Cytoskeleton Filaments

Question 1

Name the 3 major filaments in cytoskeleton

Answer 1

Intermediate filaments
Microtubules
Actin filaments

Question 2

What are the major functions of the cytoskeletal filaments

Answer 2

Facilitate cell movement and also maintain shape

Question 3

Where are intermediate filaments located

Answer 3

Cytoplasm and nucleus

Question 4

What are cells/intermediate filaments linked by

Answer 4

Desmosomes (proteins)

Question 5

What are intermediate filaments called when in nucleus and what is their job in nucleus

Answer 5

Nuclear lamins

Form mesh along inner membrane to act as anchors for chromosomes and pores

Question 6

Explain the structure of IF from monomer to tetramer

Answer 6

A- helical monomer which forms a coiled dimer when 2 helixes

Then the tetramer means 4 A helical strand (2 coiled dimers)

Question 7

What is assembly and disassembly of IF regulated by

Answer 7

Phosphorylation (ATP)

Question 8

What are the subunits called which make up the nuclear lamins

Answer 8

Lmna Lmnb LmnC

Question 9

What happens to IF in cell division

Answer 9

Phosphorylated to segregate the nucleus

Question 10

The protein domains of IF differ between each area /cell of body

Eg keratin, neueofilaments, nucleus

What does this allow

Answer 10

Determination of source of tumours

Question 11

Where are microtubules found and what’s their role

Answer 11

Cytoplasm (grow from centromere)

Function is division of chromosomes
Shuttling of vesicles in cytosol
Facilitate cilia movement

Question 12

What are the monomers of microtubules called and how are they built up

Answer 12

Tubulin monomers

Built and dissembled by GTP

Question 13

Why are microtubules found in ciliated cells extending from basal body?

Answer 13

They facilitate cilia movement

Question 14

Explain the full structure of microtubules

Answer 14

Made of tubulin heterodimers which include both Beta and Alpha

Tubulins form protofilaments

There are 13 protofilaments giving the tube like structure

They have a plus end (beta) and a negative (alpha)

Question 15

What does it mean that microtubules have polarity

Answer 15

The plus end is Beta groups

The minus end is alpha - this is where they break down

Question 16

What are the 2 motor proteins found attached to microtubules to carry cargo?

Answer 16

Dynein

Kinesin

Question 17

What do kinesin and Dynein motor proteins use to move across microtubules

Answer 17

Atp hydrolysis (when atp is bound to their globular heads)

Question 18

Which end does dynein and kinesin move cargo to

Answer 18

Dynein = minus

Kinesin = plus end

Question 19

What does the cargo carried depend on for dynein and kinesin

Answer 19

Their tail shape

Question 20

How are cilia arranged (in terms of microtubules and dynein)

Answer 20

9 doublets (a,b microtubules) 
2 singlets joined by nexins 

Moved by dynein arms

Question 21

What if nexins didn’t join singlets

Answer 21

Dynein would cause sliding in the tubules and wouldn’t be able to bend

Question 22

What is actins job

Answer 22

Cell contraction and preventing too much stretch
Cell movement
Keep microvilli upright

Question 23

Explain actin filaments structure

Answer 23

2 stranded helix which is coiled

37nm

Question 24

What do actin filaments use to build/disassemble

Answer 24

ATP hydrolysis (phosphorylation)

Question 25

Why is actin found in microvilli

Answer 25

Keeps the microvilli upright

Question 26

When actin is in high concentrations in cytoplasm what do they form

Answer 26

Cross linked bundles

Question 27

Actin is polar because it has a - end and a + end. Why does the + end grow rapidly

Answer 27

Due to Globular actin monomers

Question 28

There are 6 actin binding proteins. Name them

Answer 28

``` Myosin motor proteins Bundling proteins Severing proteins Cross linking proteins Side binding proteins ```

Question 29

What do severing proteins do to actin filaments

Answer 29

They fragment them to form a fluid state

Question 30

What do bundling proteins do

Answer 30

Hold actin filaments in a gel mesh network in the cortex for example for microvilli support

Question 31

What do myosin motor proteins do

Answer 31

Form contractile bundles with actin

Question 32

Actin filaments cause cells to move across surfaces. First step is protrusion explain it

Answer 32

Actin polymerisation at the + end pushes the membrane of the cell forward Forms protrusion (new actin cortex)

Question 33

Explain the next step after protrusion of cellular movement

Answer 33

New Anchorage points form at the new actin cortex (protrusion) which allows movement across the cell Contraction of myosin motor proteins at the end of the cell pushes it forward

Question 34

What are myosins and what is their job

Answer 34

Motor proteins which move vesicles or membrane via their tails Globular heads which use ATP hydrolysis to move are attached to actin filaments

Question 35

Which type of myosin moves membranes and vesicles?

Answer 35

Myosin I

Question 36

What does myosin II do

Answer 36

It slides actin filaments past one another using the globular heads in muscle contraction

Question 37

Spectrin is another cytoskeleton protein in inner membrane of cells. Explain the structure and function

Answer 37

Tetramer of spectrin is bound to actin molecules in a pentagon structure This allows stability and cell shape to be maintained

Question 38

What 2 reasons are there actin associated proteins

Answer 38

For regulation / polymerisation For movement - eg Motor myosins

Question 39

Name the 4 types of intermediate filaments and where found

Answer 39

Nuclear lamins Keratins filaments (eg in skin,nails) Vimentin- muscle Neurofilaments- in neurones

Question 39

What is keratins IF job

Answer 39

Found in cytoplasm of cells stuck to desmosomes and prevent excess stretching and rupturing of cells

Question 39

What is IF job in neurofilaments (neurones)

Answer 39

Determine axon diameter and provide neurone strength

Question 40

What is IF job in vimentin (muscle)

Answer 40

Lines the sarcomere and prevents muscle fibre misalignment

Question 41

What is an example of where bundling proteins bundle actin together

Answer 41

Microvilli support

Question 42

Where is cross linking protein action found in actin

Answer 42

In spectrin network in RBCS