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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
how can microtubules be used to treat disease
controlling microtubule dynamics can treat gout | colchicine - affects tubulin dynamics by inhibiting polymerization and therefore relieves gout joint pain
26
name drugs that prevent polymerization of tubulin
Colchicine was first known drug | Taxol is moder drug that inhibits mitosis and used to treat some breast/ovarian cancers
27
what is movement along mictubules (MT) based on
the action of motor proteins that utilize energy derived from ATP hydrolysis to produce force and movement such proteins: kinesin, dynein
28
what do kinesin and dynein do
move cargo along microtubule tracks
29
what are kinesins
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
discuss structure of kinesins
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
what end does kinesin transport cargo to
kinesin transports cargo to the + end of the MT
32
what are dynein proteins
motorprotien which requires qaccessory proteins to make a dynactin complex
33
in what direction does dynein transport cargo
form axon BACK to cell body - eg when no NT left | generally TOWARD centre
34
outline structure of dynein
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
outline "kinesin walking"
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
what does processive movelment along MT mean? what does this
kinesin does this | it means step by step
37
describe intermediate filaments
provide mechanical strength - dont serve as tracks for motor proteins, less dynamic various subunits no polarity
38
do intermediate filaments have polarity
no
39
give some examples of intermediate filaments
keratins | lamins (nucleus)
40
what filaments are lamins an example of
intermediate filaments
41
what residues are keratins rich in
cysteine- form disulfide bonds
42
which filaments hve subunits that DONT bind nucleotides
intermediate filaments
43
what are actin filaments
microfilaments
44
what do microfilaments do
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
what is the base unit of microfilaments
an actin monomer G actin G actin assembles into a linear filament of F actin - 2 helices F actin ha spolarity
46
in microfilaments, where is the nucleotide binding site
on - end as it is polar
47
at what end to microfilaments grow faster
positive ends
48
name some cellular structures uysed by cells to explore territory and pull themselves around
lemellipodia | filopodia
49
what is actin filament made of
2 parallel protofilaments that twist round eachother in a right handed helix
50
what is profilin
recharges ADP-actin
51
what is cofilin
binds ADP-F-actin and destabilizes the filament, untwist
52
how are actins organised
by crosslinking proteins | filaments attach laterally at the (+) end to the PM
53
what is the term given to actin for how it grows
treadmilling
54
what is treadmilling
actin dynamics - made possible by the nucleoside triphosphate hydrolysis that follows subunit addition
55
what gives directionality to actin dynamics
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
discuss movement along actin filaments
myosin motor proteins move along actin tracks myosin structure: head domain - motor neck domain -lever arm tail domain -cargo binding
57
which part of myosin is the cargo binding, and lever arm
`cargo binding - tail domain | neck domain -lever arm
58
how is myosin movement powered
ATP hydrolysis
59
what is function of myosin 2
muscle contraction | move towards + end
60
what is function of myosin 4
`transport vesicular cargo move towards - end endocytosis
61
which myosin involved in muscle contraction
myosin 2
62
which myosin involved in vesicular cargp transport
myosin 4
63
outline myosin movement
1`.prestroke ADP-Pi form 2. actin binding triggers release Pi, converts to post stroke ADP form 3. ADP dissociates, ATP binds triggers detachment
64
what is power stroke
generation of tensile force
65
what od myosin motor proteins do
control actin dynamics during muscle contraction
66
what makes up individual muscle fibres
laterally aligned muscle fibres
67
what are myofibrils made up of
sarcomeres which are assemblies of actin and myosin microfibrils
68
what does myosin do
binds and hydrolyses ATP which drives its movement along actin filament
69
what are actin filaments anchored by in the sarcomere
anchored by plus end to Z disc
70
what happens in the sliding filament mechanism
- 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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