BIOLOGY 2D03 Lecture Notes - Hydrolysis, Neurofilament, Spindle Apparatus
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Cytoskeleton
•Cytoskeleton is made up of 3 dynamic filament systems
oMicrofilaments
Fxn structural, mechanical, support myosin-based contractility
and motility
Actin monomers
One-start left-handed helix or two-start right handed-helix; polar
ATP as energy source
oIntermediate filaments
Fxn Long distance transport, mitotic spindle signaling
Alpha/beta tubulin dimmers, gamma/beta dimmers
11-15 protofilaments form hollow tube, polar
GTP as energy source
oMicrotubules
Fxn structural, mechanical
Lamins, keratins, neurofilament proteins
Coiled-coil dimmers assemble into flexible, nonpolar polymers
No energy source
•Actin
o4 subdomains
o2 start right-handed helix
opolymerizes upon addition of Mg2+, K+, and ATP
orequires nucleation formation of stable trimer
oadditional monomers added w/ nearly identical kinetics
oas monomer pool dimishes, polymer mass reaches steady state
oplus and minus ends have unique critical concentrations
oonce a polymer, the actin rapidly hydrolyzes ATP
oADP-actin released from pointed end
oCritical concentration
Different nucleotide states of the monomers generated during
neucleotide hydrolysis make the ends different
Each end has unique thermodynamic properties
Each end has unique critical concentration for assembly