WBR0323
| Author | [[PageAuthor::Rim Halaby, M.D. [1]]] |
|---|---|
| Exam Type | ExamType::USMLE Step 1 |
| Main Category | MainCategory::Genetics |
| Sub Category | SubCategory::General Principles |
| Prompt | [[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 consequently to 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?]] |
| Answer A | AnswerA::Methylation |
| Answer A Explanation | AnswerAExp::Methylation does not make the chromatin transcriptionally active. On the contrary, 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::Acetylation of histones makes the chromatin transcriptionally active. |
| 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::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.
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. |
| Approved | Approved::No |
| Keyword | WBRKeyword::acetylation, WBRKeyword::histone, WBRKeyword::histones, WBRKeyword::chromatin, WBRKeyword::transcription, WBRKeyword::transcriptionally, WBRKeyword::active, WBRKeyword::molecular, WBRKeyword::change, WBRKeyword::changes |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |