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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Rim}}
|QuestionAuthor= {{YD}} (Reviewed by Serge Korjian)
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Biochemistry
|MainCategory=Biochemistry
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|MainCategory=Biochemistry
|MainCategory=Biochemistry
|SubCategory=General Principles
|SubCategory=General Principles
|MainCategory=Biochemistry
|MainCategory=Biochemistry
|MainCategory=Biochemistry
|MainCategory=Biochemistry
|MainCategory=Biochemistry
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|MainCategory=Biochemistry
|MainCategory=Biochemistry
|SubCategory=General Principles
|SubCategory=General Principles
|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 towards its positive pole. Which compound in squid axoplasm is responsible for the movement of vesicles?
|Prompt=A researcher is studying the molecular mechanisms of cellular transport. He purifies and salt-washes organelles from squid axoplasm and observes their movement on purified microtubules using video-enhanced microscopy. Initially, the organelles exhibit a nearly undetectable level of movement despite an ATP rich microenvironment. However, addition of a high speed axoplasmic supernatant increases the movement frequency and speed more than 20-fold. The researcher also notices distinct movement of organelles from the negative pole to the positive pole of the microtubules. Which compound in the squid axoplasmic supernatant is responsible for the movement of vesicles?
|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.
|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 organelle transport requires not only ATP as a source of energy but also transport proteins, such as kinesin and dynein. Kinesin is capable of transporting organelles from the negative to positive pole of the microtubule; whereas dynein is capable of transporting organelles from the positive to negative pole. As organelles were initially purified and salt-washed, the transport proteins were lost, and despite an ATP rich microenvironment, no movement occurred. Addition of axoplasmic supernatant that contained the transport proteins led to eventual organelle transport along the microtubule.


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.
|AnswerA=Vimentin
|AnswerA=Vimentin
|AnswerAExp=Vimentin is a type III intermediate filament found in mesenchymal cells.
|AnswerAExp=Vimentin is a type III intermediate filament found in mesenchymal cells.
|AnswerB=Desmin
|AnswerB=Desmin
|AnswerBExp=Desmin is a type III intermediate filament found in muscle cells.  
|AnswerBExp=Desmin is a type III intermediate filament found in muscle cells.
|AnswerC=Dynein
|AnswerC=Dynein
|AnswerCExp=Dynein is a protein that transports organelles from the positive pole to the negative pole of the microtubule.
|AnswerCExp=Dynein is a protein that transports organelles from the positive pole to the negative pole of the microtubule.
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|AnswerE=Plasmin
|AnswerE=Plasmin
|AnswerEExp=Plasmin is a protein that degrades fibrin mesh. It plays a role in the anticoagulation pathway.
|AnswerEExp=Plasmin is a protein that degrades fibrin mesh. It plays a role in the anticoagulation pathway.
|EducationalObjectives=Kinesin helps transport organelles from the (-) to (+) pole of microtubules.
|References=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.
|RightAnswer=D
|RightAnswer=D
|WBRKeyword=kinesin, dynein, transport, protein, proteins, membrane, bound, organelles, microtubule, microtubules, negative, positive, pole, poles
|WBRKeyword=Kinesin, Dynein, Transport, Protein, Proteins, Organelles, Microtubule, Microtubules,  
|Approved=No
|Approved=Yes
}}
}}

Latest revision as of 01:52, 28 October 2020

 
Author [[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Serge Korjian)]]
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. He purifies and salt-washes organelles from squid axoplasm and observes their movement on purified microtubules using video-enhanced microscopy. Initially, the organelles exhibit a nearly undetectable level of movement despite an ATP rich microenvironment. However, addition of a high speed axoplasmic supernatant increases the movement frequency and speed more than 20-fold. The researcher also notices distinct movement of organelles from the negative pole to the positive pole of the microtubules. Which compound in the squid axoplasmic supernatant 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 organelle transport requires not only ATP as a source of energy but also transport proteins, such as kinesin and dynein. Kinesin is capable of transporting organelles from the negative to positive pole of the microtubule; whereas dynein is capable of transporting organelles from the positive to negative pole. As organelles were initially purified and salt-washed, the transport proteins were lost, and despite an ATP rich microenvironment, no movement occurred. Addition of axoplasmic supernatant that contained the transport proteins led to eventual organelle transport along the microtubule.

Educational Objective: Kinesin helps transport organelles from the (-) to (+) pole of microtubules.
References: 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::Yes
Keyword WBRKeyword::Kinesin, WBRKeyword::Dynein, WBRKeyword::Transport, WBRKeyword::Protein, WBRKeyword::Proteins, WBRKeyword::Organelles, WBRKeyword::Microtubule, WBRKeyword::Microtubules
Linked Question Linked::
Order in Linked Questions LinkedOrder::