Actin/Cytoplasmic Filaments and Cell Motility Flashcards
Microtubule functions
Transport
Organelle arrangement
Mitosis
Cilia & flagellar movement
Microfilament functions
Muscle contraction
Cell adhesion & motility
Microvilli
Smallest but most common
Functions of intermediate filaments
Mechanical integrity
Motility
Scaffolds
Duchenne Muscular Dystrophy
- X-linked mutation –> complete absence of dystrophin –> plasma membrane of muscle cells tears during contraction
- Progressive
- Walking on toes; protruding abdomen; shoulder & arms held back; weakness and muscle wasting
Dystrophin
Links actin to the extracellular matrix by bindin a,B dystroglycan on the plasma membrane, which binds laminin*, perlecan, and agrin in the ECM
Becker’s muscular dystrophy
Lower expression levels of dystrophin; less severe w/later age of onset than DMD
Why do people with DMD have enlarged calves?
Damaged muscle tissue –> fibroblasts migrate there to replace destroyed muscle with collagen and scar tissue
How does ATP control the formation of actin filaments?
ATP-G-actin is added more quickly to the + end, and polymerization activates the intrinsic ATPase activity of actin –> hydrolysis and dissociation of ADP+Pi makes the actin less stable such that it falls off at the - end
What binds to ATP-G-actin and sequesters it from polymerization?
Thymosin B4 and profilin
The (+) end of F-actin as a ___er critical concentration for ATP-G-actin, which is why it’s added more efficiently at the (+) end
lower critical concentration
Cofilin
Binds F-actin subunits with ADP and breaks it into shorter pieces –> more (-) ends for disassembly
Profilin
Enhances exchange of ADP for ATP on free G-actins –> regenerates more ATP-G-actin but also sequesters it
Thymosin B4
Binds ATP-G-actin to sequester it form polymerization until there’s too little
Maintains a steady state level of F-actin
Tropomodulin
Binds at the (-) end to stabilize F actin
CapZ
Binds at the (+) end to prevent further polymerization
Controlled by signal transduction molecules and other regulatory proteins