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PHGY 170 > Module 4 > Flashcards

Module 4 Flashcards

1
Q

how is cell communication achieved

A

release of substances from a cell that then travel to another cell and cause it to change its function

done though a signal that then must be relayed into the cell and trigger a cascade of events

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2
Q

cellular communication interrelation elements

A
  • extracellular communication
  • intracellular communication
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3
Q

what is extracellular communication

A
  • communication that occurs when a signal is received from outside the cell itself
  • communicate at variable distances and posses multiple strategies to communicate
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4
Q

what is intracellular communication

A

cells collect information from multiple sources, synthesize information then make decisions on how to respond to the information

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5
Q

what do cells in direct contact use to communicate

A

gap junctions

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6
Q

what do cells not touching use to communicate

A

four different types of secretion:
- autocrine secretion
- paracrine secretion
- endocrine secretion
- neurotransmitters

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7
Q

what are gap junctions made up of

A

connexons which dock together to form channels from one cell to another

allows chemical signals to move directly between cells

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8
Q

what can pass through gap junctions

A

only small particles such as ions and small signalling molecules can pass, larger molecules (proteins, carbohydrates) cant.

excitable cells (cardiac muscle cells) can pass electrical signals

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9
Q

gap junctions reglulation

A

dont allow free exchange of signals. highly regulated and open and close when appropriate (self defence mechanism from neighbouring cells)

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10
Q

autocrine secretion

A

(SAME) substances are released by a cell and have an effect on the same cell

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11
Q

paracrine secretion

A

(NEARBY) substances are released by a cell and have an effect on nearby cells

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12
Q

endocrine secretion

A

(DISTANT) substances are released by a cell and have an effect on distant cells

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13
Q

neurotransmitter secretion

A

substances are released by a nerve terminal into the synapse

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14
Q

autocrine, paracrine and endocrine secretion

A

all the same but vary in distance. substances diffuse through extracellular spaces or within the bloodstream to reach their target where they interact with a receptor to have an effect

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15
Q

how does neurotransmitter secretion occur

A

occur where a nerve cell axon terminates on a target cell

when an excitatory signal comes down the axon to the synapse neurotransmitters are released into the synapse

bind to a receptor on target cell, degrade by enzymes in the synapse or taken back up by nerve cells

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16
Q

what is required for secretion to have an effect

A

interaction with a receptor is required to initiate intracellular signalling cascades that produce specific responses

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17
Q

general process of intracellular communication

A

external stimuli (secretion) interacts with sensors on plasma membrane which triggers events within the cell (information processing), once the cell knows what the signal is produces a response to the signal through effector

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18
Q

what are the components of a signalling pathway (intracellular communication)

A
  • signal (membrane permeable or impermeable)
  • receptor (interact with signal)
  • signalling proteins (help conduct signal intracellularly)
  • second messengers (non protein molecules that help conduct signal intracellularly
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19
Q

process of the signalling pathway

A
  • membrane permeable signal binds to receptor proteins in the cytosol / impermeable binds to transmembrane cell surface receptor proteins activates second messengers
  • signalling proteins and second messengers amplify, process and distribute incoming signals from both classes of signal receptor proteins
  • some signals sent to effector proteins in the cytosol (typically fast, short response to activation of pathway)
  • some pathways terminate at effectors in the nucleus, effectors are transcription factors that control gene expression, slower more prolonged response
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20
Q

signal transduction pathway types

A
  • linear
  • convergent
  • divergent
  • multi branched
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21
Q

linear signal transduction pathway

A

one receptor interacts with one signalling protein or secondary messenger

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22
Q

convergent signal transduction pathway

A

several receptors share common signalling proteins or second messengers

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23
Q

divergent signal transduction pathway

A

single receptor interact with multiple signalling proteins or second messengers

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24
Q

multi branched signal transduction pathway

A

combination of convergence and divergence may be happening all at the same time

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25
Q

what are signals + types

A

also called ligands (signal trigger molecule)

arise from extracellular space and must bind to receptor to be effective

membrane impermeable - cant penetrate membrane and bind to cell surface receptors

membrane permeable (mainly steroids) not limited to membrane receptors and can penetrate membrane and interact with cytosolic receptors

physical signals - pressure, temperature and light

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26
Q

receptors types

A
  • G protein coupled receptors (GPCR)
  • ion channels
  • guanylate cyclase
  • protein kinase receptors
  • transmembrane scaffolds
  • nuclear receptors
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27
Q

