WBR0324
| 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 geneticist is studying the process of aging in rat cells. He reports finding specific G-rich region that undergo single strand breaks following oxidative damage. Based on his experiment, he shows that these regions reflect the replicative potential and cumulative damage sustained by somatic cells. Which regions of DNA are most likely referred to by the geneticist?]] |
| Answer A | AnswerA::Exons |
| Answer A Explanation | AnswerAExp::Exons are coding regions of DNA. |
| Answer B | AnswerB::Introns |
| Answer B Explanation | AnswerBExp::Introns are non-coding regions of DNA. |
| Answer C | AnswerC::Promoters |
| Answer C Explanation | AnswerCExp::Promoters are specific regions of DNA where RNA polymerase and transcription factors bind to DNA. They are located upstream of the transcribed sequence. |
| Answer D | AnswerD::Telomeres |
| Answer D Explanation | AnswerDExp::Telomeres are specific regions on DNA that play a role in the replicative potential of cells and cell senescence. |
| Answer E | AnswerE::Enhancers |
| Answer E Explanation | AnswerEExp::Enhancers are specific regions on DNA that bind to transcription factors and alter gene expression. They are located anywhere along or outside the transcribed DNA region. |
| Right Answer | RightAnswer::D |
| Explanation | [[Explanation::Telomeres are specific regions located at the end of the DNA. The regulation mechanisms of both telomere length and replication are significant for the integrity of the genome. Telomeres are important regions because they have a role in cell senescence and the replicative potential of cells. The length of telomeres is regulated by telomerase and by the replication fork itself. If telomerases are absent, the length of telomeres is shortened with every replication until. Once the length reaches a lower limit, replicative senescence, called Hayflick limit, is induced. Additionally, G-rich overhanging regions at the end of telomeres are susceptible to oxidative damage, whose cumulative effects is associated with the biological age of somatic cells.
Educational Objective: Telomeres are important for the replicative potential of cells and for identifying the biological age of somatic cells. References: Salpea KD, Humphries SE. Telomere length in atherosclerosis and diabetes. Atherosclerosis. 2010; 209(1):35-38. Waga S, Stillman B. The DNA replication fork in eukaryotic cells. Annu. Rev. Biochem. 1998; 67:721-51. |
| Approved | Approved::No |
| Keyword | WBRKeyword::telomere, WBRKeyword::length, WBRKeyword::replicative, WBRKeyword::potential, WBRKeyword::replication, WBRKeyword::age, WBRKeyword::cell, WBRKeyword::senescence, WBRKeyword::biological, WBRKeyword::G-rich, WBRKeyword::oxidative, WBRKeyword::damage |
| Linked Question | Linked:: |
| Order in Linked Questions | LinkedOrder:: |