WBR0323
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| 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. |
| Approved | Approved::Yes |
| Keyword | WBRKeyword::acetylation, WBRKeyword::histone, WBRKeyword::histones, WBRKeyword::chromatin, WBRKeyword::transcription, WBRKeyword::molecular, WBRKeyword::epigenetics |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |