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HELENP CBG: Cell Architecture, Communication and Regulation > CBG Lecture 37:Cytoskeleton > Flashcards

CBG Lecture 37:Cytoskeleton Flashcards

1
Q

what are the main roles of the CSK in eukaryotes

A

support of cell shape: microvilli, cell cortex
intracellular traffic - guides moving vesicles
cell division - mitotic spindle
motion - cell migratoin, muscle contraction

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2
Q

within a cell, where is microtubules/actin

A

microtubles arranged from centre outwords

actin generally on periphary/circumference

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3
Q

how does CSK help in support

A

microvilli

cell cortex

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4
Q

how does CSK help in intracellular traffic

A

guides moving vesicles

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5
Q

how does CSK help in cell division

A

separation of spindle poles

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6
Q

how does CSK help in motion

A

filapodia

flagella

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7
Q

what is CSK essential for

A

wound healing
sperm-egg fusion
muscle function

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8
Q

what are the 3 distinct subregions of CSK

A
  1. microtubules:detemine organell position
  2. intermediate filaments:give mechanical strength
  3. microfilaments - actin filaments: give cell surface shape
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9
Q

what is a microfilament, and its role

A

actin

gives cell surface shape

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10
Q

what do intermediate filaments do

A

give mechanical strength

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11
Q

what do microtubules do

A

determine organelle position

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12
Q

what do motor proteins do

A

move organelles along the filaments of move the filaments themselves

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13
Q

what do all 3 filaments (microfilaments,intermediate filaments, microtubules) have in common

A

all form as helical assemblies of subunits that self-associate using a ocmbo of end to end and side to side protein contacts

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14
Q

discuss structure of intermediate filaments

A

rope like and hard to break but easy to bend

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15
Q

give structure of microtubules

A

strong rigid hollow tubes

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16
Q

give structure of microfilaments (actin filaments)

A

thinnest of the 3, hard to stretch but easy to break

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17
Q

whatis base unit of mictrotubules

A 
alpha/beta tubulin heterodimer
hollow cylindrical polymer
polar filament
stiff/rigfid
GTP hydrolysis has major effect on microtubule dynamics
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18
Q

what is outer diameter of microtubules

A

25nm

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19
Q

what do microtubules typically have one end attacxhed to

A

a single MTOC (micrtubule organising centre) called a centrosome

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20
Q

talk about microtubule dynamics

A

beta tubulin binds GTP during polymerization, this molecule hydrolysed to GDP
GDPbound form of tubulin is unstable in the microtubule and causes microtubules to shrink between shrinking (catastrophe) and growing (rescue) phases
alpha tubulin is ALWAYS in its GTP-bound state and has a structural role
GTP hydrolysis puts the lattice under stress
when cap is lost microtubule depolmerises and peels apart

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21
Q

discuss microtubule organisation

A

centrosomes are MTOCs - microtubule organisation centres
gamma tubulin ring complex (gamma-TURC) within MTOC nucleates microtubule assembly
grow from + end
centrosome (interphase) spindle poles (mitosis) are MTOCs

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22
Q

what does gamma TURC do

A

within MTOC and nucleates microtubule assembly

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23
Q

name an MTOC in mitosis

A

spindle poles

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24
Q

name an MTOC in interphase

A

centrosome

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25
Q

how can microtubules be used to treat disease

A

controlling microtubule dynamics can treat gout

colchicine - affects tubulin dynamics by inhibiting polymerization and therefore relieves gout joint pain

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26
Q

name drugs that prevent polymerization of tubulin

A

Colchicine was first known drug

Taxol is moder drug that inhibits mitosis and used to treat some breast/ovarian cancers

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27
Q

what is movement along mictubules (MT) based on

A

the action of motor proteins that utilize energy derived from ATP hydrolysis to produce force and movement
such proteins: kinesin, dynein

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28
Q

what do kinesin and dynein do

A

move cargo along microtubule tracks

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29
Q

what are kinesins

A

transport cargo towards + end MT via a processive movement - lots of contact, never dissociates from MT
eg. carries NTs from Golgi to terminal branches of aoxn, generally carries AWAY from centre

30
Q

discuss structure of kinesins

A

2 heavy chains wound round eachother in coiled coil and two light chains
the globular head domains of the heavy chains bind MTs and are the motor domains of the molecule

31
Q

what end does kinesin transport cargo to

A

kinesin transports cargo to the + end of the MT

32
Q

what are dynein proteins

A

motorprotien which requires qaccessory proteins to make a dynactin complex

33
Q

in what direction does dynein transport cargo

A

form axon BACK to cell body - eg when no NT left

generally TOWARD centre

34
Q

outline structure of dynein

A

2/3 heavy chain in association with multiple light and intermediate chains
the globular head domains of the heavy chains are the motor domains