G protein coupled receptors (GPCR) function + structure

A

superfamily of receptors, involved in many reactions (smell, flight or fight response)

combination of seven transmembrane domains (H1 to H7) and a heterotrimeric G protein with alpha, beta, gamma subunits that interact with eachother

binding of ligands cause conformation shape change leading to activation of coupled G protein subunit

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28
Q

ion channel receptors function

A

transmit signal information allowing ions to flow from one side of the membrane to the other

undergo conformational shift that opens pores and allows ions to flow through

unlike other receptors proteins these are not enzymes

common for communication between nerve cells through the release of neurotransmitters

responsible for voluntary muscle contraction

29
Q

guanylate cyclase receptors structure + where its found

A

found both bound to membrane and soluble in cytosol

contain externalized ligand binding domain, transmembrane domain and internal catalytic domain

important for vision, convert light signal into electrical signal in eye

30
Q

guanylate cyclase function

A

soluble form serves as a target for some membrane soluble ligands and mediates some intracellular processes

when activated catalytic domain converts GTP into cyclic guanosine monophosphate (cGMP) which binds to other signalling proteins to initiate cellular processes

31
Q

protein kinase receptor function

A

note not all protein kinases are cell surface receptors

many are cytosolic proteins used in signal transduction, alter enzyme activity, etc

general action is to phosphorylate proteins with serine, threonine or tyrosine residues

32
Q

types of protein kinase receptor

A

receptor tyrosine kinases (RTK)

serine/threonine kinases receptors (S/TRK)

33
Q

process of protein tyrosine kinase receptor ligand binding

A

before ligand bind inactive receptors separate polypeptides with inactive tyrosine kinase domains

binding to signal cause two subunits of receptor to join (dimerize) forming a dimer (active now)

transautophosphorylation occurs when cytoplasmic tails of one subunit brought close to tyrosine kinase domain of other subunit and the opposite domain is phosphorylated on specific tyrosine amino acids

resulting phosphotyrsine amino acids are binding sites for more signalling proteins

ligand released, amino acids dephosphorylated by phosphoprotein phosphatase

kinase resets to inactive state

34
Q

transmembrane scaffold receptors

A

do not always have a distinct function

tends to form in large clusters of receptors and signalling proteins

scaffold proteins determine which signalling proteins can bind to a complex

35
Q

transmembrane scaffold receptors function

A
  • bring signalling proteins togetehr
  • regulate signal transduction
  • localize signalling proteins to specific cellular areas
  • isolate specific signalling pathways
36
Q

nuclear receptors

A

found inside cytosol

once ligand binds receptros move through nuclear pore complexes directly to the nucleus

class of receptor also called transcription factors

also play an important role in response to toxic substances

37
Q

nucelar receptor function

A

inside nucleus activated receptor binds to specific DNA sequence called steroid response elements (SREs) which controls expression of genes

38
Q

signalling proteins features

A

mobility
- highly mobile, can diffuse rapidly through cytosol/plasma membrane (membrane associated)

catalysis
- catalyze chemical reactions for signal amplification
- capable of binding to enzymes

39
Q

signalling proteins function

A

transmit and amplify signal information

also can mobilize second messengers (non protein) which link signalling proteins together, or have direct actions of their own

40
Q

G protein (signalling protein)

A

bind GTP and propagate signals

two different families monomeric G proteins and heterotrimeric G proteins, differ in number of polypeptides

41
Q

monomeric G proteins (signalling protein)

A

single polypeptides that contain two different binding sites (one for GTP/GDP and one for target protein) and a GTPase domain

not coupled to G protein coupled receptors

when GTP bound in activated state and can bind to target protein. GTPase then cleave GTP to form GDP which is eventually released so GTP can bind and reactivate

42
Q

heterotrimeric G protein

A

contain three different polypeptides

anchored to plasma membrane

activated by G protein coupled receptors

alpha subunit binds GTP/GDP and target protein

beta/gamma subunits attached together and stabilize inactive form of the alpha subunit (GDP bound)

43
Q

activity of G protein process

A

binding
- heterotrimer is bound to GDP (inactive)
- ligand binds the receptor changes conformation to interact with heterotrimeric G protein

seperation
- receptor causes exchange of GDP with GTP on alpha subunit
- heterotrimer separates into separate alpha and beta/gamma subunits (G protein active)

propagate
- while separated alpha and beta/gamma subunits bind downstream targets, propagating signal pathway
- subunits interact with different effectors

cleave and reform
- alpha subunits cleaves GTP to form GDP and subunits bind to reform heterotrimer
- returns to inactive form

