Cytoskeleton

Question 1

Definition of cytoskeleton

Answer 1

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

Question 2

Function of cytoskeleton

Answer 2

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

Question 3

Composition of cytoskeleton

Answer 3

Actin microfilaments
Intermediate filaments
Microtubules

Question 4

Diameter of actin polymers

Answer 4

7-9nm

Question 5

Diameter of tissue specific proteins in intermediate filaments

Answer 5

10nm

Question 6

Diameter of tubulin polyerms

Answer 6

25nm

Question 7

Formation of actin microfilaments

Answer 7

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

Question 8

Is actin a dynamic structure?

Answer 8

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

Question 9

Function of actin

Answer 9

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

Question 10

Actin binding proteins

Answer 10

G actin binding proteins
Cross linking proteins
Severing

Question 11

Example of G actin binding proteins

Answer 11

Thymosin B4, inhibits polymerisation

Question 12

Examples of cross linking proteins in actin

Answer 12

Villin, parallel bundles in microvilli

Filamin, joining at angles to create a mesh

Question 13

Examples of severing proteins in actin

Answer 13

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

Question 14

Contraction in non muscle cells

Answer 14

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

Question 15

How is actin involved in the movement within cells

Answer 15

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

Question 16

How is actin involved in the movement of cells

Answer 16

Lamellipodia mediated cell movement across ECM

Question 17

Lamellipodia formation

Answer 17

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

Question 18

What are intermediate filaments

Answer 18

Polymers of individual IF proteins

Question 19

Types of IF proteins in different cell types

Answer 19

Epithelia, keratin
Axons, neurofilamin
Universal lamins ABC

Question 20

Function of keratin intermediate filaments in epithelia

Answer 20

Physical support, external structures

Question 21

Function of neurofilamin intermediate filaments in axons

Answer 21

Structural arrangement of axons

Question 22

Function of universal lamins ABC intermediate filaments

Answer 22

Support nuclear structure

Question 23

Properties of intermediate filaments

Answer 23

Usually stable, not dynamic

Except lamins, nuclear membrane reforms during mitosis

Question 24

Formation of IF polymers

Answer 24

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

Question 25

Structure of microtubules

Answer 25

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

Question 26

What is the microtubule organizing center (MTOC)

Answer 26

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

Question 27

Assembly and disassembly of microtubules

Answer 27

Formation: FTP bound monomers assemble from +ve end Disassembly: GTP => GDP + Pi GDP bound monomers dissociate rapidly

Question 28

Function of microtubules

Answer 28

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

Question 29

Why are microtubules dynamic

Answer 29

Spindle for chromatid separation during mitosis

Question 30

Spindle formation in mitosis and meiosis

Answer 30

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

Question 31

Movement of cargo within cell

Answer 31

ATP hydrolyses to move cargo along MT Kinesin moves towards +ve => cell periphery Dynein moves towards -ve => nucelus

Question 32

Cilia and microtubules

Answer 32

Supported by MT MTOC called basal body, close to membrane MT facilitates movement of components up and down cilia All cells have single primary cilia, disassembled during mitosis

Question 33

Specialized types of cilia

Answer 33

Stereocilia, sound detection | Motile, respiratory, waft

Question 34

cell-cell junctions, connected to CS

Answer 34

Desmosomes | Gap junctions

Question 35

ECM attachment connected to CS

Answer 35

Hemidesmosomes | Adherens junctions