Cytoskeleton

Question 1

how many polymers are there?

Answer 1

3

-actin filament, microtubules, intermediate filaments

Question 2

what is the function of the cytoskeleton?

Answer 2

structure of cell, intracellular movement of organelles, cell movement

Question 3

is the cytoskeleton dynamic?

Answer 3

• yes

- polymer ⇌ monomer

Question 4

what so accessory proteins regulate?

Answer 4

• site + rate of filament formation
• polymerisation, depolymerisation
• function of cytoskeleton

Question 5

describe the structure of microtubules and their function

Answer 5

• hollow tubes made of tubulin
• rigid, long and straight

-organelle positioning, intracellular transport, cell movement

Question 6

describe the structure of intermediate filaments and their function

Answer 6

• heterogenous groups of filament proteins
• rope like structure

-gives mechanical strength to the cell

Question 7

what is another name for actin filaments?

Answer 7

microfilaments

Question 8

describe the structure of actin filaments and their function

Answer 8

• helical polymers made of actin
• flexible, organised into 20 networks and 3D gas

-cell and organelle shape, cell migration

Question 9

give 2 properties of the polymers that make up the cytoskeleton

Answer 9

• monomers are abundant

- not covalently bonded

Question 10

describe the structure of actin

Answer 10

• twisted chain units of G-actin to form F-actin
• provides structural polarity
• associated w’ actin-binding proteins (ABP)

Question 11

what are the 3 isoforms of actin

Answer 11

• α-actin found in muscle cells

- β and γ actin found in non muscle cells

Question 12

how can actin polymerise?

Answer 12

-by the addition of g-actin to the f-actin

Question 13

how are g-actin levels controlled?

Answer 13

mainly by ABP

• thymosin β4: prevents addition of G-actin
• profilin: facilitates actin polymerisation

Question 14

what are the 2 ABPs that bind to f-actin?

Answer 14

1) actin bundling proteins
- parallel bundles
- eg: microvilli in epithelial cells

2) cross linking proteins
- maintain f actin in gel like network
- eg: cell cortex

Question 15

what do f actin severing proteins do?

Answer 15

break f actin into smaller filaments

Question 16

what do motor proteins do?

Answer 16

transport of vesicles and organelles through filaments

Question 17

how is actin arranged in skeletal muscle?

Answer 17

• para-crystalline array integrated w diff ABPs

- interaction w rosin allows muscle contraction

Question 18

how is actin arranged in non muscle cells

Answer 18

• cell cortex: form a thin cheat beneath plasma membrane

- associated w myosin: form a purse string ring that results in cleavage of mitotic cells (cytokinesis)

Question 19

explain the process of cell migration

Answer 19

• cell pushes out protrusions at its front to show the route
• causes actin polymerisation: the accumulation of f actin

-protrusions adhere to the surface and interns link
filaments to extracellular matrix around cell

-cell contraction and retraction of rear part of the cell

Question 20

describe the structure of intermediate filaments

Answer 20

• toughest of the cytoskeleton filaments
• rope like made of many strands twisted together
• form a network throughout cytoplasm, joining up to cell to cell junctions
• surrounds the nucleus

Question 21

explain the polymerisation of intermediate filaments

Answer 21

• each unit has an N terminal, C terminal globular protein and central elongated ‘ rod-like’ domain
• units for 2 stable dimers
• every 2 dimers form a tetramer
• tetramer bind to each other to make rope like filament

Question 22

what are the two types of intermediate filaments?

Answer 22

nuclear and cytoplasmic

Question 23

what are nuclearlamins?

Answer 23

• nuclear filaments
• forms ‘mesh’ structure
• line inner face of nuclear envelope to strengthen + provide attachment sites for chromatin
• disassemble + reform at each cell division controlled by post translational modifications (de/phosphorylation)

Question 24

what are the cytoplasmic filaments?

Answer 24

• keratins in epithelia
• vimentin in connective tissue, muscle cells and neurological cells
• neurofilaments in nerve cells

Question 25

what do the cytoplasmic filaments do?

Answer 25

• provide tensile strength so cell can withstand mechanical strength
• structural support by creating deformable 3D structural network to reinforce cell shape and organelle localisation

Question 26

describe the structure of microtubules

Answer 26

• hollow tubes makes of ruby lim
• each filament is polarised
• dynamic structure so can assemble and disassemble in response to cell’s needs

Question 27

what are MTOCs?

Answer 27

microtubule organising centres

• specialised protein complexes where assembling of tubulure units start

Question 28

what is the MTOC in most cells?

Answer 28

centrosome

• contains γ tubulim ring that initiated microtubule growth

Question 29

what are the monomers of microtubules?

Answer 29

• α and β tubulin that form heterodimers in a polarised growth

Question 30

what is the function of microtubules?

Answer 30

1) intracellular transport: acts as a railway which molecular motors run different motors for diff cargoes
- directionality of filaments is vital

2) organised position of organelles: provides polarity

3) rhythmic beating of cilia&flagella: motile processes w highly organised microtubule core
- 9+2 structure: axoneme
- bending of cilia & flagella is driven by motor protein dynein
- basal body at base of tubule controls assembly of axoneme