Cytoskeleton I

Question 1

Name 8 functions the cytoskeleton serves?

Answer 1

Spindle fibres during mitosis, cell shape, cell migration and motility, intracellular trafficking, supports membranes, mechanically links adjacent cells, muscle contraction

Question 2

Cytoskeleton supports and protects cell from what?

Answer 2

physical forces

Question 3

Name the 3 filaments the cytoskeleton is made from, from thinnest to thickestt

Answer 3

Actin (microfilaments)
Intermediate filaments
Microtubules

Question 4

Filaments are composed of what?

Answer 4

repeating subunits

Question 5

Describe the structure of actin filaments

Answer 5

Stands in double helix with a positively charged end and negatively charged end

Question 6

what are the actin filaments used for?

Answer 6

maintain cell shape by resisting tensionn (pull)

Question 7

describe the structure of intermediate filaments

Answer 7

Fibers wound into thicker cables, multiple protofilaments which bind laterally to each other

Question 8

describe the structure of microtubules

Answer 8

alpha and beta tubulin dimers form a hollow tube with a positive and negative end

Question 9

Name 6 types of intermediate filaments and where they are located

Answer 9

Keratin - epidermis
Desmin - muscle
Lamins - nucelus 
Vimentin - mesenchymal cells 
Glial Fibrillary Acidc Protein GFAP - Glial cells
Neurofilaments - Neurons

Question 10

What are the main ways in which intermediate filaments differ from the other 2?

Answer 10

Microtubules and microfilaments are more consistent in terms of diameter and composition in euk cells whereas intermediate filaments vary depending on the location of the cell in terms of subunits..
Intermediate filaments are more permanent fixtures, even after removing the other two filaments, the intermiadte filament will retain its shape.

Question 11

Is there polarity in intermediate filaments?

Answer 11

No, each end is identical

Question 12

What allows the intermediate filament to be strong in terms of structure?

Answer 12

The staggered long subunits, which are antiparallel to each other, are twisted into a ropelike structure

Question 13

Actin filaments play what main roles?

Answer 13

Change cell shape, cell locomtion, movemement of organelles inside the cell

Question 14

Actin subunits are called what?

Answer 14

G actin

Question 15

G actin assemble in what way to create what type of filament and give the abbreviation for this

Answer 15

Assemble head to tail creating polar actin filaments, F actin

Question 16

The G acting has a binding site for what?

Answer 16

ATP Binding site

Question 17

What does an actin protofilament comprise of?

Answer 17

Two parallel filaments of actin monomers assembled end to end (plus-end and minus end) which make them polarised

Question 18

Are actin filaments flexible or nah?

Answer 18

Yah

Question 19

Actin filaments are organised into assemblies via what?

Answer 19

Cross linking proteins

Question 20

What affects the type of assembly of actin filaments and what are the 3 types of assembly?

Answer 20

The type of cross linking protein affects the type of assembly.
Meshwork vs bundles vs contractile

Question 21

How are contracticle assemblies formed?

Answer 21

By bundles of F actin forming contractile rings

Question 22

Describe the assembly and what they allow for the following areas in cell

1) stress fiber
2) cell cortex
3) filopodium

Answer 22

1) Contractile and exert tension
2) Gel like network supports the plasma membrane and allows broadextensions of the cell, lamellipodia
3) Tight bundlesin filopodia allow extension

Question 23

What is the cortex?

Answer 23

A network of F actin found beneath the plasma membrane of many cells

Question 24

What regulates the formation of the cortex?

Answer 24

Actin binding proteins

Question 25

What allows for lamellipodia formation

Answer 25

Filamin

Question 26

Spectrin regulates actin meshwork in what?

Answer 26

RBC

Question 27

How do F actins assembly?

Answer 27

Self assembles fromactin subunits so undergoes polymerisation

Question 28

What happens at critical concentration in terms of factin

Answer 28

The rate of subunits ON = rate of subunits OFF

Question 29

What end of F actin grows more rapidly?

Answer 29

Plus end of F actin grows and shortens more rapidly than minus end

Question 30

Actin polymerisation can be used to do what in cells?

Answer 30

Mechanical work in cells

Question 31

if G actin conc is more than the critical conc then what happens? what happens the other way around?

Answer 31

Filament grows when G actin > Cc | and filament shrinks if less

Question 32

F actin growth is controlled how?

Answer 32

By regulating local available G actin

Question 33

What complexes can affect the growth of the f actin and what is the connection between the two

Answer 33

Thymosin and profilin, compete with each other for binding to Gactin

Question 34

What does the thymosin complex do to factin and how?

Answer 34

Thymosin binds G actin and so prevents addition to either the plus or minus end of F actin so it reduces the local G actin at both ends

Question 35

What does profilin do and how in terms of factin?

Answer 35

Profilin binds to G actin and the actin can be added to the plus end but not to the minus end. Increases the local at the plus end

Question 36

F actin growth depends upon balance of what?

Answer 36

Thymosin and Profilin

Question 37

What is the rate limiting step in F actin formation?

Answer 37

Nucleation is a rate limiting step

Question 38

Filament stability and formation depends on what

Answer 38

Depends on the number of H bonds between subunits. Small filament assemblies are unstable Large assemblies are more stable Filament formation depends on formation of nuclei of critical size

Question 39

How can the lag phase/rate limiting step be abolished?

Answer 39

Supply a pre mae nucleus, preformed filament seeds are added to start of with

Question 40

What complex nucleates F actin growth?

Answer 40

ARP complex The inactive ARP complex joins with activating factors and then actin monomers are able to join to the complex to form a nucleated actin filament

Question 41

The ARP complex can promote nucleation from where?

Answer 41

Side of existing actin filament, so its very effective polymerisation results in branching

Question 42

What moves F actin?

Answer 42

Motor protein, Myosin

Question 43

myosin 2 forms what ?

Answer 43

Thick filaments in striated muscle cells

Question 44

What happens during muscle contraction in terms of actin and myosin filaments?

Answer 44

They slide against each other

Question 45

Myosin generates force by coupling what ?

Answer 45

ATP hydrolysis to conformational changes

Question 46

Describe how the power stroke is generated by myosin and actin

Answer 46

The actinf ilament is bound to the myosin head. Binding of ATP to themyosin head then causes the myosin head to detach from the actin filament. Hydrolysis of ATP leads to the formation of ADP and Pi which causes weak binding to the actin filament. The release of Pi increases actin binding andthe release of ADP causes the power stroke