WBR0973
| Author | [[PageAuthor::Rim Halaby, M.D. [1]]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Biochemistry |
| Sub Category | SubCategory::General Principles |
| Prompt | [[Prompt::Variation of blood and urine levels of a molecule X is analyzed in two groups of rats fed with either high protein or low protein diet. Shown below is the structure of the molecule X.
In this molecule, carbon dioxide is the donor of the carbon and ammonia is the donor of one of the nitrogen. Which of the following amino acids is the source of the second nitrogen in this molecule?]] |
| Answer A | AnswerA::Aspartate |
| Answer A Explanation | [[AnswerAExp::Aspartate is the donor of the second nitrogen atom of the urea molecule.]] |
| Answer B | AnswerB::Arginine |
| Answer B Explanation | [[AnswerBExp::Arginine is not the donor of the second nitrogen atom of the urea molecule.]] |
| Answer C | AnswerC::Lysine |
| Answer C Explanation | [[AnswerCExp::Lysine is not the donor of the second nitrogen atom of the urea molecule.]] |
| Answer D | AnswerD::Fumarate |
| Answer D Explanation | [[AnswerDExp::Fumarate is not the donor of the second nitrogen atom of the urea molecule.]] |
| Answer E | AnswerE::Alanine |
| Answer E Explanation | [[AnswerEExp::Alanine is not the donor of the second nitrogen atom of the urea molecule.]] |
| Right Answer | RightAnswer::A |
| Explanation | [[Explanation::The molecule depicted in the question is urea. Urea is formed by two nitrogen, one carbon and one oxygen atoms. The carbon and oxygen atoms are derived from carbon dioxide. The nitrogen atoms are derived from ammonia and the amino acid aspartate.
Educational objective: The nitrogen atoms are derives from ammonia and the amino acid aspartate. Reference:
First Aid for the USMLE step 1. Page 106. |
| Approved | Approved::No |
| Keyword | WBRKeyword::urea, WBRKeyword::aspartate |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |
