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Cell Organisation And Movement Flashcards

(36 cards)

1
Q

Micro filament definition
Sickle cell
Metastasis

A

Actin polymers organised by actin binding proteins
Plasma membrane integrity and micro villi
Tracks for ATP myosin motor proteins -> muscle contraction
Facilitates endocytosis

Sickle cell- b-globulin haemoglobin chain, aggregation under low O2. Cytoskeleton more rigid

Metastasis- changes in actin regulation allows non motile cells to move.

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2
Q

Micro tubules definition
Colchicine
Taxol

A

Formed by Tubulin, organised by micro tubule associated protein
Framework for organelles and support cilia and flagella
Structure of the mitotic spindle
Kinesins and dyneins transport

Colchicine- meadow saffron. Inhibits polymerisation of Tubulin. Relieve gout joint pain. Reduces micro tubule dynamics in WBCs so cannot migrate.

Taxol- plant alkaloid. Binds and stabilises micro tubules. Prevents cells from mitosis. Cancer treatment.

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3
Q

Intermediate filaments definition

A

Support, integrity, barrier. Not transport. A tetra ear is formed by side to side aggregation to form protofibril.
Neurofilaments- axon organisation
Lamins- inner surface nuclear membrane. Mutations cause emery-dreifus muscular dystrophy. Hutchinson-Guildford progeria (accelerated ageing)

Keratin- strength to epithelial cells. Epidermolysis bullosa- skins blisters.

Desmin, GFAP, vimentin

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4
Q

Coordinating the migrating cell cytoskeleton

A

Motility stimulus
Activation of signal cascade
cdc42 -> polymerisation of actin -> crawling
Also promotes micro tubules to direct secretory vesicles and adhesion molecules and nucleus movement

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5
Q

Structure of actin

A

F-actin - constructed of G actin monomers. Each actin molecule contains an Mg2+ complexed to ADP or ATP. G actin is divided into 2 lobes and ATP binds to bottom of the central cleft.
Addition of cations promotes formation of filaments
+ end is the joining end
One unit is 28 G actins

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6
Q

Actin polymerisation

A

Nucleation- ATP-G actin monomers form complexes. Rate limiting step. 3 monomers needed. Critical concentration required.
Elongation- stable nuclei elongate, addition to both ends
Steady state- equilibrium of addition/subtraction

Faster addition to + end as lower critical concentration.
When Pi is released, ATP at + and ADP at -
This then promotes dissociation from the - end

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7
Q

The cofilin cycle (actin polymerisation)

A

Cofilin binds to f and g actin. Specifically binds to ADP actin at the - end.
Bridges 2 adjacent actin monomers and changes twist -> destabilises
Increases the ADP actin that can be used by Profilin

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8
Q

The profilin cycle (actin polymerisation)

A

Profilin binds G actin on the opposite side to the ATP binding site
Binds and removes the ADP, monomer free to bind ATP
Profilin-ATP-G actin binds to + end and profilin dissociates

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9
Q

The Thymosin-β4 cycle (actin polymerisation)

A

Binds to G-ATP actin and inhibits addition. Creates G-actin reserve that can be used in blood clotting
CapZ caps the + end and stabilises, regulated by lipid.
Tropomodulin caps -end, abundant in cells that are stable e.g. RBCs and muscle
Gelsolin- binds to + end, regulated by Ca. Allows binding to side of an actin filament, creating new - end.

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10
Q

Mechanism of actin filament branching

A

Arp2/3 binds to side of filament (7 subunits)
WASp binds (NPF)-> conformational change allowing complex to bind actin
Filament formation
WASp has an RBD element that binds to Cdc42. Releases the ve terminal domain and activates.

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11
Q

Wiskott Aldrich syndrome

A

WASp defect. Not enough IgM produced, lack of platelets. X linked.

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12
Q

Listeria motility

A

Polymerises actin into a comet like tail. ActA is a Arp2/3 activating protein. Leads to actin nucleation of branched filaments -> force

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13
Q

Formins

A

Assemble unbranched filaments, FH1 FH2 adjacent domains with RBD. The FH1 contains Pro -> profilin binding. Increases concentration of ATP-G actin bound to profilin. Protects + from capping
FH2 inactive when associated to RBD. When bound to GTPase Rho, both domains exposed -> actin nucleation

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14
Q

Actin based cellular structures
Cross linkers
Spectrin

A

Cross linkers- 2 actin binding sites within polypeptide. Fimbrin is an example, arranges filament with polarity in bundles.
Also formed when 1 actin site dimerises. These are more spaced out, a-actinin is example.

Spectrin- tetramer with 2 sites, forms networks under the plasma membrane. Cross linkers such as filamin serve as springs at leading edges.

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15
Q

Diseases of the cytoskeleton

A

Arthritis
Osteoporosis- bone loses calcium and becomes thinner
Fibrodysplasia ossificans progressive- fibrous tissue ossified when damaged. Joints become frozen.

