Bacterial Genetics (Plasmids, Transduction, Transformation, Conjugation)

1. What is a plasmid? A. A bacterial chromosome
B. A eukaryotic organelle
C. A small, circular, extra-chromosomal DNA molecule
D. A viral genome

Explanation: Plasmids are small, circular DNA molecules independent of the bacterial chromosome, often carrying genes for antibiotic resistance.

2. Which of the following processes involves uptake of naked DNA from the environment? A. Conjugation
B. Transduction
C. Transformation
D. Translation

Explanation: Transformation is the process by which bacteria take up naked DNA fragments from their surroundings.

3. What is the role of the F plasmid in conjugation? A. Codes for antibiotic resistance only
B. Enables the synthesis of a sex pilus for DNA transfer
C. Prevents conjugation
D. Integrates into eukaryotic DNA

Explanation: The F (fertility) plasmid contains genes required for the formation of the sex pilus, facilitating DNA transfer during conjugation.

4. What mediates genetic exchange in transduction? A. Plasmids
B. Bacteriophages
C. Sex pili
D. Ribosomes

Explanation: In transduction, bacteriophages (viruses that infect bacteria) transfer DNA from one bacterium to another.

5. Which of the following is true about Hfr strains? A. They have the F plasmid integrated into their chromosome
B. They contain only plasmids
C. They are resistant to phage infection
D. They cannot conjugate

Explanation: Hfr (High frequency recombination) strains result from integration of the F plasmid into the bacterial chromosome, allowing transfer of chromosomal genes during conjugation.

6. Which type of transduction transfers only bacterial genes and no phage genes? A. Specialized transduction
B. Generalized transduction
C. Abortive transduction
D. Lysogeny

Explanation: Generalized transduction occurs when a phage mistakenly packages only bacterial DNA into its capsid.

7. What type of plasmid confers resistance to antibiotics? A. Virulence plasmid
B. R plasmid
C. F plasmid
D. Col plasmid

Explanation: R (resistance) plasmids carry genes that provide resistance to antibiotics and other toxins.

8. What is required for a bacterium to become competent for transformation? A. It must have an F plasmid
B. It must have viral DNA
C. It must express specific surface proteins
D. It must contain a prophage

Explanation: Competent bacteria express specific proteins that allow uptake of extracellular DNA during transformation.

9. Which structure is directly involved in bacterial conjugation? A. Flagella
B. Capsule
C. Sex pilus
D. Endospore

Explanation: The sex pilus forms a connection between donor and recipient cells during conjugation, enabling DNA transfer.

10. What is a transposon? A. A type of plasmid
B. A chromosomal gene
C. A mobile genetic element that can change position
D. A bacteriophage

Explanation: Transposons are mobile DNA elements that can move within or between genomes, contributing to genetic variation and antibiotic resistance.

11. Which enzyme is commonly used by transposons to move? A. DNA polymerase
B. Ligase
C. Transposase
D. Helicase

Explanation: Transposase is the enzyme responsible for cutting and inserting transposons into DNA.

12. What distinguishes specialized transduction from generalized transduction? A. Random DNA is transferred
B. Only genes near the prophage site are transferred
C. No DNA is transferred
D. RNA is transferred

Explanation: In specialized transduction, a lysogenic phage excises incorrectly and takes adjacent bacterial genes with it.

13. What role do insertion sequences play in genetic recombination? A. Encode proteins
B. Prevent recombination
C. Facilitate recombination by providing homology regions
D. Form ribosomes

Explanation: Insertion sequences contain transposase and inverted repeats that help integrate DNA into other genomes.

14. What defines an episome? A. A DNA virus
B. A ribosomal unit
C. A plasmid that can integrate into the host genome
D. A lysogenic phage

Explanation: Episomes are plasmids that can exist independently or integrate into the host chromosome.

15. Which condition promotes transformation in laboratory settings? A. Cold shock followed by heat shock
B. Calcium chloride treatment and heat shock
C. RNA addition
D. UV radiation

Explanation: Calcium chloride increases membrane permeability, and heat shock drives DNA uptake in transformation experiments.

