Page 92 - First Aid for the USMLE Step 1 2020, Thirtieth edition [MedicalBooksVN.com]_Neat

48 SECTION II BIOCHEmISTRY ``BIOCHEMISTRY—CEllUlAR BIOCHEmISTRY ``BIOCHEMISTRY—CEllUlAR

Proteasome Barrel-shaped protein complex that degrades damaged or ubiquitin-tagged proteins. Defects in the
ubiquitin-proteasome system have been implicated in some cases of Parkinson disease.

Cytoskeletal elements A network of protein fibers within the cytoplasm that supports cell structure, cell and organelle
movement, and cell division.
TYPE OF FIlAMENT PREDOMINANT FUNCTION EXAMPlES
Microfilaments Muscle contraction, cytokinesis Actin, microvilli.

Intermediate Maintain cell structure Vimentin, desmin, cytokeratin, lamins, glial
filaments fibrillary acidic protein (GFAP), neurofilaments.

Microtubules Movement, cell division Cilia, flagella, mitotic spindle, axonal trafficking,
centrioles.

Microtubule Cylindrical outer structure composed of a Drugs that act on microtubules (Microtubules
helical array of polymerized heterodimers Get Constructed Very Poorly):
Positive
end (+) of α- and β-tubulin. Each dimer has 2 GTP ƒ Mebendazole (antihelminthic)
Heterodimer bound. Incorporated into flagella, cilia, mitotic ƒ Griseofulvin (antifungal)
spindles. Grows slowly, collapses quickly. ƒ Colchicine (antigout)
Also involved in slow axoplasmic transport in ƒ Vincristine/Vinblastine (anticancer)
neurons. ƒ Paclitaxel (anticancer)
Molecular motor proteins—transport cellular Negative end Near Nucleus.
Protofilament cargo toward opposite ends of microtubule. Positive end Points to Periphery.
ƒ REtrograde to microtubule (+ Ž −)—DYnein.
ƒ Anterograde to microtubule (− Ž +)—Kinesin. REaDY? AttacK!
Negative
end (–) Clostridium tetani, herpes simplex virus,
poliovirus, and rabies virus use dynein for
retrograde transport to the neuronal cell body.

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