Cytoskeleton part 1 Flashcards
Function of cytoskeleton
gives shapes able to move or alter shape of cell organisation of organelles transport of organelles cell division chromosome organisation and movement
component - microfilaments
constant flux that lengthen and shorten, disassemble and assemble
component - intermediate filament
made of more stable fibrous protein subunit - slow to break down
component - microtubules - tubulin
lowest in abundance
also made up of subunits that can rapidly assemble and disassemble
actin subunit molecular weight
42000
tubulin subunit molecular weight
50000 for both alpha and beta tubulin
actin unpolymerized form
globular, monomer
tubulin unpolymerized form
globular, dimer
actin - bound nucleotide in unpolymerized state
ATP
1/monomer
tubulin - bound nucleotide in unpolymerized state
GTP
2/dimer
actin - factors required for polymerization
Ca+/Mg2+ in presence of NaCl
tubulin - factors required for polymerization
Mg2+ Chelator to remove Ca2+ NaCl
cause absence of calcium
actin - form of polymer
2 stranded helix - 2 strand wound round each other
tubulin - form of polymer
hollow tube composed of 13 protofilaments
actin - filament diameter
7nm
tubulin - filament diameter
25nm
what is microfilaments made up of
actin monomers - 43kDa in a linear assemlies
formation of microfilaments
4 domain and a central cleft - divalent cation and nucleotide binding site
divergence in actin
variation of actin increasing from amphibia to mammals
actin types - a(sk)
skeletal muscle
a(c)
cardiac muscle
a(sm)
smooth aorta muscles
beta or Y
non-muscles tissue
Y(sm)
smooth stomach muscle
G-actin globular
form of actin
has 1 tightly bound Ca2+
what G-actin contain
non-covalently bound ATP
actin polymerization
G-actin polymerized to form filamentous F-actin
actin filaments have 2 F-actin twisted with 13.5 molecules per repeat - 36nm
ATP during actin polymerization
hydrolysed but energy is not essential
actin depolymerization
F-actin returns to G-actin form
actin monomer shape
per shaped as it has polarity
assembly of actins
has a barbed and pointed end
barbed end
positive
easier for subunits to add to
pointed end
negative
slower to add subunits
cytoskeleton as dynamic structure
able to change quickly
disassembly of cytoskeleton
rapid diffusion of subunits
reassembly of cytoskeleton
filaments at new sites
what microfilament synthesis is controlled by
2 proteins called ArP2 and ArP3
ArP2 and ArP3 function
act as primer for actin polymerization
How microfilament synthesis is initiated
ArP2 and ArP3 bond together - recruiting other protein forming nucleation site
attracting active monomer
binding of ArP2 and ArP3
can cause branching of microfilament network
by binding to existing filaments
profilin and thymosin
regulate rate of microfilament synthesis
controlled by availability of free actin monomers
thymosin function
bind free actin and remove it from pool of actin
profilin function
similar to thymosin
promotes addition of plus end causing rapid growth
gelsolin
bind to pre-existing MF and cleave it off - free filament so new end for addition of free actin subunits
gelsolin regulating MF length
released by PIP2 - free +ve ends for rapid MF elongation
regulation of microfilament association
filamin homodimers crosslink microfilaments forming gel-like network
function of filamin homodimers
form dimer bind to itself at one end and other end bind to MF
villin
similar to gelsolin but not cleave MF
crosslinking therefore bundling
