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 the biological age of cells due to their cumulative oxidative 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. Educational Objective: References: ]]
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
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