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Membrane Excitability > Functional Polarity > Flashcards

Functional Polarity Flashcards

1
Q

what does a simple polarised cell look like?

A

a standard cell with differing apical and basolateral surfaces?

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2
Q

what’s a highly polarized cell?

A

neuron

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3
Q

what 3 components make up cell cytoskeleton?

A

microtubules
microfilaments
intermediate fibres

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4
Q

what are microtubules made of?

A

tubulin

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5
Q

in which direction do microtubules grow?

A

radially- from nucleus outwards

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6
Q

what are microfilaments made of?

A

actin

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7
Q

what’s the order of transmission of a neuron- starting from synapse?

A

synapse –> dendrite –> cell body–> axon–> synapse

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8
Q

what does a developing neuron look like?

A

cell body with branching neurites and a growth cone and end with filopedia coming out

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9
Q

what happens during stage 1 (day 0) of neuron development?

A

plated neurons make lamellopedia

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10
Q

what happens during stage 2 (day 0.5) of neuron development?

A

neurons extend in several places- short processes of equal length

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11
Q

what happens during stage 3 (day 1) of neuron development?

A

one process begins growing rapidly and acquires axonal features

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12
Q

what happens during stage 4 (day 4) of neuron development?

A

remaining processes grow slowly and acquire dendrite characteristics

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13
Q

what happens during stage 5 (days 7-10) of neuron development?

A

neurons are fully polarized and synapses begin to form

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14
Q

what drives neuronal polarity?

A

cytoskeleton

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15
Q

which of the 3 cytoskeleton components have polarity?

A

microtubules

microfilaments

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16
Q

describe the axon in terms of cytoskeleton

A

all microtubules orientated with + ends outwards and associate with specific binding proteins to become stabilized polymers

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17
Q

describe the dendrites in terms of cytoskeleton

A

start with being all +end microtubules, but later become mixed with + and - ends facing both directions

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18
Q

how long are microtubules?

A

25nm

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19
Q

what, structurally are microtubules?

A

hollow tubes

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20
Q

what binds microtubules?

A

GTP

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21
Q

how long are intermediate filaments?

A

10 nm

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22
Q

what, structurally are intermediate filaments like?

A

rope- like

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23
Q

how long are microfilaments?

A

7nm

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24
Q

what, structure do microfilaments have?

A

helical

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25
Q

what binds microfilaments?

A

actin

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26
Q

how do microtubules form?

A

a and B tubulin are globular proteins
dimerise to form a aB heterodimer
polymerise to form protofilament chain
lateral interactions between a to a and B to B chains form a cylindrical microtubule structure- mature

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27
Q

what end is exposed in a-tubulin?

A

-

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28
Q

what end is exposed in B-tubulin?

A

+ (fast growing)

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29
Q

what are the subunits of tubulin?

A

enzymes that catalyyze GTP to GDP

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30
Q

how do subunits add and leave tubulin?

A

T-form recruited at +end

D-form shed from minus end (as - end is less stable)

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31
Q

what’s it called when a tubulin polymer is at constant length?

A

treadmilling

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32
Q

what’s it called when tubulin GTP hydrolysis is faster that subunit addition?

A

dynamic instability (shrink)

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33
Q

what influence the rate at which microtubules grow?

A

MAPs - bind +end

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34
Q

what are the subunits in neuronal intermediate fibres?

A

neurofilaments

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35
Q

what are neurofilaments abundant in?

A

myelinated axon

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36
Q

what are the 3 types of NF filament?

A

light
medium
heavy

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37
Q

how do intermediate fibres form?

A

the neurofilaments form dimers, then tetramers then 8 tetramers associate to form rope-like filaments

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38
Q

do neurofilaments have polarity?

A

no

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39
Q

what do tail domains of H and M neurofilaments do?

A

radiate outwards due to extensive -ve charges

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40
Q

what forms the bulk of the axon?

A

neurofilaments

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41
Q

what in the axon do neurofilaments dictate?

A

the width - as they are added along the width as well as the ends

42
Q

by dictating the width of the axons, what do neurofilaments therefore do?

A

dictate the speed of nerve conduction

43
Q

structurally, what do intermediate filaments provide the neuron with?

A

tensile strength

44
Q

why are neurofilaments spaced out evenly through the axon?

A

mutual -ve charge repulsion

45
Q

what’s similar between actin and tubulin?

A

made up of a globular peptide
binding site for substrate
polarity - undergo treadmilling

46
Q

what’s different between actin and tubulin?

A

actin uses ATP, tubulin GTP

actin in a right- handed helix

47
Q

where is actin particularly dense?

A

below the cell membrane

48
Q

what do integrins do?

A

link actin in cytoskeleton with extracelluar matrix

49
Q

How do scientists study axonal protein transport?

A

cutting/tying an axon at a certain point. take different segments and see where protein accumulates - find direction of travel

50
Q

is axonal transport passive or active?

51
Q

is there one or many shapes of dendrite?

52
Q

what are the structural characteristics of dendrites? (5)

A

tapered, branched, emerge from soma, continuous cytoplasm with soma

53
Q

zooming on dendritic region what are the strcutures?