16. Which is a key feature of the lytic cycle in transduction? A. Integration into host genome
B. Host cell lysis and DNA packaging
C. Stable lysogeny
D. Lack of phage proteins

Explanation: In the lytic cycle, the phage replicates and lyses the host, sometimes incorporating host DNA into new phages.

17. What is the function of conjugative plasmids? A. Restrict gene transfer
B. Mediate DNA transfer through conjugation
C. Only replicate DNA
D. Integrate viral genes

Explanation: Conjugative plasmids contain genes (e.g., tra operon) that facilitate the transfer of DNA through conjugation.

18. What does the term "competence" refer to in bacterial transformation? A. Cell division capability
B. Ability to take up extracellular DNA
C. Antibiotic resistance
D. Mutation repair

Explanation: Competent bacteria can internalize extracellular DNA for genetic recombination.

19. Which type of genetic transfer involves direct contact between cells? A. Transformation
B. Transduction
C. Conjugation
D. Transposition

Explanation: Conjugation requires physical contact, often via a sex pilus, to transfer DNA between cells.

20. What is the function of the OriT site in a plasmid? A. Termination of replication
B. Origin of transfer during conjugation
C. Site for antibiotic binding
D. Protein synthesis

Explanation: OriT (origin of transfer) is the site where DNA transfer begins during bacterial conjugation.

21. Which of the following is transferred during bacterial conjugation? A. RNA
B. Proteins
C. Single-stranded DNA
D. Double-stranded RNA

Explanation: A single-stranded copy of the plasmid DNA is transferred to the recipient during conjugation.

22. What happens after DNA from transformation is taken into the cell? A. It is immediately degraded
B. It may integrate into the genome by homologous recombination
C. It becomes a protein
D. It forms RNA

Explanation: Internalized DNA can integrate with the host chromosome through homologous recombination.

23. Which genetic process may be used to map bacterial genes? A. PCR
B. Immunoblotting
C. Interrupted mating in conjugation
D. UV spectroscopy

Explanation: Interrupted mating allows researchers to determine gene order based on transfer timing in Hfr conjugation.

24. What limits host range in phage-mediated transduction? A. Size of bacterial DNA
B. Plasmid type
C. Phage receptor specificity
D. Mutation frequency

Explanation: Phages recognize specific surface molecules, so receptor compatibility limits host range.

25. Which DNA transfer method does not require a living donor? A. Conjugation
B. Transduction
C. Transformation
D. Recombination

Explanation: Transformation can occur with free, naked DNA from dead cells; it doesn’t require a live donor.

26. How are F’ plasmids formed? A. By deletion
B. By incorrect excision of F plasmid from the chromosome
C. By insertion sequences only
D. By phage activity

Explanation: F’ plasmids arise when the F plasmid excises incorrectly, taking some chromosomal genes with it.

27. What is the role of RecA protein in bacteria? A. Transcription
B. Facilitating homologous recombination
C. Protein synthesis
D. Cell division

Explanation: RecA helps align homologous DNA regions and promotes strand exchange during recombination.

28. What kind of DNA can a bacterium acquire through horizontal gene transfer? A. Only viral DNA
B. Its own genome
C. DNA from other bacteria, viruses, or the environment
D. Only RNA

Explanation: Horizontal gene transfer includes acquisition of foreign DNA through transformation, transduction, and conjugation.

29. What structure ensures unidirectional transfer during conjugation? A. DNA helicase
B. Capsule
C. Conjugation bridge
D. Flagella

Explanation: The conjugation bridge formed by the pilus ensures that DNA flows from donor to recipient only.

30. What is meant by lysogenic conversion? A. Bacteria converting into phages
B. Acquisition of new traits due to prophage genes
C. Cell death
D. Sporulation

Explanation: Lysogenic conversion happens when prophage genes provide new properties to the host, like toxin production.