Functional Polarity

Question 1

what does a simple polarised cell look like?

Answer 1

a standard cell with differing apical and basolateral surfaces?

Question 2

what’s a highly polarized cell?

Answer 2

neuron

Question 3

what 3 components make up cell cytoskeleton?

Answer 3

microtubules
microfilaments
intermediate fibres

Question 4

what are microtubules made of?

Answer 4

tubulin

Question 5

in which direction do microtubules grow?

Answer 5

radially- from nucleus outwards

Question 6

what are microfilaments made of?

Answer 6

actin

Question 7

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

Answer 7

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

Question 8

what does a developing neuron look like?

Answer 8

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

Question 9

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

Answer 9

plated neurons make lamellopedia

Question 10

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

Answer 10

neurons extend in several places- short processes of equal length

Question 11

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

Answer 11

one process begins growing rapidly and acquires axonal features

Question 12

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

Answer 12

remaining processes grow slowly and acquire dendrite characteristics

Question 13

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

Answer 13

neurons are fully polarized and synapses begin to form

Question 14

what drives neuronal polarity?

Answer 14

cytoskeleton

Question 15

which of the 3 cytoskeleton components have polarity?

Answer 15

microtubules

microfilaments

Question 16

describe the axon in terms of cytoskeleton

Answer 16

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

Question 17

describe the dendrites in terms of cytoskeleton

Answer 17

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

Question 18

how long are microtubules?

Answer 18

25nm

Question 19

what, structurally are microtubules?

Answer 19

hollow tubes

Question 20

what binds microtubules?

Answer 20

GTP

Question 21

how long are intermediate filaments?

Answer 21

10 nm

Question 22

what, structurally are intermediate filaments like?

Answer 22

rope- like

Question 23

how long are microfilaments?

Answer 23

7nm

Question 24

what, structure do microfilaments have?

Answer 24

helical

Question 25

what binds microfilaments?

Answer 25

actin

Question 26

how do microtubules form?

Answer 26

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

Question 27

what end is exposed in a-tubulin?

Answer 27

-

Question 28

what end is exposed in B-tubulin?

Answer 28

+ (fast growing)

Question 29

what are the subunits of tubulin?

Answer 29

enzymes that catalyyze GTP to GDP

Question 30

how do subunits add and leave tubulin?

Answer 30

T-form recruited at +end | D-form shed from minus end (as - end is less stable)

Question 31

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

Answer 31

treadmilling

Question 32

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

Answer 32

dynamic instability (shrink)

Question 33

what influence the rate at which microtubules grow?

Answer 33

MAPs - bind +end

Question 34

what are the subunits in neuronal intermediate fibres?

Answer 34

neurofilaments

Question 35

what are neurofilaments abundant in?

Answer 35

myelinated axon

Question 36

what are the 3 types of NF filament?

Answer 36

light medium heavy

Question 37

how do intermediate fibres form?

Answer 37

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

Question 38

do neurofilaments have polarity?

Answer 38

no

Question 39

what do tail domains of H and M neurofilaments do?

Answer 39

radiate outwards due to extensive -ve charges

Question 40

what forms the bulk of the axon?

Answer 40

neurofilaments

Question 41

what in the axon do neurofilaments dictate?

Answer 41

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

Question 42

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

Answer 42

dictate the speed of nerve conduction

Question 43

structurally, what do intermediate filaments provide the neuron with?

Answer 43

tensile strength

Question 44

why are neurofilaments spaced out evenly through the axon?

Answer 44

mutual -ve charge repulsion

Question 45

what's similar between actin and tubulin?

Answer 45

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

Question 46

what's different between actin and tubulin?

Answer 46

actin uses ATP, tubulin GTP | actin in a right- handed helix

Question 47

where is actin particularly dense?

Answer 47

below the cell membrane

Question 48

what do integrins do?

Answer 48

link actin in cytoskeleton with extracelluar matrix

Question 49

How do scientists study axonal protein transport?

Answer 49

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

Question 50

is axonal transport passive or active?

Answer 50

active

Question 51

is there one or many shapes of dendrite?

Answer 51

many

Question 52

what are the structural characteristics of dendrites? (5)

Answer 52

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

Question 53

zooming on dendritic region what are the strcutures?