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16
Q

How are actin filaments linked to membranes in RBCs

A

2x14 subunit filaments. Stabilised by tropomyosin and tropomodulin
Linked together by Spectrin
Spectrin links to Ankyrin -> transmembrane protein band 3
Spectrin links to band 4.1 to transmembrane protein glycophorin C

17
Q

Genetic disorders of actin linking to membrane

A

Spherocyic anaemia- mutations in Spectrin, band 4.1 and Ankyrin. Cells are rounder and rupture.

Sickle cell- mutation in B globulin. Low oxygen causes vessel occlusion and ischaemia. Actin oxidation stabilises abnormal cell type and exacerbates phenotype.

18
Q

Structures of cell migration

A

Filopodia- protrude from leading edge, tight actin bundles formed by formins
Lamellipodium- complex of branched actin formed by Arp2/3
Cortical actin cytoskeleton gives stability to membrane
Stress fibres attached to substratum of cell through focal adhesions

19
Q

Membrane extension

A

Leading edge actin is nucleated by Arp2/3 complex, filament grow from + end.
Actin tread milling mediated by cofilin and profilin
Formins and bundling proteins form leading edge

20
Q

Focal adhesions (migration)

A

After membrane extension, plasma membrane attached to substratum. Actin bundles anchored to focal adhesions, stops lamella retracting.
As moves forward, adhesions migrate to the back of the cell and are deassembled

21
Q

Cell body translocation

A

Bulk contents trans located forward

Organelles squeezed forward by cortical contraction of cytoskeleton

22
Q

De adhesion and endocytic recycling

A

Focal adhesions at rear are broken
Integrins are recycled
Freed tail brought forward
Snap forward by stress fibres contracting

23
Q

Control of actin organisation- injury

A

TGF-β released from injury sites and activates Rho

Activated platelets release LPA which activates Rho
RBCs release PDGF (platelet derived growth factor) at site of injury, which activates cdc42 and Rac

24
Q

Activation of Rho

A

GDP form complexed to GDI in inactive form
Activated by GEF which changes GDP to GTP
Causes localisation to membrane
Rho-GTP then binds effectors that cause changes
Binds to RBD of Formin, profilin binds to FH1 allowing addition at FH2
GAP returns it to the cytoplasm

25
Activation of Rac
Activated by CD42 | WAVE -> Arp2/3 -> actin polymerisation -> lamellipodia
26
Activation of cdc42
Activated par6 and WASP Par6-> polarity WASP -> Arp2/3 -> polymerisation -> filopodia formation
27
Wound healing assay
Cells on plate scratched to simulate wound Neighbouring cells sense gap and move Dom negative Rac- needed to activate Arp2/3, lamellipodia not formed well Dom negative Cdc42- do not orientate in right direction as cdc42 needed for polarity Dom negative Rho- failure to establish contractile fibres
28
Role of cdc42 in cancer
Stimulates protease release and invasion by invadopodia Increased cdc42 gene copy number common Leads to active Rac inducing leading edge and high Rho in rear to assemble contractile structures -> myosin II activation
29
3 functional regions of myosin
Head- actin binding region, ATP binding region Neck- a-helical region, regulates head domain Tail- binding sites which determine specificity
30
Myosin superfamily 3 classes
I- membrane association and endocytosis, 1 head II- contraction, 2 heads V- organelle transport, 2 heads and 2 feet
31
Type V myosin in transport
One head binds while the other swings Binds site 72nm ahead Exact distance as helical repeats of the filament Used to segregate organelles
32
Clathrin mediated endocytosis
Assembly of hemispherical clathrin coat Arp2/3 dependent formation of an actin network on the surface of the endocytic coat induced by Las17, Pan1 in yeast Elongation of incipient invagination by Myo-5 actin polymerisation Formation of 2 acto myosin structures which cooperate which yeast amphiphysins in the fission event by generating tension
33
Recycling of endosomes
NMDAR requires myosin Vb which binds RAB11 NMDAR activation -> Ca influx -> myosin Vb activation Translocation of recycling endosomes and cargoes into the spine Transport from endosomes to spine surface mediated by RAB8
34
Myosin in the cell
``` SW2- level arm recovery stroke SW1- cleft closing and actin binding II cell division V- transport vesicles V1- moves backwards along actin X- moves over actin bundles I- organises actin cytoskeleton As neck length increases, velocity increases ```
35
The structure of Tubulin
α-β heterodimer, forms a protofilaments with β at the - end GTP bound to the α subunit is trapped by the β subunit, no exchange or hydrolysis. The GTP in β can be hydrolysed. 13 protofilaments -> sheet -> tube Stabilised cap from GTP bound units. Fast addition at + end.
36
Tubulin in cell division
``` Assembled from MTOCs + ends grow outwards from centrosome Astral point into cytoplasm Kinetochore pull chromatids apart Polar contact each other and slide apart ```