44
Q

protein kinases (signalling protein)

A

enzymes that attach phosphate groups to tyrosine, serine and threonine amino acids

there are receptor and non receptor protein kinases (majority non, cytosolic signalling proteins)

cytosolic protein kinases act as intermediaries once active they active other protein kinases, other signalling proteins or directly phosphorylate effector proteins like enzymes

phosphorylation of target proteins can either active or inactive them

some can enter nucleus but do not interact with DNA directly, can phosphorylate proteins that do

45
Q

calcium binding proteins (signalling protein)

A

calcium kept at low intracellular concentration so when level increase due to signalling event, interact with certain proteins causing downstream effect

example
- CA2+ bind to calmodulin inducing conformational change that allows it to calmodulin to bind to target protein

46
Q

adenylyl cyclase (signalling protein)

A

converts ATP into cyclic AMP (cAMP)

not linked to membrane receptors

binds to alpha subunit of heterotrimeric G proteins so designated as signalling protein instead of receptor type

47
Q

subunits for adenylyl cyclase (signalling protein)

A

two types of heterotrimeric G protein alpha subunits
- as which stimulates adenylyl cyclase
- ai inhibits it

different forms of alpha subunit linked to different G protein coupled receptors

48
Q

lipid kinases (signalling protein)

A

phosphorylate phospholipids in the cytoplasmic leaflet of membrnae

add phosphate to polar head group, results in conformational change in phospholipid allowing it to bind to target protein in membrane to pass signal

some phospholipids can be phosphorylated more than once to become an active signalling molecule

49
Q

adaptor proteins (signalling proteins)

A

class of protein that is neither a receptor or enzyme

have different binding domains that recognize phosphorylated amino acids or other activated structures of signalling proteins

domains form the glue to hold elements of signalling networks together at right time and place in cell

important to allow cascade when and where needed

50
Q

what are second messengers

A

they are non protein ions or molecules formed/release during signal transduction

relay signalling information from signalling proteins to other cellular targets

51
Q

features of second messengers

A

small in size

rapidly diffuse in cytosol/membrane

amplify signals so the interaction of few ligands cause much larger response

do not live in the cytosol for long, degrade by specific enzymes (phosphodiesterase - cAMP/cGMP) or sequestered into cellular organelles (ionic messengers Ca2+)

52
Q

heterotrimeric G protein signalling cascade

A

GPCRs (receptor)
- pathway start by binding of ligad on GPCR
- binding of receptor allows receptor protein to interact with heterotrimeric G protein

cAMP
- receptor stimulates replacement of GDP for GTP in alpha subunit
- heterotrimeric G protein dissociates from receptor leaving beta/gammer subunit and an activated alpha subunit
- alpha subunit finds and activates signalling protein adenylyl cyclase to convert ATP into cAMP (second messenger)

PKA
- cAMP binds to another protein kinase A (PKA)
- binding to regulatory subunits cases protein to dissociate and release the active catalytic subunit
- catalytic subunit phosphorylate number of cellular proteins

CREB
- active PKA catalytic domains can enter nucleus
- targets cyclic AMPA response elemement binding protein (CREB)
- PKA phosphorylate so CREB binds CBP (CREB binding protein) which interact with DNA to initiate transcription

53
Q

phospholipid kinase signalling cascade

A

GPCR
- pathway start by binding of ligad on GPCR
- binding of receptor allows receptor protein to interact with heterotrimeric G protein
- receptor stimulates replacement of GDP for GTP in alpha subunit
- heterotrimeric G protein dissociates from receptor leaving beta/gammer subunit and an activated alpha subunit

PLC
- alpha subunits binds the phospholipid kinase signalling protein phospholipase C (PLC)

PIPI2/IP3
- activated PLC break down membrane phospholipid PIP2 to release two second messengers (disacyglycerol (DAG) and IP3)

Ca2+
- IP3 diffuses freely in cytosol to active ER receptors
- opens ligand gated calcium channel
- Ca2+ leaves ER acting as second messenger
- Ca2+ actives number of calcium binding proteins

PKC
- membrane bound DAG and Ca+ bind to protein kinase C (PKC)
- active PKC phosphorylate numerous cellular targets to modulate targets activity

