ESTUDYR
KAKIRDE EXAM 3 RECOMBINANT DNA MOST
TESTED QUESTIONS AND ANSWERS GRADED A+
WITH RATIONALES
1. Who discovered transposons and how was the discovery made?
A. Kary Mullis — by PCR amplification
B. James Watson — by X-ray crystallography
C. Barbara McClintock — by observing variegated (varied pigment) kernels of Indian corn
D. Frederick Sanger — by sequencing corn DNA
Rationale: McClintock deduced "jumping genes" from mosaic pigment patterns in maize
kernels.
2. Transposons can move between which genetic elements?
A. Only from chromosome to chromosome
B. Between chromosomal DNA, plasmids, and even phage DNA
C. Only between plasmids
D. Only into RNA molecules
Rationale: Transposons are mobile and can insert into chromosomes, plasmids, and phage
genomes.
3. What primary effect do transposons typically have when they insert into a gene?
A. They always restore gene function
B. They methylate the promoter to silence expression
C. They often interrupt the gene and change the phenotype
D. They convert DNA into RNA
Rationale: Insertion disrupts coding sequence or regulation, often altering phenotype.
4. Are transposons considered point mutations?
A. Yes — they are simple point mutations
B. Yes — they only change single bases
C. No — they are mobile genetic elements, not single-base point mutations
D. No — they are types of tRNA
Rationale: Transposons are larger mobile elements; mutations are distinct events.
5. Transposons are typically:
A. Single-stranded DNA elements
B. Double-stranded DNA elements
C. Single-stranded RNA elements only
D. Protein complexes without nucleic acids
Rationale: Most classical transposons are dsDNA.
6. Typical size range for many bacterial transposons is:
A. 10–100 bp
B. 100–500 bp
C. ~1,000–10,000 base pairs (1–10 kb)
D. >1,000,000 bp
Rationale: Bacterial transposons commonly fall in the kb range.
7. Which of the following is NOT one of the three common recombinant DNA tools listed?
A. PCR
B. Plasmids
C. Ribosomes
, ESTUDYR
D. Transposons
Rationale: Ribosomes are cellular machines, not listed recombinant tools; PCR, plasmids,
transposons are common tools.
8. What sequence motifs typically mark the ends of many transposons?
A. Poly-A tails
B. Inverted repeats (short sequences at both ends)
C. Long terminal repeats only found in retroviruses
D. Start and stop codons
Rationale: Inverted repeats flank many DNA transposons and are recognized by transposase.
9. Which enzyme orchestrates transposon excision and insertion?
A. DNA ligase
B. RNA polymerase
C. Transposase
D. Reverse transcriptase
Rationale: Transposase recognizes terminal repeats and mediates cut/paste or copy/paste.
10. What are the two basic types of DNA transposition mechanisms?
A. Transversion and transition
B. Cut & paste (simple transposition) and copy & paste (replicative transposition)
C. Conservative and nonconservative recombination only
D. Horizontal and vertical transposition
Rationale: Some transposons excise (cut/paste); others replicate and insert copies (replicative).
11. When transposase cuts DNA during insertion, what type of ends are commonly created?
A. Blunt ends only
B. Sticky (cohesive) ends that can anneal to complementary sequences
C. RNA overhangs
D. Triphosphate ends
Rationale: Many transposases create staggered cuts producing short single-stranded overhangs
(sticky ends).
12. Which features are commonly found within a bacterial transposon? (choose best single answer)
A. Ribosomal RNA genes only
B. Origins of replication only
C. Terminal inverted repeats, transposase gene, and often antibiotic resistance gene
D. Telomeric repeats
Rationale: Typical composite transposons include IRs, transposase, and cargo such as resistance
genes.
13. Are plasmids essential for bacterial survival under all conditions?
A. Yes — no bacterium exists without plasmids
B. Yes — plasmids carry vital housekeeping genes
C. No — plasmids are usually nonessential but confer advantages under certain conditions
D. No — plasmids are always harmful
Rationale: Plasmids often carry accessory genes (e.g., resistance) beneficial in specific
environments.
