Cytoskeletal Motility Flashcards
Types of Intermediate Fillaments
Keratin, Vimentin, Neurofilaments
Where is Keratin Expressed
Epithelial Cells
IF provide?
tensile strenght and allow cells to withstand mechanical strength
Which of Cytoskeletal Elements are toughest?
Intermediate Filaments
Vimentin
Found in mesenchymal Cells
Associate with microtubules via accessory proteins
Maintain cell organizanization
Neurofilaments
Fill the core of neuronla axons
Lamins
Line and strengthen the inside surface of the INNER nuclear membrane
Nuclear Lamina
Disassembles and re-forms at each cell division
Phosphorylation Weakens the binding between the tetramers and causes the filaments to fall apart
Dephosphorylation at end of mitosis causes the lamins to reasemble
Intermediate Dependent molecular motors
DO NOT EXIST
Cross Links of IF to MT
Caused by Plectin
IF found in
Desomosomes
Microtubules
Long and relatively stiff HOLLOW tubes of protein that can rapidly dissassemble in one location and resasemble in another
Has Polarity: is essential to provide a track for directed movement
Microtubules Structure
tubulin: a dimer of two similar globular proteins
alpha and beta tubulin
tubulin has 13 tubulin protofilaments
each protofilament has a + and - end
Dynamic Instability
Microtubules innate ability to disassembe and reassemble
Comes from intrinsic capcity of tubulin molecules to hydrolyze GTP
Tubulin with GTP pack tightly
Tubulin with GDP doesn’t pack tightly
Colchicine
Binds tightly to free tubulin and prevents its polymerization of microtubules
Taxol
tightly binds to microtubules and prevents them from losing subunits
Lock in GTP conformation
Microtubules can grow, but cannot shrink
Method of Microtubule Growth
Like a fisherman casting out reel
Motor Proteins
Kinesins, Dyneins, Myosin
ATP-binding heads and tails
Heads have ATPase
Exhibit Polar Motility
Kinesins:
Motor proteins that move along microtubules to the + end
Dyneins
Motor proteins that move along microtubules to the -end
Microtubules Built From…..
Direct growth from Centriole or
Growth from gamma tubulin ring
Microtubule Associated Proteins
Promote asembly and stabilize microtubules
Define Microtubule spacing within cell processes
Cilia
Hairlike Structure ~0.25 um that move fluid over the surface of a cell or to propel a single cell through a fluid
Flagella
used for locomotion and do not have sweeping motion but whip like
Arranged in nine double microtubules in a ring aorund a pair of single microtubules (9+2)
Nexin attaches microtubules so that ATP binding causes sliding rather than bending
Actin
inherent polarity, rarely occur in isolation in the cell; generally found in cross-linked bundles and networks
Growint actin filament
Use ATP, once ATP is hydrolyzed to ADP, actin monomer is less stable and reduces the strength of the binding between monomers
Cytochalasin & Phalloidin
Inhibits actin polymerization
Thymosin & profilin
Prevent Free actin monomers from polymerizing
Actin Related Proteins
Allow for Branching
Control of Actin
Actin arrays controlled by Rho GTPases (Rac, Rho, CDC42)
Myosin and Kinesin are related to Ras GTPase
Polarity of Kinesin Family Motors
N-Terminal motor = + End Directed
C-Terminal Motor = - End Directed
Internal Motor = MT depolymerizing Activity
Myosin
Moves vessicle towards + End
Dynein Involved In
Mitosis, Nuclear Envelope Breakdown, vesicle/particel transport, golgi maintenance
Dynein
Moves vessicle towards - End
Dynactin
Adaptor protein that binds cytoplasmic dynein to vesicles
