Microbial Genetics Practice Questions

Q: A strain of E. coli shows resistance to multiple antibiotics, including penicillin, tetracycline, and chloramphenicol. This resistance is transferred to a non-resistant strain through direct contact. What is the most likely mechanism of resistance transfer?

Conjugation. ***Conjugation*** - **Conjugation** is the transfer of genetic material, often in the form of **plasmids** carrying antibiotic resistance genes, directly between bacteria through a **pilus**. - The description of resistance being transferred to a non-resistant strain through **direct contact** is characteristic of conjugation. *Transformation* - **Transformation** involves the uptake of **naked DNA** from the environment by a bacterial cell; it does not require direct cell-to-cell contact. - While it can transfer resistance, the "direct contact" aspect of the question specifically points away from transformation as the primary mechanism. *Transduction* - **Transduction** is the transfer of DNA between bacteria via a **bacteriophage (virus)**. - This mechanism involves viral intermediates and not direct contact between bacterial cells for transfer, contradicting the scenario. *Mutation* - A **mutation** is a spontaneous change in the bacterial genome that can lead to antibiotic resistance, but it's an alteration within a single bacterium rather than a mechanism of **transfer** to another strain. - The question specifies the **transfer** of resistance to a non-resistant strain, which mutations alone cannot explain.

Q: Which of the following is not a recognized mechanism of gene transfer in bacteria?

Vertical gene transfer. ***Vertical gene transfer*** - **Vertical gene transfer (VGT)** is the transmission of genetic information from parent to offspring through reproduction, which is a fundamental mode of inheritance but not a mechanism for acquiring new genetic material from other, unrelated bacterial cells. - While VGT ensures the continuity of a species' genetic makeup, it does not introduce novel genes or traits from external sources, which is the hallmark of horizontal gene transfer mechanisms that bacteria use for adaptation and evolution. *Conjugation* - **Conjugation** is a process where genetic material, often in the form of plasmids, is transferred directly from one bacterium to another through a **pilus (sex pilus)**. - This is a significant mechanism of **horizontal gene transfer**, allowing bacteria to acquire new traits like antibiotic resistance and virulence factors. *Transduction* - **Transduction** involves the transfer of bacterial DNA from one bacterium to another via a **bacteriophage (bacterial virus)**. - This mechanism of **horizontal gene transfer** occurs when phages accidentally package host DNA and transfer it to recipient bacteria, contributing to bacterial evolution and pathogenicity. *Transformation* - **Transformation** is the uptake of naked DNA from the environment by competent bacterial cells. - This is the third major mechanism of **horizontal gene transfer**, first discovered in *Streptococcus pneumoniae* by Griffith (1928), and is crucial for bacterial genetic diversity and antibiotic resistance spread.

Q: Natural method of horizontal gene transfer among bacteria that involves direct cell-to-cell contact through a pilus includes:

Conjugation. ***Conjugation*** - **Conjugation** involves the direct transfer of genetic material (usually a plasmid or a portion of the bacterial chromosome) from one bacterium to another through cell-to-cell contact, mediated by a **sex pilus**. - This process is a common natural mechanism for the spread of **antibiotic resistance genes** and other virulence factors among bacteria. *Transduction* - **Transduction** is the process where bacterial DNA is transferred from one bacterium to another by a **bacteriophage** (a virus that infects bacteria). - While it is a natural method of horizontal gene transfer, it relies on a viral vector, which is distinct from direct cell-to-cell contact. *Transformation* - **Transformation** is the uptake of **naked extracellular DNA** from the environment by a bacterial cell. - This DNA can originate from lysed bacterial cells and can then be incorporated into the recipient bacterium's genome. *Electroporation* - **Electroporation** is an **artificial laboratory technique** used to introduce foreign DNA into cells (including bacteria) by applying a brief, high-voltage electric pulse. - This pulse creates temporary pores in the cell membrane, allowing DNA to enter, and is not a natural process of horizontal gene transfer.

Q: R-factor in bacteria is transferred by ?

