BIOLOGY 2B03 Lecture Notes - Lecture 16: Phalloidin, Atp Hydrolysis, Keratinocyte
9 Jun 2018
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The Cytoskeleton: Actin
Filaments
3 classes of filaments in eukaryotic cell defined by diameter/type of subunit used as building blocks for filament •
actin filaments labeled using fluorescently-tagged phalloidin molecules •
this is a toxin derived from a ◦
mushroom called the death cap
binds to actin monomers with high ◦
affinity and stabilizes filament when
bound
microtubules labeled with antibody or •
protein fusion such as Tubulin:GFP
intermediate filaments (IFs) labeled •
using antibody specific to monomeric
subunit of filament of GFP-fusion
Cytoplasmic Fibres
each ailment made from smaller protein subunits to •
form long polymer
actin filaments thinnest and comprised of •
monomeric actin subunits
microtubules thickest filaments and made of dimeric •
subunits of alpha and beta-tubulin
3 filaments distributed differently in each cell - in •
epithelial cell:
actin forms ship of microvilli at apical surface ◦
intermediate filaments span cell to provide ◦
structure support
microtubules form networks for intracellular ◦
transport
Actin Structure and Movement
highest density of actin at cell periphery •
actin filaments under cell membrane determines shape and movement of cell •
surface
actin functions include: microvilli, formation of contractile bundles, formation of •
filopodia and contractile ring
actin filaments are two-stranded helical polymers with dimmer of 5-9 nm •
each polymer built from actin monomers called G-actin ◦
actin filaments are polar - both ends look and behave different •
G-Actin
a single actin monomer •
can be divided into 4 domains ◦
large cleft between domains 2 and 4 ◦
cleft forms ATP-nucleotide binding site •
Filamentous Actin (F-Actin)
created through polymerization of actin monomers •
depolymerization and polymerization can occur at •
plus/minus ends, but more growth at plus end and
more shrinkage at minus end
Document Summary
Cytoplasmic fibres each ailment made from smaller protein subunits to form long polymer actin filaments thinnest and comprised of monomeric actin subunits microtubules thickest filaments and made of dimeric subunits of alpha and beta-tubulin. 3 filaments distributed differently in each cell - in epithelial cell: actin forms ship of microvilli at apical surface intermediate filaments span cell to provide structure support microtubules form networks for intracellular transport. G-actin a single actin monomer can be divided into 4 domains large cleft between domains 2 and 4 cleft forms atp-nucleotide binding site. Adp not released because nucleotide-binding site covered in actin filament in cytosol, free actin-adp can release adp and exchange it for atp. Treadmilling when actin filaments with no net increase in length of filament because rate of polymerization at pls end equal to rate of depolymerization at minus-end filament moving forward. Myosin: af-based motor myosin motor proteins able to move along actin filaments and power intracellular cargo trafficking.
