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BIOL 3302 > cell signaling > Flashcards

cell signaling Flashcards

1
Q

what is signal transduction?

A

process where cells communicate with the external and internal environment, with neighboring cells, and with oneself

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2
Q

why do cells need to communicate with each other?

A

to live in a harmonious way by coordinating actions with each other

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3
Q

what can defects in cell signaling result in?

A

diseases such as insulin signaling defect which causes diabetes mellitus

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4
Q

what are the basic components of a signaling pathway?

A
  • signal molecule or ligand (can be extracellular or intracellular)
  • receptor protein on the plasma membrane or in the cytoplasm
  • intracellular signaling proteins
  • effector proteins
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5
Q

define endocrine signaling

A
  • extracellular
  • happens at a great distance
  • examples include hormone secretion and insulin
  • falls in secreted ligands category
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6
Q

define paracrine signaling

A
  • extracellular
  • ligands secreted into extracellular space and travel between adjacent cells
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7
Q

define autocrine signaling

A
  • extracellular
  • self signaling occurring on the same cell
  • example would be growth factor secretion that stimulates the proliferation of the same cell
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8
Q

define plasma-membrane-attached protein signaling

A
  • is a type of extracellular signaling
  • can be classified as paracrine (between adjacent cells)
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9
Q

what is the Notch Delta pathway?

A
  • example of paracrine signaling
  • occurs between adjacent cells
  • delta is the ligand and notch is the receptor
  • as delta binds to notch, notch is cleaved and the tail migrates to the nucleus to induce gene transcription
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10
Q

what are the two types of receptors?

A
  • cell surface or intracellular receptors
  • cell surface bind to surface of cell and usually have a hydrophilic signal molecule that cannot cross the membrane
  • intracellular receptors are present in the cytoplasm or nucleus
  • intracellular receptors have hydrophobic signal molecule that can cross the plasma membrane
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11
Q

_______ can be in the cytoplasm and once bound can undergo a conformational change to move to the nucleus

A

intracellular receptors

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12
Q

what is an example of an intracellular signal molecule (ligand)?

A

steroid and thyroid hormones

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13
Q

describe the basic steroid hormone pathway

A

hormone passes through membrane and binds with receptor protein inducing a conformational change that activates the receptor protein. activated receptor-hormone complex moves into the nucleus where it binds to the regulatory region of the target gene to activate transcription.

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14
Q

what is the minimal pathway?

A
  • signaling pathway composed of a signal molecule and a receptor-effector protein
  • the receptor functions as its own effector
  • examples include the steroid hormone pathway and the notch-delta pathway
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15
Q

describe the three types of effector proteins and their effect

A
  • metabolic enzyme: can lead to altered metabolism
  • gene regulatory protein: can lead to altered gene expression
  • cytoskeletal protein: can lead to altered cell shape or movement (migration)
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16
Q

what would result in a FAST response rate?

A

change in protein function (example: protein phosphorylation)

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17
Q

what would result in a SLOW response rate?

A

producing new proteins (example: gene transcription)

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18
Q

what is the primary function of the signal transduction pathway?

A

to relay the signal to the cell

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19
Q

what are some additional functions of the ST pathway?

A
  • to transduce and amplify signal
  • to integrate signals from various signaling pathways
  • to distribute the signal to more than one effector protein
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20
Q

describe signal amplification and the benefit involved in this function

A
  • signal amplification involves the relaying of a signal from 1 molecule to 100 molecules to 10,000 molecules (a cascade)
  • the more components you have the more control you can have over the pathway
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21
Q

describe what switch proteins are

A
  • proteins that can switch between active and inactive form
  • function as signaling proteins
  • usually involve a cascade that turns effector on and leads to cellular response
  • classified as either phosphorylated proteins or GTP-binding proteins
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22
Q

describe second messengers

A
  • NOT proteins but small molecules that aid in signaling
  • examples include calcium or lipid molecules
  • activated by the activation of an enzyme which releases the second messenger
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23
Q

how are phosphorylated proteins regulated between active and inactive state?

