GRE Subject Test: Biochemistry, Cell, and Molecular Biology : Help with Nuclear Transport

Study concepts, example questions & explanations for GRE Subject Test: Biochemistry, Cell, and Molecular Biology

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Example Questions

Example Question #1 : Help With Nuclear Transport

What is the function of RanGAP in relation to nuclear import and export?

Possible Answers:

Bind importins/exportins and bring them through the nuclear pore complex

Attach GTP to Ran

Bind cargo proteins

Maintain a gradient of GTP/GDP bound Ran 

Correct answer:

Maintain a gradient of GTP/GDP bound Ran 

Explanation:

RanGAP is notable for its ability to activate the GTPase function of the Ran protein. This allows for the hydrolysis of the third phosphate of GTP-bound Ran and the maintenance of a Ran-GDP/Ran-GTP gradient that is used to control nuclear import and export. RanGAP does not directly associate with cargo proteins or importins/exportins.

Example Question #2 : Help With Nuclear Transport

Which of the following choices would have the biggest effect on nuclear transport?

Possible Answers:

A non-functional copy of the gene that encodes CRM1

An inhibitor that globally targets exportins at their cargo binding sites

An inhibitor that globally targets importins at their cargo binding sites

A mutated, non-functional copy of RanGAP

Correct answer:

A mutated, non-functional copy of RanGAP

Explanation:

Because the question is asking which will have the largest effect, it makes sense that the answer should affect import and export globally.

Importins and exportins only work in one direction. While mutations to either of these protein classes would greatly affect nuclear transport, each is only responsible for "half" or the transport across the membrane. CRM1 is a well characterized exportin.

RanGAP, however, is responsible for helping maintain the gradient of Ran bound to GTP or GDP. The gradient of RanGTP/GDP is what provides global directionality to nuclear import and export. Loss of RanGAP would affect both import and export, having the largest detrimental effect on nuclear transport.

All GRE Subject Test: Biochemistry, Cell, and Molecular Biology Resources

1 Diagnostic Test 201 Practice Tests Question of the Day Flashcards Learn by Concept
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