54
Q

protein kinase signalling cascade

A

FGFs
- fibroblast growth factors (FGFs) bind to FGF receptors
- FGFR is a homodimeric (two identical protein subunits)
- binding of FGF to FGFR cause subunits to dimerize (come together)
- FGFG undergoes tyrosine transautophosphorylation to form phosphotyrosines on cytoplasmic side
- phosphotyrosines can be bound by a multitude of proteins

Grb2
- adaptor protein Grb2 bind to phosphotyrosine causeing confromational change of Grb2 to bind Sos
- Sos bind to monomeric G protein Ras, replaces GDP with GTP
- Ras bind to serine/threonine kinase called Raf
- Raf can phosphorylate the protein kinase MEK
- MEK phosphorylate another serine/threonine kinase (Erk)

Erk
- Erk forms dimer and can phosphorylate signalling proteins in cytosol or nucleus
- can enter nucleus to active transcription factors

55
Q

what are lysosomes

A

organelles that break down misfolded and damaged organelles, nucleic acids, lipids and more

56
Q

what are proteasomes

A

protein complexes that specifically break down damaged and misfolded proteins in the nucleus/cytosol

digest both soluble proteins and membrane proteins in the lysosome

57
Q

what are peroxisomes + function

A

small membrane enclosed organelle with enzymes

essential peroxisomes proteins called peroxins (synthesized in cytosol and targeted to peroxisomes by specific peroxisomal targeting signals (PTSs))

handle dangerous free radicals (reactive oxygen species) and important for decomposing some cargo (uric acid)

place to keep and use ROS safely

58
Q

vesicles role in cargo delivery to the lysosome

A

engulfed proteins delivered by vesicles that empty their content by fusing with the lysosome and are digested by the proteases

protease delivered to the lysosome via vesicle

59
Q

digestion in the lysosome

A

breakdown proteins not endogenous to the cell or from other cells

contain high concentration of proteases and enzymes that cleave and digest fats and sugars and can even engulf other organelles

one large molecules are broken down into basic parts, thy are transported to the cytosol for cell reuse

60
Q

proteasome protein degradation

A

proteasome required process of ubiquitination (transcriptional modification of proteins)

misfolded/damaged cytosolic proteins tagged with polyubiquitin chain (required for protein to be targeted and recognized)

in nucleus unwanted nuclear proteins are polyuiquinated then degraded by nuclear proteasome

61
Q

what is apoptosis

A

programmed cell death

energy consuming process that cleanly and carefully ends the life of a cell

protects the body from damaged cells

62
Q

mechanisms of apoptosis

A

initiation
- initiated by two pathways (intrinsic, extrinsic)

membrane blebbing and enzyme activation
- cell shrinks and forms blebs (small protrusions from plasma membrane), first visible signal
- caspases enzymes activate
- initiator caspases cleave and activate executioner caspases

cell structure change
- executioner caspases activation causes cell structure change
- DNA is fragmented (often between histones)
- DNA repair stops
- nuclear membrane breaks down and the nucleus disappears
- cytoskeleton disassembled
- plasma membrane phospholipid content changed with scramblases (PS exposed on exoplasmic leaflet)
- organelles persist and are encloses in apoptotic bodies

phagocytes
- phagocytes endocytose the apoptotic bodies to dispose of them (safely digested by the lysosomes)
- minimal disturbance to cells and surrounding tissue

63
Q

intrinsic pathway apoptosis

A

cell initiates it itself

pathway originates in outer membrane of mitochondria

intracellular signals (DNA damage, ROS toxins) turn on the pathway in the cell

64
Q

extrinsic pathway apoptosis

A

external signals initiate apoptosis

pathway uses a plasma membrane receptor called death receptor

neighbouring cells release death ligand which bind to death receptor activating signals

65
Q

what is necrosis

A

accidental cell death

result of severe cellular injury unable to be repaired

organelles cant function so it dies

66
Q

injured cell response

A

attempt to repair

stressed cell show swelling in mitochondria and ER or some blebbing

if able to recover return to normal

67
Q

causes on necrosis

A
  • toxins
  • extreme heat or radiation
  • freezing
  • ischemia
  • pathogens
  • mechanical trauma
68
Q

mechanisms of necrosis

A

damage
- cell damaged beyond repair

swelling
- organelles lose structure and swell
- vacuoles or undefined bodies form in cell
- depending on damage DNA may degrade

destruction
- cell membrane and remaining organelles lose structural integrity
- cellular content spill, cause inflammatory signals
- mitochondria proteins released and lysosomal contents exposed
- cells nearby exposes and are damaged or apoptosis signalling is triggered

PHGY 170 (8 decks)

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