A
  • addition of phosphate due to kinase switches protein from inactive to active
  • removal of phosphate due to phosphatase switches protein from active to inactive
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24
Q

what amino acids are useful in kinase activity (protein phosphorylation)

A

serine, threonine and tyrosine due to the hydroxyl group on side chain

25
Q

GTP-binding proteins are an example of __________ regulation

A

non covalent

26
Q

what are the two types of GTP-binding proteins?

A

monomeric GTPases and trimeric GTP-binding proteins (aka G proteins)

27
Q

how are GTP-binding proteins regulated between active and inactive state?

A
  • GTP binding (removal of GDP) switches from inactive to active
  • GDP binding (removal of GTP) switches from active to inactive
28
Q

describe the role of GAP and GEF in the activity cycle of GTP-binding proteins

A
  • GAP allows for faster exchange of GTP to GDP (faster switch from active to inactive state)
  • GEF exchanges GDP with GTP for faster activation
29
Q

how can mutations in GEF and GAP influence the activity cycle?

A
  • a mutation in GAP can cause GTP to be bound all the time so the protein is always active
  • a mutation in GEF means the protein is always inactive
30
Q

trimeric GTP-binding proteins use __________ instead of GEF

A

GPCR

31
Q

what is Ras?

A
  • it is a monomeric GTPase
  • exists as a single protein
  • activated by receptor tyrosine kinase
  • mutant form can cause permanent GTP bound conformation leading to proliferation and cancer
32
Q

Ras is especially activated in pathways that stimulate _____________ and ____________

A

cell division, cell differentiation

33
Q

what is the first messenger in ST pathway?

A

the signal molecule (ligand)

34
Q

what is the purpose of second messengers?

A

they diffuse to act on intracellular signaling proteins after activation by an enzyme

35
Q

what are some examples of second messengers?

A
  • cAMP
  • calcium
  • cGMP
  • diacylglycerol
  • IP3
  • PIP3
36
Q

______ is a cAMP phosphodiesterase inhibitor

A

caffeine

37
Q

______ is a cGMP phosphodiesterase inhibitor

A

viagra (sildenafil citrate)

38
Q

describe the pathway involving IP3 and DAG

A
  • PLC is activated
  • causes the release of IP3 and DAG through cleavage of phospholipid into two
  • DAG activates protein kinase C
  • addition of phosphate to PIP2 forms PIP3
  • IP3 prompts release of calcium from ER
  • calcium results in conformational change of calmodulin
  • calmodulin activation prompts signal response
39
Q

how can signal transduction be terminated?

A
  • receptor down regulation which takes away the ligand
  • second messenger can be degraded
  • phosphatases can remove P to turn it off
  • negative feedback regulation can turn off production
40
Q

what are g protein coupled receptors (GPCRs)?

A
  • largest family of cell-surface receptors
  • they mediate responses to a wide variety of signal molecules
  • examples: hormones, neurotransmitters, small peptides, amino acid derivatives and fatty acid derivatives
41
Q

describe the structure of GPCRs

A

they are coupled to a heterotrimeric (alpha, beta, and gamma) G protein and span the plasma membrane 7 times. the alpha unit is the GTP binding protein.

42
Q

describe the process of activation in skeletal muscle cells

A
  • GPCR is activated
  • alpha subunit acts as switch protein changing ATP to cAMP
  • cAMP activates PKA by inducing a catalytic change (4 cAMP molecules needed)
  • active PKA induces phosphorylation of active phosphorylase kinase
  • active phosphorylase kinase activates glycogen phosphorylase which leads to glycogen breakdown
43
Q

what is the difference between Gs and Gi?

A
  • Gs is a stimulatory protein that once activated separates from the beta and gamma subunits to stimulate enzyme activity
  • Gi is an inhibitory protein that binds to the enzyme and inhibits enzyme activity
44
Q

what is the end goal of liver cell activation?

A

active PKA leads to phosphorylation of glycogen phosphorylase and phosphorylase kinase

45
Q

what is the end goal of fat cell activation?

