Microbial Genetics — MCQs

Microbial Genetics Indian Medical PG Practice Questions and MCQs

Question 71: What role do plasmids play in bacterial adaptation and survival?

A. They provide structural support to the cell wall
B. They facilitate the synthesis of essential vitamins
C. They can transfer genetic material between bacteria (Correct Answer)
D. They detoxify harmful substances in the environment

Explanation: ***They can transfer genetic material between bacteria*** - Plasmids are **extrachromosomal DNA molecules** that can carry genes for traits like **antibiotic resistance** or virulence factors. - They are readily exchanged between bacteria through processes like **conjugation**, horizontal gene transfer, allowing rapid adaptation to new environments or threats. *They provide structural support to the cell wall* - The primary function of the **bacterial cell wall** is to provide structural support and protection, mainly composed of **peptidoglycan**. - Plasmids are genetic elements and play no role in the structural integrity of the cell wall. *They facilitate the synthesis of essential vitamins* - The synthesis of essential vitamins in bacteria is primarily carried out by **chromosomal genes** encoding metabolic pathways. - While some plasmids can carry metabolic genes, this is not their primary or most significant role in adaptation and survival compared to horizontal gene transfer. *They detoxify harmful substances in the environment* - Detoxification of harmful substances is often managed by chromosomal genes or specific enzyme systems within the bacterium. - While some plasmids can carry genes conferring resistance to heavy metals or other toxins, it's a specific function rather than a general role for all plasmids.

Question 72: 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?

A. Transformation
B. Transduction
C. Conjugation (Correct Answer)
D. Mutation

Explanation: ***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.

Question 73: Which of the following is not a recognized mechanism of gene transfer in bacteria?

A. Vertical gene transfer (Correct Answer)
B. Transformation
C. Conjugation
D. Transduction

Explanation: ***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.

Question 74: Natural method of horizontal gene transfer among bacteria that involves direct cell-to-cell contact through a pilus includes:

A. Conjugation (Correct Answer)
B. Transduction
C. Transformation
D. Electroporation

Explanation: ***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.

Question 75: R-factor in bacteria is transferred by ?

A. Transduction
B. Transformation
C. Conjugation (Correct Answer)
D. Vertical transmission

Explanation: ***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.

Question 76: Which of the following statements is NOT applicable to bacterial genomes?

A. It is composed of DNA
B. It does not contain histones
C. It is circular
D. Its DNA has both introns and exons (Correct Answer)

Explanation: ***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.

Question 77: Bacteria can transfer genetic information through all of the following methods except:

A. Through conjugation
B. Through bacteriophages
C. Through meiotic recombination (Correct Answer)
D. By taking up soluble DNA fragments across their cell wall from other species

Explanation: ***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.

Practice by Chapter

Bacterial Genome Organization

Practice Questions

Plasmids and Mobile Genetic Elements

Practice Questions

Bacterial Gene Expression

Practice Questions

Mutation and Mutagenesis

Practice Questions

Gene Transfer in Bacteria

Practice Questions

Transposons and Insertion Sequences

Practice Questions

Bacterial Genetic Recombination

Practice Questions

Regulation of Gene Expression

Practice Questions

CRISPR-Cas Systems

Practice Questions

Bacterial Stress Responses

Practice Questions

Genetics of Antimicrobial Resistance

Practice Questions

Genetic Basis of Bacterial Virulence

Practice Questions

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