White: Cytoskeleton 1&2 Flashcards
Hereditary spherocytosis and anemia
Diseases caused by defect in RBC cytoskeleton- Spectrin
Cytoskeletal filaments consist of
Multiple protofilaments
Actin filaments
Like mardis gras beads
Determine shape of cells surface and are necessary for whole-cell locomotion, secretion and endocytosis
Microtubules
Slinky of life
Determines the positions of membrane-enclosed organelles
Directs intracellular transport
Make up centrioles and mitotic spindle
Make up cilia and flagella
One end attached to organizing center-centrosome
Intermediate filaments
Girders of life-rope like properties
Strong filament, provides mechanical strength
Resists mechanical stress
Allows formation of hairs and fingernails
Polarity for intestinal cells is maintained by
The cytoskeleton
Microvilli increase surface area by __X
4x
Cytoskeletal polymers are held together by _____ which means what
Weak noncovalent interactions, which means that their assembly and disassembly can occur rapidly
______ are stiff and difficult to bend
______ are flexible and easily bent
Microtubules are stiff and difficult to bend
Actin filaments are flexible and easy to bend
Nucleation
Initial process in polymerization of actin filaments and microtubules
Nucleoside hydrolysis leads to
Treadmilling and dynamic instability
Treadmilling predominates in
Actin filaments
Catastrophe
Change from rapid growth to rapid shrinkage
Rescue
Change from rapid shrinkage to rapid growth
Hydrolysis of GTP changes
Conformation of the subunits, making protofilaments curved, which can then be easily depolymerized
Dynamic instability predominates in
Microtubules
-This is important in separation of chromosomes during mitosis
Intermediate filament formed by
Eight parallel tetramers (protofilaments) packed together laterally
Rate-limiting step in formation of cytoskeletal filament
Nucleation
ARP complex
In presence of activation factor, nucleates actin filament growth from the minus end, allowing elongation at the plus end
- Bypasses rate limiting step of nucleation
- Branches at 70 degree angle
- Used in Listeria
Formin
Nucleates the growth of straight and un-branched actin filaments
Remains associated with rapidly growing plus end as it elongates
Thymosin
Binds actin subunits, preventing assembly into polymer
Profilin
Recruits actin monomers to the actin filament for polymerization
Exposes the site of actin that binds to the plus end
Tropomodulin
Prevents assembly/disassembly at minus end (stabilizes actin filaments) for long lived filament stabilization
Tropomyosin
Stabilizes filament, prevents binding with other proteins
Capping protein
Prevents assembly/disassembly at plus end
Cofilin
Binds ADP-actin, accelerates disassembly
Gelsolin
Severs actin filaments and binds to plus end
Helps with new and rapid assembly or disassembly
Actin is organized into which two types of arrays
Bundle and web-like (gel-like) networks
Alpha-actinin
Bundling protein- cross links actin filaments into loose bundles, allowing myosin II to enter to make actin filaments contractile
Fimbrin
Bundling protein- Cross- links actin filaments into tight bundles, excluding myosin II
Filamin
Promotes the formation of loose, highly viscous gel-like networks by clamping together 2 actin filaments at right angles
Cells require actin gel in order to extend membrane projections
Helps cells to crawl, cannot crawl without filamen
Filamin helps cells
Crawl across a solid surface
Cells require the actin gel in order to extend membrane projections
Spectrin
Attaches cytoskeleton to membrane in RBC
ERM family
Ezrin, Radixin, Moesin
Mediates the attachments b/w actin and plasma membrane
Stathmin
Binds microtubule subunits, preventing assembly
TIPS
The plus end tracking proteins
Remains associated with growing plus ends and can link them to structures such as the membrane
y-TuRC
y-tubulin ring complex
Nucleates assembly and remains associated with minus end
Katanin
Severs microtubules
MAPs
Stabilizes microtubules by binding along sides
XMAP215
Microtubule associated protein that stabilizes plus ends and accelerates assembly
Inhibits switch from growing to shrinking state
Kinesin 13
Enhances catastrophic disassembly at plus end
MAPs have __ domains
2 domains, one that binds microtubule and one that projects outward
Plectin
Cross-linking protein, links microtubules to intermediate filaments
Tau
MAP protein, forms bundles of more closely packed microtubules
Binds microtubule at both its N- and C- termini
Has short projecting loop
MAP2
Long projecting domain
Second microtubule binding domain at other end
Forms bundles of stable microtubules that are kept widely spaced
Cytoplasmic dynein
Vesicle trafficking, localization of the golgi apparatus
Axonemal dynein
Specialized for rapid and efficient sliding movements of microtubule that drive the beating of cilia and flagella
Microtubule nucleation at the centrosome is mediated by
y-tubulin
Actin filaments are nucleated near
The plasma membrane- mediated by ARP complex and formin