14. How do transposons typically select insertion sites?
A. They insert randomly with no sequence preference
B. Many have specific target sequence preferences and produce direct repeats upon insertion
C. They insert only at promoters of rRNA genes
D. They require telomeric sequences
KAKIRDE EXAM 3 RECOMBINANT DNA MOST
TESTED QUESTIONS AND ANSWERS GRADED A+
WITH RATIONALES
1. Who discovered transposons and how was the discovery made?
A. Kary Mullis — by PCR amplification
B. James Watson — by X-ray crystallography
C. Barbara McClintock — by observing variegated (varied pigment) kernels of Indian corn
D. Frederick Sanger — by sequencing corn DNA
Rationale: McClintock deduced "jumping genes" from mosaic pigment patterns in maize
kernels.
2. Transposons can move between which genetic elements?
A. Only from chromosome to chromosome
B. Between chromosomal DNA, plasmids, and even phage DNA
C. Only between plasmids
D. Only into RNA molecules
Rationale: Transposons are mobile and can insert into chromosomes, plasmids, and phage
genomes.
3. What primary effect do transposons typically have when they insert into a gene?
A. They always restore gene function
B. They methylate the promoter to silence expression
C. They often interrupt the gene and change the phenotype
D. They convert DNA into RNA
Rationale: Insertion disrupts coding sequence or regulation, often altering phenotype.
4. Are transposons considered point mutations?
A. Yes — they are simple point mutations
B. Yes — they only change single bases
C. No — they are mobile genetic elements, not single-base point mutations
D. No — they are types of tRNA
Rationale: Transposons are larger mobile elements; mutations are distinct events.
5. Transposons are typically:
A. Single-stranded DNA elements
B. Double-stranded DNA elements
C. Single-stranded RNA elements only
D. Protein complexes without nucleic acids
Rationale: Most classical transposons are dsDNA.
6. Typical size range for many bacterial transposons is:
A. 10–100 bp
B. 100–500 bp
C. ~1,000–10,000 base pairs (1–10 kb)
D. >1,000,000 bp
Rationale: Bacterial transposons commonly fall in the kb range.
7. Which of the following is NOT one of the three common recombinant DNA tools listed?
A. PCR
B. Plasmids
C. Ribosomes
, ESTUDYR
D. Transposons
Rationale: Ribosomes are cellular machines, not listed recombinant tools; PCR, plasmids,
transposons are common tools.
8. What sequence motifs typically mark the ends of many transposons?
A. Poly-A tails
B. Inverted repeats (short sequences at both ends)
C. Long terminal repeats only found in retroviruses
D. Start and stop codons
Rationale: Inverted repeats flank many DNA transposons and are recognized by transposase.
9. Which enzyme orchestrates transposon excision and insertion?
A. DNA ligase
B. RNA polymerase
C. Transposase
D. Reverse transcriptase
Rationale: Transposase recognizes terminal repeats and mediates cut/paste or copy/paste.
10. What are the two basic types of DNA transposition mechanisms?
A. Transversion and transition
B. Cut & paste (simple transposition) and copy & paste (replicative transposition)
C. Conservative and nonconservative recombination only
D. Horizontal and vertical transposition
Rationale: Some transposons excise (cut/paste); others replicate and insert copies (replicative).
11. When transposase cuts DNA during insertion, what type of ends are commonly created?
A. Blunt ends only
B. Sticky (cohesive) ends that can anneal to complementary sequences
C. RNA overhangs
D. Triphosphate ends
Rationale: Many transposases create staggered cuts producing short single-stranded overhangs
(sticky ends).
12. Which features are commonly found within a bacterial transposon? (choose best single answer)
A. Ribosomal RNA genes only
B. Origins of replication only
C. Terminal inverted repeats, transposase gene, and often antibiotic resistance gene
D. Telomeric repeats
Rationale: Typical composite transposons include IRs, transposase, and cargo such as resistance
genes.
13. Are plasmids essential for bacterial survival under all conditions?
A. Yes — no bacterium exists without plasmids
B. Yes — plasmids carry vital housekeeping genes
C. No — plasmids are usually nonessential but confer advantages under certain conditions
D. No — plasmids are always harmful
Rationale: Plasmids often carry accessory genes (e.g., resistance) beneficial in specific
environments.
14. How do transposons typically select insertion sites?
A. They insert randomly with no sequence preference
B. Many have specific target sequence preferences and produce direct repeats upon insertion
C. They insert only at promoters of rRNA genes
D. They require telomeric sequences
