Cytoskeleton Lec 1 Flashcards
(47 cards)
1
Q
Functions of the cytoskeleton…
A
- membrane trafficking
- support
- cytokinesis
- muscle contraction
- formation of axons and dendrites
- sperm to swim
- shape
- growth of plant cell
2
Q
Microtubules subunit is…
A
Tubulin
3
Q
What are the three types of Cytoskeletal Filaments and their diameters?
A
Intermediate Filaments - 10nm
Microtubules - 25nm
Actin Filaments - 7nm
4
Q
Role of intermediate filaments
A
- Provide tensile strength for cells
- mechanical strength
- highly abundant in cells
- network through cytoplasm and nucleus to give shape
5
Q
4 types of intermediate filaments
A
- Keratin in epithelial cells
- Vimentin and vimentin related filaments in connective tissue, muscle cells of the nervous system.
- Neurofilaments in nerve cells.
- Nuclear lamins found under nuclear envelope to give nucleus its shape.
6
Q
The construction of Intermediate Filament
A
- protein with globular N & C terminus
- long alpha helix stretch in between two domains
- 48nm long, 320 amino acids long
7
Q
Why are intermediate filaments so strong?
A
- associate with one another by helix coiling around another helix, lots of surface contact
8
Q
How do the Intermediate filaments ‘build up’?
A
- Have association of the dimers to form a staggered tetramer
- One N of one with C of other dimer pair.
- can build up higher order structures with this type of association
9
Q
What consists of the rope which makes up a full intermediate filament?
A
- 8 structures twisted in to a rope of diameter 10nm approx
10
Q
Keratin Features
A
- Attached to plasma membrane in junctional complexes.
- Spam the interior of ep cells, intermediate filaments span width of cells, and contact another junction on another neighbouring cell, attached to plaque proteins
11
Q
Plaque proteins features and use.
A
- Plaque proteins ( which are attached to keratin) are attached to integral membrane proteins
12
Q
Cadherin proteins features and uses.
A
- make contact with the cadherins in the other cell (junction) the two cells held together by cadherins interacting with one another.
- intermediate cells not directly in contact , indirectly held together.
13
Q
Diseases associated with intermediate filaments
A
- struggle in forming junctions on epithelial cells - can lead to disease called epidermolysis
- rare/serious
- skin susceptible to mechanical injury, fragile.
14
Q
What does a healthy network of intermediate filaments enable?
A
-the skin and epithelial tissues can be stretched and you wont get a rupture of the barrier.
15
Q
Intermediate filaments do/don’t have polarity?
A
DON’T
16
Q
Features and roles of Actin Filaments
A
- Found in all eukaryotes
- smallest
- made up of small globular proteins which associate with each other
- unstable without associated proteins
- some stable actin filaments in muscle cells
- dynamic and changing constantly
17
Q
Nomenclature of Actin Filaments
A
- Monomer of actin is called G actin
- Associates with other monomers to form filament its called F actin
18
Q
Stages and conditions of in vitro test tube actin filament formation
A
- G actin in tube, add ATP, and salts MG2+ and K+
- G actin forms filaments as long as conc of actin is high enough.
19
Q
What is the critical concentration?
A
- Conc above which actin will start to add subunits to filaments
- below this actin will get shorter (in vitro) above this actin fil will get longer (in vitro)
20
Q
Actin monomer features
A
- globular protein
- two lobes
- deep clef where ATP sits
- when monomers associate, they associate a bit staggered so you get a slight spiral of the filament.
21
Q
How to distinguish between the actin terminals
A
- one minus end where ATP binding clef exposed
- one plus end where dome of the actin monomer exposed
22
Q
Do actin filaments have polarity?
A
YES
23
Q
What sorts of proteins bind to actin?
A
- monomer binding proteins
- nucleating proteins
- cross linking proteins
- capping proteins
- bundling proteins
- motor proteins
24
Q
How is actin filament production regulated?
A
- SMALL GTPASES regulate
- MONOMER SEQ PROTEINS – (Thynosine, prevents actin monomers binding, provonin encourage)
- Cross linking proteins, get network of filaments
- Side binding proteins which stabilise to prevent them dissociating
25
What is the role of Motor Binding proteins?
- move along actin filaments as actin have a directionality about them.
26
Drugs that you can treat actin with which effect it...
- Cytochalasin D binds to the + end of F-actin and prevents further addition of G-actin
- Phalloidin from the poisonous mushroom amonita, binds F-actin and prevents actin filaments from depolymerising
27
Role of actin...
Actin gives mechanical strength and cell shape
- cell crawling
- muscle contraction and organelle movement
28
Cell crawling extension names and shape... (actin)
- extensions called filapodia (finger like projections) or lammelipodia (sheet like projections)
- form projections where there are nucleating projections on membrane so you send out membrane projections and get formation of actin below the plasma membrane.
29
How do cells move directionally along substrate in actin?
Control of this is by Ro and Rack GTPases.
30
What are motor proteins?
- actin dependent motor proteins belong to the myosin family of proteins
- myosin can bind and hydrolyze ATP
- provides energy for their movement along actin filament from the minus end towards the plus end
31
How do organelles move?
- coordinated movement of myosins attached to cellular organelles can move organelles along actin filaments
32
Muscle contractions
- filaments do not shorten
- move relative to one another
- myosin heads walk towards the plus ends of actin filaments
- pulling the z discs closer together
33
What are microtubules?
- long hollow cylinders
- tubulin monomers
- 25nm diameter
- rigid straight structures
- grow out from microtubule organising cells (MTOC)
- have polarity
34
The assembly of microtubules
- tubulin made up of an alpha and beta dimer
- stack together to form a hollow cylindrical tubule
- appears as a cylinder made up of 13 protofilaments
- add subunits around base of tower to build up
35
Hydrolysation of microtubules
- GTP never gets hydrolysed
- GTP bound to beta tubulin can however be hydrolysed
- beta tubulin exposed at + end
- alpha at - end of tubule
36
Assembly and disassembly of microtubules to maintain balance
- lots of microtubule is unstable - allows them to under go remodelling
- usually grow from a microtubule organising centre (centrosome)
37
How many protofilaments is the cylinder made up of?
13
38
Which molecule never gets hydrolysed in tubulin molecule?
GTP bound to beta tubulin
39
where is centrosome located?
- in the cytoplasm just outside the nucleus
40
What is the centrosome made up of?
- centrioles built up from a cylindrical array of 9 microtubules each with 2 partial microtubules attached
- amorphous structure of proteins
41
Where are microtubules nucleated from?
the centre of the cell
42
How is GTP hydrolysis thought to control growth of microtubules?
- new dimer units added to tower quicker than gtp is hydrolysed
- new subunits with gtp bound being added
- microtubule will keep adding subunits so growth of MT
- GTP hydrolysis soon after incorporation of sub units
43
What is dynamic instability?
- Rapid growth with GTP - capped end
- accidental loss of GTP cap
- rapid shrinkage
- regain of GTP cap
- Rapid growth with GTP capped end
44
What does GTP hydrolysis do regarding the bonds in the microtubule?
GTP hydrolysis changes subunit conformation weakening bonds in the microtubule.
45
At any one given time due to the instability of microtubules, what is the growth of microtubules?
- some always grow
| - some always shrink
46
How are MT stabilised?
- by interacting proteins
47
What are the functions of microtubules?
- cellular organisation
