WBR0319

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Biochemistry
Sub Category	SubCategory::General Principles
Prompt	[[Prompt::During DNA synthesis, the nucleotide containing the nitrogenous base bears a triphosphate, which will be the source of energy for the DNA synthesis process. Using the simplified diagram below showing only 1 phosphate, at which site does the nucleoside bear the triphosphate? ]]
Answer A	AnswerA::A
Answer A Explanation	AnswerAExp::"A" corresponds to the 5' region of the nucleoside. It bears the triphosphate ring.
Answer B	AnswerB::B
Answer B Explanation	AnswerBExp::"B" corresponds to the 4' region of the nucleoside. It does not bear the triphosphate ring.
Answer C	AnswerC::C
Answer C Explanation	AnswerCExp::"C" corresponds to the 3' region of the nucleoside. It bears the hydoxyl group, where the new nucleotide (containing the triphosphate) is added.
Answer D	AnswerD::D
Answer D Explanation	AnswerDExp::"D" corresponds to the hydroxyl group. It does not bear the triphosphate
Answer E	AnswerE::E
Answer E Explanation	AnswerEExp::"E" corresponds to the 2' region of the nucleoside. It does not bear the triphosphate ring.
Right Answer	RightAnswer::A
Explanation	[[Explanation:: In DNA synthesis, the sugar and the nitrogenous base bear the triphosphate at the 5' region of the sugar. When the nucleotide (nucleoside + triphosphate) is added to the pre-existing chain at the 3' region of the sugar, 2 phosphates are released and one phosphate remains in the chain. Educational Objective: Triphosphate is added at the 5' region of the nucleoside. References: ]]
Approved	Approved::No
Keyword	WBRKeyword::DNA, WBRKeyword::synthesis, WBRKeyword::phosphate, WBRKeyword::triphosphate, WBRKeyword::ring, WBRKeyword::nucleoside, WBRKeyword::nucleotide, WBRKeyword::sugar, WBRKeyword::ring, WBRKeyword::nitrogenous, WBRKeyword::base
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::