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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Rim}}
|QuestionAuthor= {{SSK}} {{Alison}} (Reviewed by Serge Korjian)
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Genetics
|MainCategory=Genetics
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|MainCategory=Genetics
|MainCategory=Genetics
|SubCategory=General Principles
|SubCategory=General Principles
|MainCategory=Genetics
|MainCategory=Genetics
|MainCategory=Genetics
|MainCategory=Genetics
|MainCategory=Genetics
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|MainCategory=Genetics
|MainCategory=Genetics
|SubCategory=General Principles
|SubCategory=General Principles
|Prompt=A researcher is studying the regulation of transcription in mice. In his experiment, he shows that core histones undergo specific molecular changes at unique lysine residues to neutralize their positively charged tail and to consequently decrease their affinity for DNA. These changes enable regulatory proteins to access chromatin templates required for transcription. Which molecular change most likely occurs to histones in the researcher's observations?
|Prompt=A researcher, studying the regulation of transcription in mice, shows that core histones undergo molecular changes at particular lysine residues, in order to neutralize their positively charged tail and to decrease their affinity for DNA. These changes enable regulatory proteins to access chromatin templates, which are required for transcription. Which of the following molecular changes is most likely to impact the histones in the researcher's observations?
|Explanation=Core histone acetylation is important for transcription of eukaryotic cells. When core histones (H2A, H2B, H3, H4) are acetylated, they associate with transcriptionally active chromatin. Acetylation of histones occurs at specific lysine residues at the tails of histones. This process will neutralize the positively charged histone and will decrease its affinity for DNA. Consequently, the nucleosomal confirmation is altered and the accessibility of transcription factors is facilitated at the level of chromatin templates.
|Explanation=Acetylation of core histones, such as H2A, H2B, H3, and H4, plays a major role in the regulation of transcription in eukaryotic cells. The acetylation of lysine residues at the tails of histones neutralizes its positively charge and decreases its affinity for DNA. Consequently, the alteration of nucleosomal conformation facilitates the transcription at the level of chromatin templates.
 
Educational Objective:
Histone acetylation is important for increasing transcriptional activity.
 
Reference:
Struhl K. Histone acetylation and transcriptional regulatory mechanisms. Genes Dev. 1998;12:599-606.
 
|AnswerA=Methylation
|AnswerA=Methylation
|AnswerAExp=Methylation does not make the chromatin transcriptionally active. On the contrary, methylation "mutes" chromatin.
|AnswerAExp=Methylation hinders transcription at the level of chromatin templates. Methylation "mutes" chromatin.
|AnswerB=Phosphorylation
|AnswerB=Phosphorylation
|AnswerBExp=Phosphorylation does not make the chromatin transcriptionally active.
|AnswerBExp=Phosphorylation does not make the chromatin transcriptionally active.
|AnswerC=Acetylation
|AnswerC=Acetylation
|AnswerCExp=Acetylation of histones makes the chromatin transcriptionally active.
|AnswerCExp=See explanation.
|AnswerD=Oxidation
|AnswerD=Oxidation
|AnswerDExp=Oxidation does not make the chromatin transcriptionally active.
|AnswerDExp=Oxidation does not make the chromatin transcriptionally active.
|AnswerE=Dehydrogenation
|AnswerE=Dehydrogenation
|AnswerEExp=Dehydrogenation does not make the chromatin transcriptionally active.
|AnswerEExp=Dehydrogenation does not make the chromatin transcriptionally active.
|EducationalObjectives=Histone acetylation is crucial in the regulation of eukaryotic transcriptional activity.
|References=Struhl K. Histone acetylation and transcriptional regulatory mechanisms. Genes Dev. 1998;12:599-606.
|RightAnswer=C
|RightAnswer=C
|WBRKeyword=acetylation, histone, histones, chromatin, transcription, transcriptionally, active, molecular, change, changes
|WBRKeyword=acetylation, histone, histones, chromatin, transcription, molecular, epigenetics
|Approved=No
|Approved=Yes
}}
}}

Latest revision as of 00:11, 28 October 2020
Author [[PageAuthor::Serge Korjian M.D. (Reviewed by Alison Leibowitz) (Reviewed by Serge Korjian)]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Genetics
Sub Category SubCategory::General Principles
Prompt [[Prompt::A researcher, studying the regulation of transcription in mice, shows that core histones undergo molecular changes at particular lysine residues, in order to neutralize their positively charged tail and to decrease their affinity for DNA. These changes enable regulatory proteins to access chromatin templates, which are required for transcription. Which of the following molecular changes is most likely to impact the histones in the researcher's observations?]]
Answer A AnswerA::Methylation
Answer A Explanation AnswerAExp::Methylation hinders transcription at the level of chromatin templates. Methylation "mutes" chromatin.
Answer B AnswerB::Phosphorylation
Answer B Explanation AnswerBExp::Phosphorylation does not make the chromatin transcriptionally active.
Answer C AnswerC::Acetylation
Answer C Explanation AnswerCExp::See explanation.
Answer D AnswerD::Oxidation
Answer D Explanation AnswerDExp::Oxidation does not make the chromatin transcriptionally active.
Answer E AnswerE::Dehydrogenation
Answer E Explanation AnswerEExp::Dehydrogenation does not make the chromatin transcriptionally active.
Right Answer RightAnswer::C
Explanation [[Explanation::Acetylation of core histones, such as H2A, H2B, H3, and H4, plays a major role in the regulation of transcription in eukaryotic cells. The acetylation of lysine residues at the tails of histones neutralizes its positively charge and decreases its affinity for DNA. Consequently, the alteration of nucleosomal conformation facilitates the transcription at the level of chromatin templates.

Educational Objective: Histone acetylation is crucial in the regulation of eukaryotic transcriptional activity.
References: Struhl K. Histone acetylation and transcriptional regulatory mechanisms. Genes Dev. 1998;12:599-606.]]

Approved Approved::Yes
Keyword WBRKeyword::acetylation, WBRKeyword::histone, WBRKeyword::histones, WBRKeyword::chromatin, WBRKeyword::transcription, WBRKeyword::molecular, WBRKeyword::epigenetics
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