BIO230 > Cell communication > Flashcards

Cell communication Flashcards

(54 cards)

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1
Q

examples of unicellular communication

A

quorum sensing in bacteria
- release and response to chemical signals

mating in budding yeast
- signaling b/w yeast cells prepares them to mate

aggregation of ameboid cells
- signalling between dictyostelium cells draws them together

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2
Q

two main ways of receiving a signal

A
  1. cell-surface receptors
    - for hydrophilic signal molecules
  2. intracellular receptors
    - for hydrophobic molecules
    - has to pass through the membrane of the target cell
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3
Q

contact-dependent signaling

A

signals retained on the cell surface

- faster

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4
Q

pararcrine signaling

A
  • signals released from the cell but act locally

restricted by

  • internalization by neighbouring cells
  • signal instability or destruction by extracellular enzymes
  • binding to extracellular matrix molecules
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5
Q

synaptic signaling

A

neuron reaches a long distance then communicates

  • neurons extend acons to contact distant target cells
  • the released signaling molecules act locally at target
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6
Q

endocrine signaling

A

endocrine cells secrete hormones into the bloodstream for long-range distribution
- diffusion out of blood into target cell

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7
Q

signal transduction

A

the conversion of extracellular signals into intracellular signals

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8
Q

effector

A

downstream molecule in a signal transduction pathway

- upstream molecules have their effects on them

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9
Q

signal transduction pathway

A

extracellular signal molecule –> receptor protein –> intracellular signaling proteins –> effector proteins

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10
Q

effector proteins (3)

A
  • metabolic enzyme
  • gene regulatory protein
  • cytoskeletal protein
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11
Q

second messengers

A

small intracellular signaling molecules

  • made in large numbers and diffuse through cytoplasm or plasma membrane
  • bind and alter effector molecules
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12
Q

signaling by phsophorylation

A

for serine/threonine kinases and tyrosine kinases

  • phosphorylation, powered by ATP hydrolysis turns ON
  • dephosphorylation turns OFF
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13
Q

signaling by GTP binidng

A
  • large trimeric and small monomeric type proteins
  • have low GTPase activity
  • GTP binding (GDP –> GTP) turns ON
  • GTP hydrolysis (regulated by GAP) turns OFF
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14
Q

GAPs

A

GTPase activating proteins

- increase the GTP hydrolysis

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15
Q

GEFs

A

Guanine nucleotide exchange factors

- promote the exchange of GDP for GTP

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16
Q

examples of signaling pathways

A
  • SH2 and PTB domains bind phosphotyrosine containing sequences
  • PH domains bind phosphoinositides
  • SH3 domains bind proline-rich sequences
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17
Q

synaptic signaling specificity

A

neurons make connections with specific target cells

  • all based on location
  • the same neurotransmitter can be used
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18
Q

endocrine signaling specificity

A

different molecules are released and target cells express specific receptors to respond to specific molecules

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19
Q

what prevents an upstream signal from activating all of the pathways?

A

the formation of local complexes helps insulate pathways from each other
- must be activated by an activated receptor

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20
Q

coincidence detectors

A

only activate downstream signals when two upstream signals are both detected

  • pathway is activated
  • protein kinase phosphorylates y, each specific to one side of y
  • downstream signals are only activated if y is phosphorylated on both sides
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21
Q

what determines the response speed to a signal

A

it varies depending on the cellular machinery involved

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22
Q

effects of positive feedback

Study These Flashcards
A
  • enhancing the response
  • strong enough feedback can be self-sustaining
  • bistable systems can stably exist in on or off states
23
Q

effects of negative feedback

Study These Flashcards
A
  • if it occurs quickly, signal is suppressed
  • allows cells to respond to changes in upstream signals and a wider range of signal strengths
  • if it occurs slowly, the system can oscillate
24
Q