35
Q

outline “kinesin walking”

A

when one of the two kinesin heads encounters a MT it bind tightly
MT binding causes ADP release from attached heads
ATP then rapidly enters the empty nucleotide binding site - nucleotide exchange triggers the neck linker to zipper onto catalytic core
this action throws the second head forward and brings it near next binding site on MT
the attached trailing head hydrolyses ATP and releases Phosphate
as the neck linker unzippers from the trailing head, the leading head exchanges its nucleotide (ADP for ATP) and zippers its neck linker onto catalytic core

36
Q

what does processive movelment along MT mean? what does this

A

kinesin does this

it means step by step

37
Q

describe intermediate filaments

A

provide mechanical strength - dont serve as tracks for motor proteins, less dynamic
various subunits
no polarity

38
Q

do intermediate filaments have polarity

A

no

39
Q

give some examples of intermediate filaments

A

keratins

lamins (nucleus)

40
Q

what filaments are lamins an example of

A

intermediate filaments

41
Q

what residues are keratins rich in

A

cysteine- form disulfide bonds

42
Q

which filaments hve subunits that DONT bind nucleotides

A

intermediate filaments

43
Q

what are actin filaments

A

microfilaments

44
Q

what do microfilaments do

A

determine the shape of the cells surface and necessary for whole cell locomotion
serve as tracks for motor protein myosin
line the perimeter of cell and give shape to microvilli

45
Q

what is the base unit of microfilaments

A

an actin monomer G actin
G actin assembles into a linear filament of F actin - 2 helices
F actin ha spolarity

46
Q

in microfilaments, where is the nucleotide binding site

A

on - end as it is polar

47
Q

at what end to microfilaments grow faster

A

positive ends

48
Q

name some cellular structures uysed by cells to explore territory and pull themselves around

A

lemellipodia

filopodia

49
Q

what is actin filament made of

A

2 parallel protofilaments that twist round eachother in a right handed helix

50
Q

what is profilin

A

recharges ADP-actin

51
Q

what is cofilin

A

binds ADP-F-actin and destabilizes the filament, untwist

52
Q

how are actins organised

A

by crosslinking proteins

filaments attach laterally at the (+) end to the PM

53
Q

what is the term given to actin for how it grows

A

treadmilling

54
Q

what is treadmilling

A

actin dynamics - made possible by the nucleoside triphosphate hydrolysis that follows subunit addition

55
Q

what gives directionality to actin dynamics

A

filament growth from + end, ADP actin disassembles from - end
profilin recharges and allows regrowth
cofilin binds ADP-F-actin and destabilises the filament causing untwisting

56
Q

discuss movement along actin filaments

A

myosin motor proteins move along actin tracks
myosin structure: head domain - motor
neck domain -lever arm
tail domain -cargo binding

57
Q

which part of myosin is the cargo binding, and lever arm

A

`cargo binding - tail domain

neck domain -lever arm

58
Q

how is myosin movement powered

A

ATP hydrolysis

59
Q

what is function of myosin 2

A

muscle contraction

move towards + end

60
Q

what is function of myosin 4

A

`transport vesicular cargo
move towards - end
endocytosis

61
Q

which myosin involved in muscle contraction

A

myosin 2

62
Q

which myosin involved in vesicular cargp transport

A

myosin 4

63
Q

outline myosin movement

A

1`.prestroke ADP-Pi form

  1. actin binding triggers release Pi, converts to post stroke ADP form
  2. ADP dissociates, ATP binds triggers detachment
64
Q

what is power stroke

A

generation of tensile force

65
Q

what od myosin motor proteins do

A

control actin dynamics during muscle contraction

66
Q

what makes up individual muscle fibres

A

laterally aligned muscle fibres

67
Q

what are myofibrils made up of

A

sarcomeres which are assemblies of actin and myosin microfibrils

68
Q

what does myosin do

A

binds and hydrolyses ATP which drives its movement along actin filament

69
Q

what are actin filaments anchored by in the sarcomere

A

anchored by plus end to Z disc

70
Q

what happens in the sliding filament mechanism

A
  • contraction begins with the head of myosin molecules bound to actin on actin filament
    while still bound to actin, the myosin head fibres, pulling the actin filament along with it - this causes actin filament to slide by myosin filament
    myosin head then releases from the actin and unflexes - change powered by ATP hydrolysis
    this frees the myosin head to bind with a different actin molecule

HELENP CBG: Cell Architecture, Communication and Regulation (5 decks)

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