WBR0979
Author | [[PageAuthor::Rim Halaby, M.D. [1]]] |
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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.
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. |
Approved | Approved::No |
Keyword | WBRKeyword::NADPH, WBRKeyword::NAD+, WBRKeyword::fructose, WBRKeyword::cofactor |
Linked Question | Linked:: |
Order in Linked Questions | LinkedOrder:: |