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Cytoskeleton Continued


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What is the major subunit of microtubules?
What are the 3 types of cytoskeleton proteins?
Intermediate Filaments - rope-like fibers, assembly regulated by phosphorylation, protect from mechanical stress

Microtubules - hollow cylinders composed of tubulin, originate from MTOC, assembly by GTP hydrolysis, aid in vesicle and organelle movement, axonal transport, cell division, comprise cilia and flagella

Microfilaments - composed of actin, important for cell locomotion and muscle contraction
Where do the forces, that move the cell forward, generated?
What pushes forward the leading edge of a lamellipodium?
-assembly of an actin network

-actin polymerization at this leading edge of the cell pushes the plasma membrane forward and forms new regions of actin cortex
What is the surface that the cell crawls on?
What is the leading edge of the cell called? Describe it.
lamellipodium: sheet-like, contains dense meshwork of actin filaments, oriented so that most of the filaments have their plus ends close to the plasma membrane
What do the focal contacts contain?

(transmembrane proteins in their plasma membrane) adhere to molecules in the extracellular matrix or on te surface of another cell over which the moving cell is crawling
What draws the rear end of the cell forward?
What is the filopodia?
extend from the cell, thin/stiff protrusions both at leading edge and elsewhere on the surface
What is an ARP?
Actin related protein that promotes the formation of branched actin filaments. these proteins form a complex that binds to the existing actin filaments where they nucleate the growth of a new filament which grows out at an angle to form a side branch (formn of 2d actin web). With additional help of actin-binding protens (capping proteins etc) help to push the lamellipodia forward. (mediates nucleation of new actin filaments)
What protects the actin filament plus ends (preventing further assembly or disassembly from old plus ends at the front of the array)?
Capping proteins
Depolymerizing protein?
hydrolysis of ATP bound to polymerized actin subunits promotes depolymerization at the rear end of the actin complex
What are cell locomotion and shape changes important for?
wound healing
What regulates the arrangement of actin filaments?
GTP binding proteins (Rho protein binding family) which affect the arrangement of actin filaments in different ways (Cdc42-triggers actin polymerization and bundling to form the filopodia , Rac GTP-binding protein-promotes formation sheetlike lamellapodia formation)
triggers actin polymerization and bundling to form filopodia
promotes sheetlike lamellapodia formation
What is the motor protein for actin?

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