Conjugation. ***Conjugation*** - **R-factors** (resistance plasmids) are commonly transferred between bacteria via **conjugation**, a process involving direct cell-to-cell contact through a **pilus**. - This allows bacteria to share genetic material, including genes for **antibiotic resistance**, which is a significant mechanism for the spread of multi-drug resistance. *Transduction* - **Transduction** involves the transfer of genetic material (including R-factors) by a **bacteriophage** (virus) from one bacterium to another. - While possible, it's a less common or primary mechanism for widespread R-factor dissemination compared to conjugation. *Transformation* - **Transformation** is the uptake of **naked DNA** from the environment by a competent bacterial cell. - While R-factors can exist as free DNA, widespread transfer through this mechanism is less efficient for intact plasmid transfer across diverse bacterial populations. *Vertical transmission* - **Vertical transmission** refers to the inheritance of genetic material, including plasmids, from a **parent bacterial cell to its daughter cells** during cell division. - This is a means of maintaining R-factors within a clonal population, but it does not account for the horizontal transfer of R-factors between different bacterial cells or species.

Q: By which method foreign DNA is introduced into a cell by a virus or viral vector?

Transduction. ***Transduction*** - **Transduction** is the process by which foreign DNA is introduced into a cell by a **virus** or **viral vector**. - This method is widely used in **genetic engineering** and **gene therapy** to deliver genes into target cells. *Transcription* - **Transcription** is the process where a segment of **DNA** is copied into **RNA** by the enzyme **RNA polymerase**. - It describes the synthesis of RNA from a DNA template within a cell and is not a mechanism for introducing foreign DNA. *Transformation* - **Transformation** is the genetic alteration of a cell resulting from the direct uptake, incorporation, and expression of **exogenous genetic material** (DNA) from its surroundings. - While it involves introducing foreign DNA, it typically refers to the uptake of naked DNA by bacteria, not via a viral vector. *Lysogenic conversion* - **Lysogenic conversion** occurs when a temperate **bacteriophage** integrates its DNA into the host bacterium's genome (**lysogeny**), leading to the expression of new genes carried by the phage. - While it involves phage DNA, it's a specific phenomenon associated with bacteriophages altering bacterial phenotypes, not a general method for introducing foreign DNA into diverse cell types using viral vectors.

Q: Viral DNA is integrated into Bacterial DNA in:

Lysogenic cycle. ***Lysogenic cycle*** - In the **lysogenic cycle**, the **bacteriophage DNA integrates** into the host bacterial chromosome, becoming a **prophage**. - This integration allows the viral genome to be **replicated along with the host DNA** without immediately lysing the cell. *Bacterial transduction* - **Transduction** involves the transfer of **bacterial DNA** from one bacterium to another via a bacteriophage, not the integration of viral DNA into the host genome. - While phages are involved, the primary event is the accidental packaging and transfer of bacterial genes, not viral integration into the host for replication. *Bacterial transformation* - **Transformation** is the process where bacteria take up **naked DNA from their environment** and incorporate it into their own genome. - This DNA is typically from another bacterium or is artificially introduced, not viral DNA undergoing a natural integration process within the cell. *Bacterial conjugation* - **Conjugation** is the transfer of genetic material (usually a **plasmid**) between bacteria through direct cell-to-cell contact, mediated by a **pilus**. - This process involves the transfer of bacterial or plasmid DNA, not the integration of a viral genome into the host chromosome.

Q: The gene encoding cholera toxin is carried on -

Bacteriophage. ***Bacteriophage*** - The gene encoding **cholera toxin (ctxA and ctxB)** is carried on the genome of a **lysogenic bacteriophage** known as CTXf. - This phage integrates its DNA into the *Vibrio cholerae* chromosome, allowing for toxin production. *Chromosomal DNA* - While the **phage DNA (containing the cholera toxin gene)** integrates into the *Vibrio cholerae* chromosome, the toxin itself is **not directly encoded by the core bacterial chromosomal DNA** but by the integrated phage DNA. - Many bacterial virulence factors are encoded on the main chromosome, but cholera toxin is a specific exception. *Extrachromosomal plasmid* - **Plasmids** are extrachromosomal DNA molecules that can carry virulence genes, but the cholera toxin gene is **not typically found on a plasmid** in *Vibrio cholerae*. - Examples of plasmid-encoded toxins include some enterotoxins in *E. coli*. *Transposon* - **Transposons** are "jumping genes" that can move within and between DNA molecules, but they are generally **mobile genetic elements** that carry genes, not the direct source of the cholera toxin gene. - While transposons can sometimes contribute to the movement of virulence genes, the cholera toxin gene specifically originates from a bacteriophage.

