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 fructose 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. Fructose is converted to fructose 1 phosphate under the action of fructokinase which requires NADPH as a cofactor. Fructose 1 phosphate is converted to dihydroxyacetone phosphate and glyceraldehyde under the action of aldolase B which requires NAD+. Shown below is a diagram depicting the metabolism of fructose.
Educational objective: Fructose is converted to fructose 1 phosphate under the action of fructokinase which requires NADPH as a cofactor. Fructose 1 phosphate is converted to dihydroxyacetone phosphate and glyceraldehyde under the action of aldolase B 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:: |
