AP-Micro Microbiology: Microbial Genetics 2 — Questions and Answers
Question 1: Which type of RNA serves as the template for reverse transcriptase in retroviruses?
- mRNA (Correct answer)
- tRNA
- rRNA
- snRNA
Correct answer: mRNA
Retroviruses carry single-stranded mRNA genomes that reverse transcriptase uses as a template to synthesize complementary DNA.
Question 2: In bacterial conjugation, the F factor can integrate into the host chromosome, forming what type of cell?
- F' cell
- Hfr cell (Correct answer)
- R cell
- Prototrophic cell
Correct answer: Hfr cell
When the F factor integrates into the bacterial chromosome, it creates an Hfr (high-frequency recombination) cell capable of transferring chromosomal genes at elevated rates.
Question 3: A frameshift mutation is most likely caused by which of the following?
- A single nucleotide substitution
- Insertion of two nucleotides (Correct answer)
- A nonsense mutation
- UV-induced thymine dimer formation
Correct answer: Insertion of two nucleotides
Frameshift mutations result from insertions or deletions that are not multiples of three, shifting the reading frame; insertion of two nucleotides disrupts the triplet codons downstream.
Question 4: Which enzyme is responsible for removing RNA primers during DNA replication in bacteria?
- DNA polymerase III
- DNA polymerase I (Correct answer)
- Primase
- Ligase
Correct answer: DNA polymerase I
DNA polymerase I removes RNA primers using its 5'→3' exonuclease activity and fills in the resulting gaps with DNA.
Question 5: In Lederberg and Tatum's experiment demonstrating bacterial recombination, auxotrophic strains were used. What is an auxotroph?
- An organism that can synthesize all required nutrients
- An organism that requires an external supply of a specific nutrient (Correct answer)
- A bacterium capable of conjugation
- A bacterium resistant to all antibiotics
Correct answer: An organism that requires an external supply of a specific nutrient
An auxotroph has lost the ability to synthesize a specific nutrient and must obtain it from the environment to grow.
Question 6: The SOS response in bacteria is triggered by which of the following?
- High temperatures
- Accumulation of single-stranded DNA from replication blocks (Correct answer)
- Nutrient deprivation
- Oxygen depletion
Correct answer: Accumulation of single-stranded DNA from replication blocks
Extensive DNA damage causes stalled replication forks and accumulation of single-stranded DNA, which activates RecA protein and induces the SOS repair response.
Question 7: Which of the following best describes a missense mutation?
- A codon changes to a stop codon
- A codon changes to specify a different amino acid (Correct answer)
- One or more bases are deleted
- A codon becomes silent
Correct answer: A codon changes to specify a different amino acid
A missense mutation causes a codon to specify a different amino acid, potentially altering protein function.
AP-Micro Microbiology: Microbial Genetics 2
Which type of RNA serves as the template for reverse transcriptase in retroviruses?