Q: Which of the following statements is NOT applicable to bacterial genomes?

Its DNA has both introns and exons. ***Its DNA has both introns and exons*** - **Bacterial genomes** are typically organized as continuous coding sequences and **lack introns** (non-coding regions) that are characteristic of eukaryotic genes. - The presence of introns and their subsequent splicing is a hallmark of **eukaryotic gene expression**, not prokaryotic. *It is composed of DNA* - The genetic material of bacteria, like all cellular life forms, is primarily composed of **DNA (deoxyribonucleic acid)**. - DNA serves as the blueprint for all cellular processes and hereditary information. *It does not contain histones* - **Bacterial DNA** is typically compacted by various DNA-binding proteins, but these are not the **histone proteins** found in eukaryotes. - Histones are fundamental for packaging DNA into **chromatin** in eukaryotic cells. *It is circular* - The main chromosome in most bacteria is **covalently closed** and **circular**, unlike the linear chromosomes found in eukaryotes. - This circular structure aids in replication and stability within the bacterial cell.

Q: Bacteria can transfer genetic information through all of the following methods except:

Through meiotic recombination. ***Through meiotic recombination*** - **Meiotic recombination** (crossing over) is a process that occurs during **meiosis**, which is cell division specific to sexually reproducing eukaryotes. - Bacteria reproduce asexually through **binary fission** and do not undergo meiosis, thus meiotic recombination is not a mechanism for genetic transfer in bacteria. *Through conjugation* - **Conjugation** is a direct transfer of genetic material (usually a **plasmid**) from one bacterium to another through a **pilus**. - This process allows for the spread of genes, such as those conferring **antibiotic resistance**. *Through bacteriophages* - Genetic transfer via **bacteriophages** is known as **transduction**. - Bacteriophages are **viruses that infect bacteria**, occasionally transferring bacterial DNA from one host to another during their reproductive cycle. *By taking up soluble DNA fragments across their cell wall from other species* - This process is called **transformation**, where bacteria directly take up **naked DNA fragments** from their environment. - Transformation can occur naturally in some bacterial species or can be induced in laboratory settings, allowing for the acquisition of new genetic traits.

Question 1

A strain of E. coli shows resistance to multiple antibiotics, including penicillin, tetracycline, and chloramphenicol. This resistance is transferred to a non-resistant strain through direct contact. What is the most likely mechanism of resistance transfer?

Accepted Answer

Conjugation

Answer

Transformation

Answer

Transduction

Answer

Mutation

Question 2

Which of the following is not a recognized mechanism of gene transfer in bacteria?

Accepted Answer

Vertical gene transfer

Answer

Transformation

Answer

Conjugation

Answer

Transduction

Question 3

Natural method of horizontal gene transfer among bacteria that involves direct cell-to-cell contact through a pilus includes:

Accepted Answer

Conjugation

Answer

Transduction

Answer

Transformation

Answer

Electroporation

Question 4

R-factor in bacteria is transferred by ?

Accepted Answer

Conjugation

Answer

Transduction

Answer

Transformation

Answer

Vertical transmission

Question 5

By which method foreign DNA is introduced into a cell by a virus or viral vector?

Accepted Answer

Transduction

Answer

Transcription

Answer

Transformation

Answer

Lysogenic conversion

Question 6

Viral DNA is integrated into Bacterial DNA in:

Accepted Answer

Lysogenic cycle

Answer

Bacterial transduction

Answer

Bacterial transformation

Answer

Bacterial conjugation

Question 7

The gene encoding cholera toxin is carried on -

Accepted Answer

Bacteriophage

Answer

Chromosomal DNA

Answer

Extrachromosomal plasmid

Answer

Transposon

Question 8

Which of the following statements is NOT applicable to bacterial genomes?

Accepted Answer

Its DNA has both introns and exons

Answer

It is composed of DNA

Answer

It does not contain histones

Answer

It is circular

Question 9

Bacteria can transfer genetic information through all of the following methods except:

Accepted Answer

Through meiotic recombination

Answer

Through conjugation

Answer

Through bacteriophages

Answer

By taking up soluble DNA fragments across their cell wall from other species

Microbial Genetics — MCQs

Microbial Genetics — MCQs

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