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Flashcards in Cytoskeleton Deck (35)
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1

Definition of cytoskeleton

Network of protein filaments, tubules in cytoplasm, gives shape and coherence

2

Function of cytoskeleton

Connection with ECM
Maintaining cell shape
Intercellular transport
Cytokinesis
Chromosome separation
Cell movement

3

Composition of cytoskeleton

Actin microfilaments
Intermediate filaments
Microtubules

4

Diameter of actin polymers

7-9nm

5

Diameter of tissue specific proteins in intermediate filaments

10nm

6

Diameter of tubulin polyerms

25nm

7

Formation of actin microfilaments

G actin, globular protein has ATP binding domain on left
G actin polymerizes to form F actin (microfilament), involves ATP hydrolysis via non covalent interactions
Forms 2 tightly wound chains

8

Is actin a dynamic structure?

Yes, length depends on the rate of loss and gain of G actin

9

Function of actin

Muscle contraction
Mechanical support (microvilli)
Maintaining cell shape
Cell movement

10

Actin binding proteins

G actin binding proteins
Cross linking proteins
Severing

11

Example of G actin binding proteins

Thymosin B4, inhibits polymerisation

12

Examples of cross linking proteins in actin

Villin, parallel bundles in microvilli
Filamin, joining at angles to create a mesh

13

Examples of severing proteins in actin

Gelsolin, cuts and binds to +ve end, depolymerizes other side

14

Contraction in non muscle cells

Interaction between myosin and actin microfilaments + ATP hydrolysis = movement
Movement within cells
Movement of cells

15

How is actin involved in the movement within cells

Cytokinesis, actin ring forms in cell center, anchors to plasma membrane, myosin contraction constricts cell

16

How is actin involved in the movement of cells

Lamellipodia mediated cell movement across ECM

17

Lamellipodia formation

Extensions of cells have actin network
Generated by rapid growth of actin filaments at cell membrane
Tip of lamellipodia interacts with ECM via integrins
Contraction involving myosin allows cell movement

18

What are intermediate filaments

Polymers of individual IF proteins

19

Types of IF proteins in different cell types

Epithelia, keratin
Axons, neurofilamin
Universal lamins ABC

20

Function of keratin intermediate filaments in epithelia

Physical support, external structures

21

Function of neurofilamin intermediate filaments in axons

Structural arrangement of axons

22

Function of universal lamins ABC intermediate filaments

Support nuclear structure

23

Properties of intermediate filaments

Usually stable, not dynamic
Except lamins, nuclear membrane reforms during mitosis

24

Formation of IF polymers

Monomer
Helical dimer
Dimer + dimer = tetramer
Staggered formation of tetramers, end to end

25

Structure of microtubules

Tubulin monomers, heterodimers of ab tubulin
Protofilament has -ve and + end
Monomers can be added rapidly and removed from +ve, -ve end
13 parallel protofilaments in hollow tube

26

What is the microtubule organizing center (MTOC)

1 end of microtubule attached to MTOC
1 MTOC associated with nucleus
Microtubules grow out from MTOC until destination reached, stabilised

27

Assembly and disassembly of microtubules

Formation:
FTP bound monomers assemble from +ve end

Disassembly:
GTP => GDP + Pi
GDP bound monomers dissociate rapidly

28

Function of microtubules

Dynamic scaffold
Movement of cargo to specific locations in cell
Central internal support of cilia
Stabilize cell structure (platelets)
Organise structure of organelles (ER)

29

Why are microtubules dynamic

Spindle for chromatid separation during mitosis

30

Spindle formation in mitosis and meiosis

Made up of microtubules
Formation initiated from centrosome (type of MTOC)
Centrosomes form at 2 cell poles
Kinetochore microtubules attach to chromatid
Aster microtubules attach centrosome to cell membrane