Cytoskeleton part 1

Question 1

Function of cytoskeleton

Answer 1

gives shapes
able to move or alter shape of cell
organisation of organelles
transport of organelles
cell division
chromosome organisation and movement

Question 2

component - microfilaments

Answer 2

constant flux that lengthen and shorten, disassemble and assemble

Question 3

component - intermediate filament

Answer 3

made of more stable fibrous protein subunit - slow to break down

Question 4

component - microtubules - tubulin

Answer 4

lowest in abundance

also made up of subunits that can rapidly assemble and disassemble

Question 5

actin subunit molecular weight

Answer 5

42000

Question 6

tubulin subunit molecular weight

Answer 6

50000 for both alpha and beta tubulin

Question 7

actin unpolymerized form

Answer 7

globular, monomer

Question 8

tubulin unpolymerized form

Answer 8

globular, dimer

Question 9

actin - bound nucleotide in unpolymerized state

Answer 9

ATP

1/monomer

Question 10

tubulin - bound nucleotide in unpolymerized state

Answer 10

GTP

2/dimer

Question 11

actin - factors required for polymerization

Answer 11

Ca+/Mg2+ in presence of NaCl

Question 12

tubulin - factors required for polymerization

Answer 12

Mg2+ Chelator to remove Ca2+ NaCl

cause absence of calcium

Question 13

actin - form of polymer

Answer 13

2 stranded helix - 2 strand wound round each other

Question 14

tubulin - form of polymer

Answer 14

hollow tube composed of 13 protofilaments

Question 15

actin - filament diameter

Answer 15

7nm

Question 16

tubulin - filament diameter

Answer 16

25nm

Question 17

what is microfilaments made up of

Answer 17

actin monomers - 43kDa in a linear assemlies

Question 18

formation of microfilaments

Answer 18

4 domain and a central cleft - divalent cation and nucleotide binding site

Question 19

divergence in actin

Answer 19

variation of actin increasing from amphibia to mammals

Question 20

actin types - a(sk)

Answer 20

skeletal muscle

Question 21

a(c)

Answer 21

cardiac muscle

Question 22

a(sm)

Answer 22

smooth aorta muscles

Question 23

beta or Y

Answer 23

non-muscles tissue

Question 24

Y(sm)

Answer 24

smooth stomach muscle

Question 25

G-actin globular

Answer 25

form of actin | has 1 tightly bound Ca2+

Question 26

what G-actin contain

Answer 26

non-covalently bound ATP

Question 27

actin polymerization

Answer 27

G-actin polymerized to form filamentous F-actin | actin filaments have 2 F-actin twisted with 13.5 molecules per repeat - 36nm

Question 28

ATP during actin polymerization

Answer 28

hydrolysed but energy is not essential

Question 29

actin depolymerization

Answer 29

F-actin returns to G-actin form

Question 30

actin monomer shape

Answer 30

per shaped as it has polarity

Question 31

assembly of actins

Answer 31

has a barbed and pointed end

Question 32

barbed end

Answer 32

positive | easier for subunits to add to

Question 33

pointed end

Answer 33

negative | slower to add subunits

Question 34

cytoskeleton as dynamic structure

Answer 34

able to change quickly

Question 35

disassembly of cytoskeleton

Answer 35

rapid diffusion of subunits

Question 36

reassembly of cytoskeleton

Answer 36

filaments at new sites

Question 37

what microfilament synthesis is controlled by

Answer 37

2 proteins called ArP2 and ArP3

Question 38

ArP2 and ArP3 function

Answer 38

act as primer for actin polymerization

Question 39

How microfilament synthesis is initiated

Answer 39

ArP2 and ArP3 bond together - recruiting other protein forming nucleation site attracting active monomer

Question 40

binding of ArP2 and ArP3

Answer 40

can cause branching of microfilament network | by binding to existing filaments

Question 41

profilin and thymosin

Answer 41

regulate rate of microfilament synthesis | controlled by availability of free actin monomers

Question 42

thymosin function

Answer 42

bind free actin and remove it from pool of actin

Question 43

profilin function

Answer 43

similar to thymosin | promotes addition of plus end causing rapid growth

Question 44

gelsolin

Answer 44

bind to pre-existing MF and cleave it off - free filament so new end for addition of free actin subunits

Question 45

gelsolin regulating MF length

Answer 45

released by PIP2 - free +ve ends for rapid MF elongation

Question 46

regulation of microfilament association

Answer 46

filamin homodimers crosslink microfilaments forming gel-like network

Question 47

function of filamin homodimers

Answer 47

form dimer bind to itself at one end and other end bind to MF

Question 48

villin

Answer 48

similar to gelsolin but not cleave MF | crosslinking therefore bundling