WBR0319: Difference between revisions

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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Rim}}
|QuestionAuthor={{YD}} (Reviewed by Serge Korjian)
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Biochemistry
|MainCategory=Biochemistry
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|MainCategory=Biochemistry
|MainCategory=Biochemistry
|SubCategory=General Principles
|SubCategory=General Principles
|MainCategory=Biochemistry
|MainCategory=Biochemistry
|MainCategory=Biochemistry
|MainCategory=Biochemistry
|MainCategory=Biochemistry
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|MainCategory=Biochemistry
|MainCategory=Biochemistry
|SubCategory=General Principles
|SubCategory=General Principles
|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?  
|Prompt=During DNA synthesis, the nucleoside bears a triphosphate which is employed as a source of energy for the formation of the phosphodiester bond by DNA ligase. Using the simplified diagram below showing only 1 phosphate, at which site does the nucleoside incorporate the triphosphate?  


[[Image:WBR0319.png|400px]]
[[Image:WBR0319.png|400px]]
|Explanation=[[Image:DNASynth.png|400px]]
|Explanation=[[Image:DNASynth.png|400px]]


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.  
In DNA synthesis, the nucleoside bears a 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. The 5' end is termed the "donor" as the energy derived from this reaction is essential for the activity of DNA ligase.
 
|EducationalObjectives= Triphosphate is added at the 5' region of the nucleoside.
 
|AnswerA=A
|AnswerA=A
|AnswerAExp="A" corresponds to the 5' region of the nucleoside. It bears the triphosphate ring.
|AnswerAExp="A" corresponds to the 5' region of the nucleoside. It bears the triphosphate ring.
|AnswerB=B
|AnswerB=B
|AnswerBExp="B" corresponds to the 4' region of the nucleoside. It does not bear the triphosphate ring.
|AnswerBExp="B" corresponds to the 4' region of the nucleoside. It does not bear the triphosphate ring.
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|AnswerCExp="C" corresponds to the 3' region of the nucleoside. It bears the hydoxyl group, where the new nucleotide (containing the triphosphate) is added.
|AnswerCExp="C" corresponds to the 3' region of the nucleoside. It bears the hydoxyl group, where the new nucleotide (containing the triphosphate) is added.
|AnswerD=D
|AnswerD=D
|AnswerDExp="D" corresponds to the hydroxyl group. It does not bear the triphosphate  
|AnswerDExp="D" corresponds to the hydroxyl group. It does not bear the triphosphate
|AnswerE=E
|AnswerE=E
|AnswerEExp="E" corresponds to the 2' region of the nucleoside. It does not bear the triphosphate ring.
|AnswerEExp="E" corresponds to the 2' region of the nucleoside. It does not bear the triphosphate ring.
|EducationalObjectives=Triphosphate is added at the 5' region of the nucleoside.
|References=Kornberg A, Baker TA. DNA Replication. University Science Books; 2005.
|RightAnswer=A
|RightAnswer=A
|WBRKeyword=DNA, synthesis, phosphate, triphosphate, ring, nucleoside, nucleotide, sugar, ring, nitrogenous, base
|WBRKeyword=DNA synthesis, Triphosphate, Nucleoside, Nucleotide, Nitrogenous base, DNA, DNA ligase,  
|Approved=No
|Approved=Yes
}}
}}

Revision as of 20:08, 2 September 2014
Author [[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Serge Korjian)]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Biochemistry
Sub Category SubCategory::General Principles
Prompt [[Prompt::During DNA synthesis, the nucleoside bears a triphosphate which is employed as a source of energy for the formation of the phosphodiester bond by DNA ligase. Using the simplified diagram below showing only 1 phosphate, at which site does the nucleoside incorporate 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 nucleoside bears a 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. The 5' end is termed the "donor" as the energy derived from this reaction is essential for the activity of DNA ligase.
Educational Objective: Triphosphate is added at the 5' region of the nucleoside.
References: Kornberg A, Baker TA. DNA Replication. University Science Books; 2005.]]

Approved Approved::Yes
Keyword WBRKeyword::DNA synthesis, WBRKeyword::Triphosphate, WBRKeyword::Nucleoside, WBRKeyword::Nucleotide, WBRKeyword::Nitrogenous base, WBRKeyword::DNA, WBRKeyword::DNA ligase
Linked Question Linked::
Order in Linked Questions LinkedOrder::
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