagates the signal downstream by using ?

A

ATP to phosphorylate the next substrate

73
Q

list the Map kinase cascade

A
  1. Raf activates Mek
  2. Mek activates Erk
  3. Erk enters nucleus

resulting in changes in gene transcription to cause cell proliferation

74
Q

map kinase kinase kinase

A

raf

75
Q

map kinase kinase

A

mek

76
Q

map kinase

A

erk

77
Q

MAP

A

mitogen activated protein kinase

results in cell proliferation

78
Q

JAK-STAT pathway

A
  1. ligand binds receptor
  2. receptors dimerize
  3. 2 jaks bind
  4. jaks phosphorylate each other and receptors
  5. receptor binds 2 stats and phosphorylate them
  6. stats separate, dimerize, enter nucleus, bind to DNA
  7. causing transcription of target genes
79
Q

janus kinases

A

JAK

80
Q

many signaling molecules are ________ that can mutate into oncogenes and cause _____ .

A

protooncogenes and cause cancer

81
Q

STAT

A

signal transducer and activators of transcription factors

82
Q

example of jak-stat pathway

A

kidneys produce erythropoietin which employs the jak-stat to initiate signaling to result in increased production of RBCs

83
Q

R-Smad =

A

receptor specific smad

84
Q

Co-Smad =

A

common smad

85
Q

R-smad forms a complex w/ ?

A

co-smad

86
Q

how is the receptor activated in the smad pathway?

A

via phosphorylation

87
Q

Serine/Threonine pathway

A

= smad path

  1. receptor activated
  2. receptor binds to r-smad and phosphorylates it
  3. active r-smad dissociates and binds to co-smad to create complex
  4. complex moves into nucleus
  5. impacts target genes for transcription
88
Q

what the example of the smad pathway used in class?

A

hereditary hemochromatosis

iron metabolism - expression of hepcidin

89
Q

hepcidin

A

protein made in liver that regulates the uptake of Fe

binds to Ferroportin in intestinal cells to cause invagination and proteolysis of ferroportin

90
Q

high hepcidin levels

A

= no fe uptake

91
Q

low hepcidin levels

A

= fe uptake via Ferroportin in intestines

92
Q

iron pathway: food to blood stream

A

enters intestinal cells via DMT1 on apical surface

exits cell into blood via Ferroportin on basal domain

93
Q

hereditary hemochromatosis

A

–genetic disease of uncontrollable iron absorption, leading to fe overload and organ failure

—due to mutations in hfe gene – also called C282Y mutation

94
Q

significance of hfe gene

A

hfe binds to transferrin receptors

if mutated it cannot turn on hepcidin expression

thus no control of ferroportin

95
Q

hfe works thru a ___ pathway

A

smad

96
Q

a mutated hfe cannot signal _____ to do ?

A

tfR2

to start smad path to express hepcidin

97
Q

point mutation in codon 12

A

results in Gly replaced w/ Val

this constitutively activates Ras

which is always found in human cancer

98
Q

how is protein kinase C activated?

A
  1. signal binds GPCR
  2. GPCR acts as GEF to Gao/q
  3. activates phospholipase C
  4. it cleaves ip2
  5. producing ip3 and dag
  6. ip3 causes er to release Ca
  7. dag + Ca bind to PKC to activate it
99
Q

describe how a mutation in hfe causes a signal transduction problem? and what does it lead to ?

A

if hfe is mutated it cannot bind to tfr2 to activate the smad pathway that leads to expression of hepcidin. if hepcidin is not present to regulate Ferroportin activity, this leads to iron overloading-uncontrollable absorption of iron.

leading hereditary hemochromatosis

100
Q

hfe binds to ?

A

TfR2

Biology Exam 2 (9 decks)

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