Answer 53

dendritic region > branchlet > spine cluster > spine

Question 54

how are dendrite spines imaged in vitro?

Answer 54

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

Question 55

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

Answer 55

``` filopodium thin stubby mushroom cup ```

Question 56

what changes spines?

Answer 56

age and experience

Question 57

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

Answer 57

spinogenesis- new spines forming

Question 58

what's happening to spines during adolescence?

Answer 58

lots of new spines forming

Question 59

what's happening to spines during early adulthood?

Answer 59

mass spine pruning of unused spines

Question 60

what's happening to spines during adulthood?

Answer 60

maintenance, some pruned some new

Question 61

give examples of 2 disorders with decreased spines

Answer 61

down syndrome | epilepsy

Question 62

what's been found about spines from honey bees?

Answer 62

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

Question 63

what do dendritic spines serve at?

Answer 63

calcium concentrating comapartments- for signals

Question 64

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

Answer 64

Axon Initial Segment (AIS)

Question 65

what does the AIS act as?

Answer 65

a physical diffusion barrier between somatodendritic and axonal compartment

Question 66

is the AIS often or rarely innervated?

Answer 66

rarely

Question 67

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

Answer 67

GABA- inhibitory- shuts down inputs

Question 68

what's the axon rich in?

Answer 68

actin and ankynin G

Question 69

what is ankynin G used for?

Answer 69

localising and immobilising sodium channels

Question 70

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

Answer 70

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

Question 71

describe axon structure?

Answer 71

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

Question 72

are axons often or rarely innervated?

Answer 72

rarely

Question 73

what myelinates axons in PNS?

Answer 73

schwann cells

Question 74

what myelinates axons in CNS?

Answer 74

oligodendrocytes

Question 75

what's non decremental energy?

Answer 75

no energy lost

Question 76

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

Answer 76

many little ones overlapping in parallel

Question 77

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

Answer 77

+ ends

Question 78

what's fast axonal transport?

Answer 78

membrane bound protein movement at 200-400 mm a day

Question 79

what's slow axonal transport?

Answer 79

membrane bound protein movement at 0.1-200mm a day

Question 80

what's anterograde transport?

Answer 80

from soma to axon end/ synapse

Question 81

what's reterograde transport?

Answer 81

from axon end to soma

Question 82

what does fast anterograde transport carry (2)

Answer 82

- membranous organelles e.g. mitochondria | - vesicles carrying neurotransmitters and enzymes for activation

Question 83

what is fast anterograde transport mediated by?

Answer 83

kinesins

Question 84

what are kinesins?

Answer 84

specialised microtubule binding proteins

Question 85

how many members of the kinesin family?

Answer 85

14

Question 86

what's the structure of kinesin?

Answer 86

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

Question 87

how do kinesins move?

Answer 87

``` 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 ```

Question 88

how are kinesin families catergorized?

Answer 88

by the position of their motor domain on the microtubule

Question 89

what are the 3 families of kinesin?

Answer 89

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

Question 90

what drives microfilament movement?

Answer 90

myosin

Question 91

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

Answer 91

kinesin on microtubule

Question 92

what is carried by fast retrograde axonal transport?

Answer 92

- endosomes - mitochondria etc. to soma for degradation by lysosomes and recycling

Question 93

what takes advantage of fast anterograde axonal transport?

Answer 93

toxins | viruses e.g. HIV and tetanus

Question 94

which protein performs fast retrograde axonal transport?

Answer 94

dynein - along microtubule tracks

Question 95

is dynein large or small?

Answer 95

large

Question 96

what end of microtubule does dynein bind?

Answer 96

- end

Question 97

what's required for dynein binding to microtubule?

Answer 97

dynactin association binding to MT

Question 98

what allowd dynein movement?

Answer 98

ATPase activity

Question 99

what does slow axonal transport carry?

Answer 99

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

Question 100

what's the mechanism of slow axonal transport?

Answer 100

- v.slow - uses diffusion - stop and go-- fast movement but prolonged pauses

Question 101

what 4 factors govern the rate of axonal transport?

Answer 101

- cargo - type of motor - number of stops - changing of motor/tracks