Quick revision: every question with its correct answer. For the full explanation, open the relevant test and tap View Solution.
3.3 Eukaryotic Mobile Elements ā Test 1
Q1. Retrotransposons move through the genome by:ā An RNA intermediate that is reverse-transcribed and inserted (copy-and-paste)
Q2. LINEs (Long Interspersed Nuclear Elements) are:ā Autonomous retrotransposons encoding their own reverse transcriptase and endonuclease
Q3. SINEs (Short Interspersed Nuclear Elements), such as Alu, are:ā Non-autonomous; they borrow the retrotransposition machinery of LINEs
Q4. The Alu element is the most abundant SINE in the human genome and is derived from:ā 7SL RNA (signal recognition particle RNA)
Q5. LTR retrotransposons resemble retroviruses but typically:ā Lack a functional env gene, so they cannot form infectious particles
Q6. Yeast Ty elements transpose by:ā An RNA intermediate and reverse transcription (retrotransposition)
Q7. The enzyme essential for retrotransposition that distinguishes it from DNA transposition is:ā Reverse transcriptase
Q8. Barbara McClintock discovered transposable elements ('controlling elements') in:ā Maize (Ac/Ds system)
Q9. In the maize Ac/Ds system, the Ds element is:ā Non-autonomous, requiring Ac to provide transposase
Q10. Retroviruses integrate their genome into host DNA as a:ā Provirus (via reverse transcription and integrase)
Q11. A processed pseudogene is generated when:ā An mRNA is reverse-transcribed and reinserted into the genome (lacking introns/promoter)
Q12. Approximately what fraction of the human genome is composed of transposable-element-derived sequences?ā Nearly half (~45%)
Q13. Full-length human L1 (LINE-1) encodes ORF1 and ORF2; ORF2 provides:ā Endonuclease and reverse transcriptase activities
Q14. Target-primed reverse transcription (TPRT) used by LINEs means that:ā The endonuclease nicks the target, and the freed 3'-OH primes reverse transcription of the element RNA
Q15. Which statement correctly contrasts DNA transposons with retrotransposons?ā DNA transposons use a DNA intermediate (cut/paste or replicative); retrotransposons use an RNA intermediate
Q16. Transposable elements can affect the host genome by all of the following EXCEPT:ā Directly translating host proteins
Q17. Host cells often silence transposable elements through:ā DNA methylation and small-RNA (e.g. piRNA) pathways
Q18. Which is an example of an autonomous eukaryotic retrotransposon?ā LINE-1 (L1)
Q19. The long terminal repeats (LTRs) of LTR retrotransposons and retroviruses function in:ā Transcription initiation/termination and integration of the element
Q20. 5-methylcytosine in DNA is frequently mutated to thymine because it:ā Deaminates to thymine, and CāT at methylated CpG is poorly repaired