WBR0847
| Author | [[PageAuthor::Rim Halaby, M.D. [1]]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Biochemistry |
| Sub Category | SubCategory::General Principles |
| Prompt | [[Prompt::A researcher is studying the molecular mechanisms of cellular transport. In his experiment, he purifies tubulin subunits and assembles them into microtubules. Microtubules are stabilized by taxol. Then, he adds ATP and synaptic vesicles and observes that no transport occurs. When he adds squid nerve axoplasm, he notes that vesicles are transported away from the negative pole of the microtubule and towards its positive pole. Which compound in squid axoplasm is responsible for the movement of vesicles?]] |
| Answer A | AnswerA::Vimentin |
| Answer A Explanation | AnswerAExp::Vimentin is a type III intermediate filament found in mesenchymal cells. |
| Answer B | AnswerB::Desmin |
| Answer B Explanation | AnswerBExp::Desmin is a type III intermediate filament found in muscle cells. |
| Answer C | AnswerC::Dynein |
| Answer C Explanation | AnswerCExp::Dynein is a protein that transports organelles from the positive pole to the negative pole of the microtubule. |
| Answer D | AnswerD::Kinesin |
| Answer D Explanation | AnswerDExp::Kinesin is a protein that transports organelles from the negative pole to the positive pole of the microtubule. |
| Answer E | AnswerE::Plasmin |
| Answer E Explanation | AnswerEExp::Plasmin is a protein that degrades fibrin mesh. It plays a role in the anticoagulation pathway. |
| Right Answer | RightAnswer::D |
| Explanation | [[Explanation::Transport of membrane-bound organelles (MBO) along the microtubules requires special proteins that can move organelles, like vesicles, from the positive pole of the microtubule to its negative pole and vice versa. Early experiments that studied the movement of vesicles showed that the addition of both squid axoplasm, which contains transport proteins, and ATP as a source of energy, was required for vesicular transport. Kinesin is capable of transporting organelles from the (-) to (+) pole; whereas dynein is capable of transporting organelles from the (+) to (-) pole.
Educational Objective: Kinesin helps transport organelles from the (-) to (+) pole of microtubules. Reference:
Schroer TA, Schnapp BJ, Reese TS, et al. The role of kinesin and other soluble factors in organelle movement along microtubules. J Cell Biol. 1988; 107:1785-1792. |
| Approved | Approved::No |
| Keyword | WBRKeyword::kinesin, WBRKeyword::dynein, WBRKeyword::transport, WBRKeyword::protein, WBRKeyword::proteins, WBRKeyword::membrane, WBRKeyword::bound, WBRKeyword::organelles, WBRKeyword::microtubule, WBRKeyword::microtubules, WBRKeyword::negative, WBRKeyword::positive, WBRKeyword::pole, WBRKeyword::poles |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |