ch16 Flashcards
3 cytoskeletal elements
Microfilaments, Microtubules, Intermediate filaments
Microfilaments
-Actin binds ATP
-forms rigid gels, networks, and linear bundles
-regulated from large # of locations
-highly dynamic, polarized, tracks for myosins
-contractile machinery and network at the cell cortex
Microtubules
-alpha beta tubulin binds GTP
-rigid, not easily bent
-regulated from small # of locations
-highly dynamic, polarized, tracks for kinesins/dyneins
-organization & long-range transport of organelles
Intermediate Filaments
-IF subunits dont bind a nucleotide
-great tensile strength
-pre-existing filaments
-less dynamic, unpolarized, no motors
-cell and tissue integrity
Dynamic Structure
changes in cytoskeleton in signal transduction response
ex. dividing fibroblast
Stable structures
ex. microvilli
dynamic instability
-Microtubules depolymerize 100 times faster when GTP is hydrolyzed.
-Consequently, when the GTP in the cap gets hydrolyzed, the filament undergoes “sudden” or catastrophic shrinkage
Treadmilling
-A polymeric protein filament is maintained at constant length by the addition of protein subunits at one end and loss of subunits at the other
Dynein
-motility and force generation toward the minus ends of microtubules
-associated with microtubules
-from + to - end movement on MT
Kinesin
-regulate microtubule dynamics and length
-associated with microtubules
-from - to + movement on MT
Myosin
-organization & function in muscle cells
-associated with microfilaments
-moves its head groups along the actin filament in the direction of the plus end
Story of muscle contraction
-thin actin & thick myosin: contracts when these slide
-initiated by nerve impulses and calcium ion release
-calcium bounds troponin on actin, exposing myosin bind site
-ADP and P are bound and myosin head releases P, then power stroke, then ATP binds to heads
power stroke
myosin pulling actin inward (toward the M line)
tropomyosin role
stabilizes actin and regulates muscle contraction
troponin role
calcium regulator
