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::Sorbitol levels were measured in the lenses of normal rats and mutant rats with glucose intolerance. The aim of the experiment is to detect any association between the level of glucose in the blood and the level of sorbitol in the lenses. 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 sorbitol 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::