MCB Lecture 34 Cytoskeleton I Flashcards Preview

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Flashcards in MCB Lecture 34 Cytoskeleton I Deck (43)
0

What are some general functions of the cytoskeleton?

Cell shape
Cell locomotion
Resistance to compressive forces
Movement of organelles within a cell

1

What are the three classes of filament?

Microfilaments / actin
Microtubules
Intermediate filaments

2

What is an example of intermediate filaments?

Keratin, rope like, very strong

3

What are the general features of intermediate filaments?

Very strong and rope like

4

Describe intermediate filament formation

Alpha helix synthesised
Two alpha helices form a coiled coil: dimer
Two dimers interact
Protofilament: four dimers interacting

Many protofilaments line up to form the rope like filament

5

Describe the polarity of intermediate protofilaments

They are non polar, since the protofilaments line up anti parallel

6

What are some general features of actin filaments?

They are flexible

7

Describe the formation of actin filaments

G-actin monomers bind head to tail to form a string
Two strings intertwine to form a protofilament
Many protofilaments are connected by cross-linking proteins

8

Differentiate between F and G-actin

G-actin are the individual subunits

F-actin is the filament formed

9

Describe the polarisation of actin filaments

Since the monomers line up head to tail, the filament is polarised, and has a plus and a minus end

10

What is the function of cross linking proteins inaction filaments?

Forms the assemblies of actin filaments

11

Describe the function of contractile belts, and which type of cytoskeleton filaments is involved

The contractile belts carry out epithelial folding
Actin and Adherens junctions are involved

12

Describe the function of migratory processes, and which cytoskeletal filaments are involved

Migratory processes extend out so that the cell can move
Actin is involved

13

What is the function of the cell cortex?
What are some of the proteins involved?

The cell cortex forms the broad protrusions during cell locomotion (lamellipodium)

Filamin
Spectrin

14

What is Filamin?

This is a protein that binds to actin filaments in the cell cortex.
It allows lamellipodium formation

15

What is Spectrin?

This is a protein that binds to actin filaments in RBC, regulating mesh work

16

What is a lamellipodium? Compare with a Filopodium

This is the broad protrusion, actin is more disordered

Filopodia are smaller protrusions with ordered bundles of actin

17

Under what conditions will actin polymerisation occur?

Kon > Cc

The concentration of subunits is greater than the critical concentration

18

Under what conditions will actin depolarisation occur?

Koff < Cc

The concentration of subunits falls below the critical concentration.
The whole filament then disassembles

19

Describe the function of the plus end

Monomers are added and removed more rapidly from this end

20

Which two proteins regulate the polymerisation and depolymerisation of F-actin?

Thymosin
Profilin

21

What is the function of thymosin?

It binds to G-actin, stopping it from binding to the plus and minus ends of the F-actin

It effectively reduces the substrate concentration

22

What is the function of profilin?

It binds to G-actin subunits, allowing for their rapid addition to the plus end of F-actin

It effectively increases the concentration of actin subunits, increasing the rate of polymerisation

23

What is nucleation?

This is the formation of a stable nucleus, so that polymerisation can occur

24

What is the rate limiting step in F-actin polymerisation?

Nucleation

25

Describe how the rate limiting step of actin polymerisation may be overcome

By adding a preformed nucleus of actin monomers, we don't wait for it to spontaneously happen, which is very rare and thus slow

26

Describe the function of the ARP complex

The ARP complex, when activated, binds actin monomers and allows for rapid poly erasion of F-actin

27

Describe broadly how remodelling of F-actin occurs

There are 100s of proteins that stabilise, promote or inhibit polymerisation, promote or inhibit depolymerisation etc.

28

What is the classification of motor proteins? How do they relate to the cytoskeleton?

They are proteins, not cytoskeletal elements.
They are relevant because they interact with actin filaments and microtubule tracts

29

Describe the myosin family

There are many, many types

30

What is the function of myosin?

It moves actin filaments (in muscle contraction)

31

Describe how myosin interacts with actin in muscle contraction

1. ATP binds, and the head dissociates from actin
2. ATP is hydrolysed, head cocks and it binds to actin
3. Dissociation of the phosphate triggers the power stroke
4. ADP dissociates during the power stroke

32

Describe the presence of actin within a motile cell (3)

1. Filopodia
Very ordered, tight parallel bundle
2. Cell cortex
Looser arrangement, gel like network with Filamin protein
3. Stress fibres
Contractile bundle

33

Differentiate between the ways that actin and microtubules area polymerised and stabilised

Actin:
- Arp Allows for network of actin filaments by attaching to filaments
- thymosin
- profilin

Microtubules
- GTP cap: binds to the beta (+) and allows for rapid polymerisation, loss of which causes a catastrophe
- MAP: binds to GTP cap on beta end and stabilises the microtubule

34

Differentiate between the nucleation of actin and microtubules

Actin:
- ARP complex nucleates actin

Microtubules:
- Gamma-Tubulin- ring complex: nucleation of microtubules, found in controsome

35

What are the three type of actin assemblies?

Contractile, mesh work, bundle

36

Where are actin bundle seen?

Filopodia extensions
Contractile ring

37

Which motor protein is highly involved in cell locomotion?
Specifically, which phase of cell locomotion?

Myosin
In the traction phase

38

Which protein complex is really important in protrusion during cell locomotion?

The arp complex

39

Desmin
Lamin
Vilmentin
Glial fibrillary acidic protein and
Neurofilament are all examples of what?

Intermediate filament

40

Profilin competes with ... For binding to ..., promoting ...

Thymosin
Actin monomers (G actin)
Promoting actin filament polymerisation

41

What is the structure of the monomer that makes up microtubule protofilaments?

It is a Tubulin heterodimer: the two bits making up the dimer are different

42

What is the role of microtubules in the secretory pathway?

It provides a track along which the vesicles move from the ER to the Golgi, then to the plasma membrane

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