NO as a signaling molecule

Study These Flashcards
A
  • made by deamination of arginine by NO synthases
  • acts locally
  • affects smooth muscle and other target cells
  • rapid diffusion of NO can cause relaxation of smooth muscle cells
25
steroid hormones
- made from cholesterol | - affect sexual characteristics and metabolism
26
thyroid hormones
- made from tyrosine | - increase metabolic rate
27
retinoids
- made from vitamin A | - regulate development
28
vitamin D
affects metabolism
29
nuclear receptor superfamily
- contain binding sites for a small hydrophobic molecule as well as for DNA - 48 in the human genome - more than half only identified based on sequence analysis
30
ligand binding and conformation
- binding to a ligand induces conformation and release of inhibitors - DNA binding and downstream transcription promoted
31
ion channel properties
- narrow selective pores - open and close rapidly - transport is passive (based on electrochemical gradients and ion diffusion)
32
different types of ion channels
- voltage gated - ligand gated (intracellular and extracellular) - mechanically gated
33
ion channel functions
- electrical excitability of muscle cells - electrical signaling in the nervous system - leaf closure responses in plants - signal the single-celled paramecium to reverse its movement upon collision
34
nerve impulses
- synaptic vesicles release neurotransmitters through exocytosis - these bind to and open ligand gated channels - channels allow ion passage into the target cell to create another nerve impulse or a different effect
35
GPCR
G-protein coupled receptors - 7 pass transmembrane proteins - activated by proteins, small molecules, and light - more than 700 in humans
36
GPCR signaling
- signaling done via a membrane associated trimeric GTP-binding protein - functions as a GEF to change GDP --> GTP on the alpha subunit - a subunit goes through a conformational change and induces release of other subunits - subunits bind to downstream effectors - turned off by a regulator of G protein signaling (RGS) which acts as a GAP
37
cAMP and its pathway
- synthesized from ATP by adenylyl cyclase - destroyed by cAMP phosphodiesterase - signal is transduced by increasing adenylyl cyclase activity above a constant background of phosphodiesterase activity - cAMP activates PKA which phosphorylates CREB to activate transcription - release of separate molecules forms a tetramer
38
GPCR signaling via calcium
- signal molecule activates GPCR - Gq is acivated by GTP - activated phospholipase C-b causes release of IP3 - diacylglycerol is left behind on the membrane - IP3 diffuses through cytoplasm amd activate IP3 gates - Ca2+ released and activate PKC
39
enzyme-coupled receptors
- receptor tyrosine kinases - receptor serine/threonine kinases - histidine-kinase-associated receptors
40
signaling by receptor tyrosine kinase
- ligand binding dimerizes the receptor - kinase domains brought together and phosphorylate each other at the same time - phosphorylation of kinase domains enhances activity - phosphorylation of other regions creates docking sites to assemble a signaling complex - recruition of proteins that mediate downstream signaling
41
what happens when a defective kinase domain is expressed with a normal receptor?
the cell has reduced response to the signal
42
drosophila and tyrosine kinase
- omnatidia compose of photoreceptor and support cells - arise from epithelial sheet through sequential differentiation of the photoreceptor cells - R7 is last to differentiate and needed to detect uV light
43
Sevenless mutant
- helped discover what was necessary for R7 differentiation | - normal Sev protein shown to be a receptor tyrosine kinase in R7 cells
44
Bride-of-sevenless (Boss)
ligand for Sev expressed on R8 cells
45
Drk and Son-of-Sevenless (Sos)
- Drk links Sev to Sos | - Sos is a GEF for Ras
46
Ras
a molecular switch downstream of receptor tyrosine kinase - monomeric GTPase - attached to cytoplasmic face of the plasma membrane by a lipid anchor - activated by Ras-GEF and inactivated by Ras-GAP - leads to cell proliferation
47
Ras and MAP kinase module
- Ras activated MAPKKK - phosphorylates MAPKK - phosphorylates MAPK - phosphorylates effecor proteins - changes in protein activity and gene expression
48
receptor serine/threonine kinases
- largest class, 6 major families in plants - Clv1/Clv2 signals stimulate the development of stems, leaves, and flowers - ser-thr kinase phosphorylates itself and its neighbour - protein phosphatase can turn off the signal through dephosphorylation
49
histidine-kinase-associated receptors
- activate a two component signaling pathway - used by bacteria, yeast, and plants - repellent binds to receptor activating CheW - CheA is activated, phosphorylates itself and transfers the phosphate onto CheY
50
lateral inhibition by notch signaling
- top cell inhibits notch activation - both start off with delta and prevent each other's delta expression - each cell inhibits its neighbour - cell with active delta specializes
51
activating a notch cell
- delta binds to big fragment - top cell has to endocytose the large one - mediated by clathrin - rest of notch is activated down
52
notch cell pathway
- cleavage at site 1 - transport to plasma membrane - binding to delta, endocytosis of delta-notch-fragment complex and cleavage at site 2 - cleavage at site 3 - notch tail migrates to nucleus - protein complex containing notch tail activates gene transcription - leads to inhibition of delta expression and cell specialization
53
Sonic hedgehog
- source of morphogen - Shh spreads and the gradient controls formation of distinct digits - without it, CI is sequestered in the cytoplasm by a microtubule associated complex - promotes proteolysis of Ci to a transcriptional repressor
54
Patched
binding with Hedgehog allows smoothened to transfer to the plasma membrane and release Ci from its inhibitory complex - difference determined by presence or absence of a cut
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