WBR0973

Author	[[PageAuthor::Rim Halaby, M.D. [1] (Reviewed by Yazan Daaboul, M.D.)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Biochemistry
Sub Category	SubCategory::General Principles
Prompt	[[Prompt::Variations in blood and urine concentrations of a molecule X are analyzed in two groups of rats fed with either high protein or low protein diet. Shown below is the structure of molecule X. In this molecule, carbon dioxide is the donor of the carbon and oxygen moieties, while ammonia is the donor of one amino group moiety. Which of the following amino acids is the donor of the second amino group moiety in molecule X? ]]
Answer A	AnswerA::Aspartate
Answer A Explanation	[[AnswerAExp::Aspartate is the donor of the second amino group of the urea molecule.]]
Answer B	AnswerB::Arginine
Answer B Explanation	[[AnswerBExp::Arginine is not the donor of the second amino group of the urea molecule.]]
Answer C	AnswerC::Lysine
Answer C Explanation	[[AnswerCExp::Lysine is not the donor of the second amino group of the urea molecule.]]
Answer D	AnswerD::Fumarate
Answer D Explanation	[[AnswerDExp::Fumarate is not the donor of the second amino group of the urea molecule.]]
Answer E	AnswerE::Alanine
Answer E Explanation	[[AnswerEExp::Alanine is not the donor of the second amino group of the urea molecule.]]
Right Answer	RightAnswer::A
Explanation	[[Explanation::One molecule of urea (molecule X of this vignette) is composed of two amino groups (-NH2), one carbon atom (C), and one oxygen atom (O). Both the carbon and oxygen atoms are donated from carbon dioxide. One amino group is donated from ammonia, while the other amino group is donated from the amino acid aspartate. Educational Objective: The urea molecule is composed of 2 amino groups, 1 carbon atom, and 1 oxygen atom. One amino group is donated from ammonia, while the other amino group is donated from the amino acid aspartate. References: First Aid 2014 page 108]]
Approved	Approved::Yes
Keyword	WBRKeyword::Urea, WBRKeyword::Amino group, WBRKeyword::Aspartate, WBRKeyword::Carbon dioxide, WBRKeyword::Amino acid, WBRKeyword::Molecule X
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::