A

dendritic region > branchlet > spine cluster > spine

54
Q

how are dendrite spines imaged in vitro?

A 
mouse
kill mouse
remove brain
microdissect desired brain region
cut 200 micrometre sections
transfect/ GFP tags
image
55
Q

what are the different morphologies of dendritic spines going from immature to mature?

A 
filopodium
thin
stubby
mushroom
cup
56
Q

what changes spines?

A

age and experience

57
Q

what’s happening to spines during early post-natal life?

A

spinogenesis- new spines forming

58
Q

what’s happening to spines during adolescence?

A

lots of new spines forming

59
Q

what’s happening to spines during early adulthood?

A

mass spine pruning of unused spines

60
Q

what’s happening to spines during adulthood?

A

maintenance, some pruned some new

61
Q

give examples of 2 disorders with decreased spines

A

down syndrome

epilepsy

62
Q

what’s been found about spines from honey bees?

A

older, more experienced foraging bees have more spines about younger/less experienced ones and loads more than nurses (who stay in the hive)

63
Q

what do dendritic spines serve at?

A

calcium concentrating comapartments- for signals

64
Q

what’s the name of the firs segment of axon coming out of soma?

A

Axon Initial Segment (AIS)

65
Q

what does the AIS act as?

A

a physical diffusion barrier between somatodendritic and axonal compartment

66
Q

is the AIS often or rarely innervated?

67
Q

what neurotransmitters do the few axons that synapse onto the AIS use?

A

GABA- inhibitory- shuts down inputs

68
Q

what’s the axon rich in?

A

actin and ankynin G

69
Q

what is ankynin G used for?

A

localising and immobilising sodium channels

70
Q

in what 2 ways are Na+ channels compartmentalised at AIS?

A

Direct transport- when they are inserted into the AIS membrane
or
Elimination/ retention- they are produced evenly spread throughout neuron and removed everywhere other than AIS by endocytosis

71
Q

describe axon structure?

A

long, untapered, cylindrical, 1 micrometre thick, can have collateral branches at 90 degrees, can be myelinated

72
Q

are axons often or rarely innervated?

73
Q

what myelinates axons in PNS?

A

schwann cells

74
Q

what myelinates axons in CNS?

A

oligodendrocytes

75
Q

what’s non decremental energy?

A

no energy lost

76
Q

are axons made up of one long tubule or many little ones?

A

many little ones overlapping in parallel

77
Q

in a axon, which end of microtubules are pointing outwards?

78
Q

what’s fast axonal transport?

A

membrane bound protein movement at 200-400 mm a day

79
Q

what’s slow axonal transport?

A

membrane bound protein movement at 0.1-200mm a day

80
Q

what’s anterograde transport?

A

from soma to axon end/ synapse

81
Q

what’s reterograde transport?

A

from axon end to soma

82
Q

what does fast anterograde transport carry (2)

A
  • membranous organelles e.g. mitochondria

- vesicles carrying neurotransmitters and enzymes for activation

83
Q

what is fast anterograde transport mediated by?

84
Q

what are kinesins?

A

specialised microtubule binding proteins

85
Q

how many members of the kinesin family?

86
Q

what’s the structure of kinesin?

A

2 globular motor domains (ATP binding sequence and microtubule binding sequence)
filamentous stalk
cargo-binding site in tail region - for vessicles/ membranous organelles

87
Q

how do kinesins move?

A 
2 globular heads
motor head binds microtubule
ATP associates with molecule 
ATP hydrolysis causes a conformational change in kinesin , new association with molecule is formed
-1 step
88
Q

how are kinesin families catergorized?

A

by the position of their motor domain on the microtubule

89
Q

what are the 3 families of kinesin?

A

N- kinesin- bind NH- terminal
M-kinesin- bind middle of microtubule
C- kinesin- bind -COOH end (- end)

90
Q

what drives microfilament movement?

91
Q

what’s faster myosin on microfilament or kinesin on microtubule?

A

kinesin on microtubule

92
Q

what is carried by fast retrograde axonal transport?

A
  • endosomes
  • mitochondria
    etc. to soma for degradation by lysosomes and recycling
93
Q

what takes advantage of fast anterograde axonal transport?

A

toxins

viruses e.g. HIV and tetanus

94
Q

which protein performs fast retrograde axonal transport?

A

dynein - along microtubule tracks

95
Q

is dynein large or small?

96
Q

what end of microtubule does dynein bind?

97
Q

what’s required for dynein binding to microtubule?

A

dynactin association binding to MT

98
Q

what allowd dynein movement?

A

ATPase activity

99
Q

what does slow axonal transport carry?

A

cytosolic and cytoskeletal proteins and enzymes for small neurotransmitter synthesis from soma to axon terminal

100
Q

what’s the mechanism of slow axonal transport?

A
  • v.slow
  • uses diffusion
  • stop and go– fast movement but prolonged pauses
101
Q

what 4 factors govern the rate of axonal transport?

A
  • cargo
  • type of motor
  • number of stops
  • changing of motor/tracks

Membrane Excitability (9 decks)

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