WBR0979

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Biochemistry
Sub Category	SubCategory::General Principles
Prompt	[[Prompt::Shown below is a diagram depicting the sorbitol metabolism. Which of the following correspond to the cofactors X and Y respectively? ]]
Answer A	AnswerA::NADPH and NAD+
Answer A Explanation	AnswerAExp::NADPH and NAD+ are the correct cofactors corresponding to X and Y respectively.
Answer B	AnswerB::NAD+ and NADPH
Answer B Explanation	AnswerBExp::This answer is incorrect. NADPH and NAD+ are the correct cofactors corresponding to X and Y respectively.
Answer C	AnswerC::ATP and NAD+
Answer C Explanation	AnswerCExp::This answer is incorrect. NADPH and NAD+ are the correct cofactors corresponding to X and Y respectively.
Answer D	AnswerD::NADPH and ADP
Answer D Explanation	AnswerDExp::This answer is incorrect. NADPH and NAD+ are the correct cofactors corresponding to X and Y respectively.
Answer E	AnswerE::NAD+ and ATP
Answer E Explanation	AnswerEExp::This answer is incorrect. NADPH and NAD+ are the correct cofactors corresponding to X and Y respectively.
Right Answer	RightAnswer::A
Explanation	[[Explanation::NADPH is the reduced form of NADP+ and NAD+ is the oxidized form of NADH. These cofactors play a role as electon carriers and donors in redox reactions. Glucose is converted to sorbitol under the action of aldose reductase which requires NADPH as a cofactor. Sorbitol is converted to fructose under the action of orbitol dehydrogenase which requires NAD+. Shown below is a diagram depicting the metabolism of sorbitol. File:Sorbitol pathway.png Educational objective: Glucose is converted to sorbitol under the action of aldose reductase which requires NADPH as a cofactor. Sorbitol is converted to fructose under the action of sorbitol dehydrogenase which requires NAD+. Reference: First aid for USMLE step 1, 2013. Page 104. Educational Objective: References: ]]
Approved	Approved::No
Keyword	WBRKeyword::NADPH, WBRKeyword::NAD+, WBRKeyword::fructose, WBRKeyword::cofactor
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::