A

active PKA leads to phosphorylation of phospholipase which results in breakdown of phospholipids

46
Q

describe receptor associated tyrosine kinase signaling

A
  • cytokine ligand binds
  • binding induces dimerization of receptors which are bound to JAK (kinase)
  • dimerization converts inactive JAK to active JAK (phosphorylation)
  • active JAK phosphorylates STAT
  • phosphorylated STAT dimerizes and moves to nucleus to activate transcription
47
Q

what is the importance of an SH2 domain in receptor associated tyrosine kinase signaling?

A

the SH2 domain helps bind to phosphotyrosine residues and induces a conformational change to allow for phosphorylation by JAK and dimerization

48
Q

describe the two mechanisms for terminating cytokine signal transduction

A
  • short-term: JAK2 deactivation by SHP1 phosphatase causing dephosphorylation (of JAK2 moving to inactive state)
  • long-term: signal blocking and protein degradation by SOCS proteins that recruit E3 ubiquitin ligase which induces degradation of JAK2 and receptor
49
Q

describe RTK activation

A
  • ligand (ex: EGFR, FGF) binds to ligand binding site
  • binding causes dimerization and activation of protein tyrosine kinase
  • cross-phosphorylation of additional tyrosine residues
  • GRB2 binds to RTK complex (GRB2 has a SH2 domain)
  • GRB2 recruits Sos protein which then activates Ras to transmit signal
50
Q

define the Ras activation pathway

A
  • activated RTK binds to adaptor protein (GRB2)
  • GRB2 recruits and binds to Ras-GEF (Sos protein)
  • Sos activates Ras by switching GDP to GTP
  • activated Ras activates MAP3K
  • MAP3K phosphorylates and activates MAP2K
  • MAP2K phosphorylates and activates MAPK
  • MAPK then goes on to activate other proteins to result in transcriptional induction
51
Q

explain the difference between MAPK direct and indirect phosphorylation

A

MAPK can directly phosphorylate TCF to result in transcription or it can activate p90rsk that can then phosphorylate SRF which activates TCF and leads to transcription

52
Q

describe TGFbeta signaling

A
  • ligand (TGFbeta) can bind to receptor III then transfer to receptor II or ligand can bind directly to receptor II
  • once bound to receptor II, receptor I is bound inducing serine-threonine kinase activity
  • receptor complex phosphorylates Smad3
  • Smad activation causes Smad3 and Smad4 to dimerize
  • dimerization leads to transcription activation
53
Q

explain hedgehog signaling

A
  • ligand (hedgehod) binds to Ptc receptor
  • binding induces movement of Smo to plasma membrane
  • movement of Smo dissociates the protein complex holding Ci (SUFU still bound to protect Ci)
  • Ci is free to move into nucleus and induce transcription
54
Q

what happens under (-) Hh signaling?

A
  • hedgehog is not bound to Ptc receptor
  • this actively induces endocytosis of Smo
  • protein complex holding Ci remains intact
  • Ci75 moves into nucleus and inhibits transcription
55
Q

explain (+) Wnt signaling

A
  • Wnt ligand binds to receptor Frizzled and LRP co-receptor
  • binding triggers GSK3 and CK1 to phosphorylate LRP
  • axin binds to phosphorylated LRP causes disruption of complex holding beta-catenin
  • free beta-catenin can move into nucleus and induce transcription
56
Q

what occurs in the absence of Wnt?

A
  • beta-catenin is bound in complex and headed for proteasomal degradation
  • Groucho binds to TCF in nucleus and inhibits transcription
57
Q

hyperactive _____ signaling can lead to the progression of cancers, in particular human ______ cancer

A

Wnt, colon

58
Q

explain Notch signaling

A
  • Notch binds to Delta on an adjacent cell
  • Delta and release Notch extracellular domain are endocytosed together by signaling cell
  • nicastrin subunit binds to Notch stump left on responding cell
  • presenilin 1 protease catalyzes cleavage to release the Notch stump
  • Notch stump moves to nucleus to activate transcription factors

BIOL 3302 (5 decks)

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