Quick revision: every question with its correct answer. For the full explanation, open the relevant test and tap View Solution.
3.1 Bacterial Transposable Elements — Test 1
Q1. The enzyme that catalyses the transposition of an IS (insertion sequence) element is:✓ Transposase
Q2. Which feature is unique to plasmids but NOT true of transposons?✓ They replicate autonomously outside the chromosome
Q3. The simplest bacterial transposable element, carrying only the genes needed for its own movement, is the:✓ Insertion sequence (IS)
Q4. A composite transposon (e.g. Tn5, Tn10) is typically structured as:✓ A central region (often carrying antibiotic resistance) flanked by two IS elements
Q5. Terminal inverted repeats (IRs) at the ends of a transposon serve to:✓ Be recognised and acted upon by transposase
Q6. Upon insertion, most transposons generate a short ______ of the host DNA flanking the element:✓ Direct repeat (target-site duplication)
Q7. In REPLICATIVE transposition, the element:✓ Is copied so that one copy stays at the donor and one appears at the target
Q8. In NON-replicative ('cut-and-paste') transposition, the element:✓ Is excised from the donor and inserted at the target without copying
Q9. The cointegrate intermediate of replicative transposition is resolved into two separate replicons by:✓ Resolvase (site-specific recombinase) acting at res sites
Q10. Antibiotic-resistance genes are commonly spread among bacteria because they are often carried on:✓ Transposons and plasmids (mobile elements)
Q11. An IS element inserted within a bacterial gene typically causes:✓ Inactivation of the gene (insertional mutation)
Q12. Transposon mutagenesis is a useful genetic tool because the transposon:✓ Inserts and disrupts genes, providing a selectable tag at the mutation site
Q13. The target-site duplication flanking a transposon arises from:✓ Staggered (offset) cleavage of the target followed by gap filling
Q14. Which best distinguishes a transposon from a temperate bacteriophage?✓ Transposons have no extracellular (virion) phase
Q15. Tn3 belongs to which transposition class?✓ Replicative (via cointegrate)
Q16. The frequency of transposition is usually kept low because:✓ Transposase is unstable/expressed at low levels and tightly regulated
Q17. Insertion sequences were first recognised in bacteria as the cause of:✓ Strong polar mutations in the gal and lac operons
Q18. Which component is essential at BOTH ends of a functional transposon?✓ Inverted repeat sequences recognised by transposase
Q19. A transposon that carries genes unrelated to transposition (e.g. drug resistance) in addition to transposition genes is called a(n):✓ Complex/composite transposon
Q20. Why can two IS elements flanking any DNA segment mobilise that segment?✓ Transposase can act on the outer inverted repeats, moving everything between them