14 Bacterial Genetics - MicroCore Review Center

Which of the following is the main polymerizing enzyme in DNA replication?

• RNA polymerase

• DNA polymerase

• DNA ligase

• Primase

Answer explanation

Answer: B. In bacteria, three main types of DNA polymerases are known: DNA pol I, DNA pol II, and DNA pol III. It is now known that DNA pol III is the enzyme required for DNA synthesis; DNA pol I and DNA pol II are primarily required for repair.

 

Reference: Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A. (2018). Brock Biology of Microorganisms. 15^th ed. Pearson Higher Education.

What is the enzyme that is used to seal breaks in the phosphate backbone of DNA?

• Restriction endonuclease

• DNA polymerase

• Reverse transcriptase

• DNA ligase

Answer explanation

Answer: D. DNA ligases join breaks in the phosphodiester backbone of DNA molecules and are used in many essential reactions within the cell. All DNA ligases follow the same reaction mechanism, but they may use either ATP or NAD+ as a cofactor.

 

Reference: Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A. (2018). Brock Biology of Microorganisms. 15^th ed. Pearson Higher Education.

Which of the following refers to an adenine to guanine substitution?

• Transition mutation

• Transversion mutation

• Deletion

• Insertion

Answer explanation

Answer: A. Transition mutations occur when a pyrimidine base (i.e., thymine [T] or cytosine [C]) substitutes for another pyrimidine base or when a purine base (i.e., adenine [A] or guanine [G]) substitutes for another purine base.

 

Reference: Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A. (2018). Brock Biology of Microorganisms. 15^th ed. Pearson Higher Education.

Palero, F., & Crandall, K. (2009). Phylogenetic inference using molecular data. In Crustacean issues (pp. 67–88). https://doi.org/10.1201/9781420092592-c5

Which of the following results in a +1 frameshift mutation?

• Deletion

• Silent mutation

• Insertion

• Missense mutation

Answer explanation

Answer: C. A frameshift mutation in a gene refers to the insertion or deletion of nucleotide bases in numbers that are not multiples of three. An insertion results in +1frameshift mutation.

 

Reference: Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A. (2018). Brock Biology of Microorganisms. 15^th ed. Pearson Higher Education.

Which of the following events results in spontaneous mutation?

• Action of mobile genetic elements

• Error in DNA replication

• Head-on collisions of replisome

• All of the aforementioned choices

Answer explanation

Answer: D. Spontaneous mutations are those mutations that occur in the absence of exogenous chemical or physical agents. Spontaneous mutations occur at a rate of 1 in 10^5 to 10^8 and contribute to random population variation. Since bacteria are haploid for the majority of their genes and have short generation turnover, phenotypic variation due to point mutations can occur relatively quickly.

 

Reference: Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A. (2018). Brock Biology of Microorganisms. 15^th ed. Pearson Higher Education.

Which base substitution mutation results in a truncated protein?

• Silent

• Nonsense

• Missense

• Neutral

Answer explanation

Answer: B. A nonsense mutation occurs in DNA when a sequence change gives rise to a stop codon rather than a codon specifying an amino acid. The presence of the new stop codon results in the production of a shortened protein that is likely non-functional. 

 

Reference: Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A. (2018). Brock Biology of Microorganisms. 15^th ed. Pearson Higher Education.

Intercalating agents cause mutations by

• Modifying bases in situ

• Adding alkyl residues to bases

• Inserting between base pairs

• Replacing normal bases

Answer explanation

Answer: C. Intercalating agents are polyaromatic compounds that can insert themselves between two adjacent base pairs in the DNA double strands and inhibit the synthesis of nucleic acid in vivo. Examples are ethidium bromide, acridine orange, and actinomycin D.

 

Reference: Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A. (2018). Brock Biology of Microorganisms. 15^th ed. Pearson Higher Education.

Transformation is a type of horizontal gene transfer mechanism wherein an exogenous DNA enters a competent cell

• TRUE

• FALSE

Answer explanation

Answer: TRUE. Mechanisms of bacterial horizontal gene transfer include transformation, transduction, and conjugation. During transformation, a DNA fragment from a dead, degraded bacterium enters a competent recipient bacterium and is exchanged for a piece of DNA of the recipient.

 

Reference: Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A. (2018). Brock Biology of Microorganisms. 15^th ed. Pearson Higher Education.

The RNA polymerase of eukaryotes are more structurally similar to bacteria than in archaea.

• TRUE

• FALSE

Answer explanation

Answer: FALSE. In bacteria, all transcription is performed by a single type of RNA polymerase. This polymerase contains four catalytic subunits and a single regulatory subunit known as sigma. In eukaryotes, transcription is achieved by three different types of RNA polymerase (RNA pol I-III). These polymerases differ in the number and type of subunits they contain, as well as the class of RNAs they transcribe; that is, RNA pol I transcribes ribosomal RNAs (rRNAs), RNA pol II transcribes RNAs that will become messenger RNAs (mRNAs) and also small regulatory RNAs, and RNA pol III transcribes small RNAs such as transfer RNAs (tRNAs).

Archaeal RNA Polymerase is complex than bacterial one and it is more similar than Eukaryotic RNA Polymerases. Archaea contain only a single RNA polymerase that most closely resembles eukaryotic RNA polymerase II. Both Archaea and Eukarya have RNA polymerase which have 11 or 12 subunits. But Bacterial RNA Polymerase have only 5 subunits (including sigma factor)

 

Reference: Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A. (2018). Brock Biology of Microorganisms. 15^th ed. Pearson Higher Education.

http://rnaplab.org/research/#

Prokaryotes can start translation before transcription is complete.

• TRUE

• FALSE

Answer explanation

 

Answer: TRUE. Prokaryotic translation is the process of translating the information on the messenger RNA into a series of amino acids that make up the protein. Translation in prokaryotes begins before transcription is completed. Proteins can start to be assembled immediately because more than one gene is coded on the mRNA.

 

Reference: Madigan, M. T., Bender, K. S., Buckley, D. H., Sattley, W. M., & Stahl, D. A. (2018). Brock Biology of Microorganisms. 15^th ed. Pearson Higher Education.