MicroBiology MCQs with Answer and Explnation | Chapter 35

Answer: It can be cultured from RBCs of infected persons

Cytomegalovirus (CMV) predominantly targets white blood cells and epithelial cells, not red blood cells (RBCs). While CMV DNA can be detected in peripheral blood mononuclear cells (PBMCs) of infected individuals, viral culture from RBCs is unsuccessful due to the lack of necessary cellular machinery for CMV replication.

The other options are incorrect:

• It can be transmitted transplacentally: This is true. CMV can cross the placenta and infect fetuses during pregnancy, potentially leading to congenital CMV infection.
• It can be activated by immunosuppressive agents: This is also true. Immunosuppressive medications and conditions can weaken the immune system, allowing latent CMV infections to reactivate and cause disease.
• It can cause retinitis: This is true. CMV retinitis is a serious complication of CMV infection, particularly in individuals with compromised immunity, causing inflammation and vision loss in the retina.

Answer: Produce cytopathic effects in many conventional cell culture systems

While some rotavirus strains can replicate in specific cell lines (e.g., MA104 cells), they generally do not produce pronounced cytopathic effects (CPEs) in standard cell culture systems. This makes traditional virus isolation challenging and necessitates indirect detection methods like ELISA or antigen detection for diagnosis.

The other options are incorrect:

• Produce an infection that is seasonally distributed peaking in fall and winter: This is true. Rotavirus infections often exhibit seasonality, with higher incidence in colder months due to increased indoor crowding and contact.
• Can be sensitively and rapidly detected in stools by the ELISA technique: This is true. Enzyme-linked immunosorbent assay (ELISA) is a sensitive and specific method for detecting rotavirus antigens in stool samples, facilitating rapid diagnosis.
• Have been implicated as a major etiologic agent of infantile gastroenteritis: This is true. Rotavirus is the leading cause of severe diarrheal illness in young children worldwide, accounting for a significant portion of hospitalizations and deaths.

Answer: Expression vector

An expression vector is a type of vector specifically designed to facilitate the expression of a gene of interest. In this context, a gene for insulin has been inserted into the vector to produce the protein product (insulin).

The other options are incorrect:

• Suppression vector: This term is not appropriate in the context of expressing a gene for insulin. Suppression vectors are typically associated with the downregulation or suppression of gene expression.
• Storage vector for genomic library: Genomic libraries are typically constructed using storage vectors, but these vectors are not designed for the expression of proteins. They are used for the storage and maintenance of genomic DNA fragments for future analysis.

Answer: Tc or cytotoxic T-cells

MHC-I molecules present intracellular antigens on the surface of infected cells. Cytotoxic T-cells (Tc cells) are specifically designed to recognize and destroy these infected cells based on the antigen-MHC complex. They achieve this by releasing cytotoxic molecules that kill the infected cell, eliminating the intracellular pathogen.

The other options are incorrect:

• Neutrophils: While neutrophils play a crucial role in fighting bacterial infections and inflammation, they don’t directly target intracellular antigens like Tc cells.
• TH cells: These are helper T cells that provide crucial signals to activate other immune cells, including Tc cells, but they don’t directly kill infected cells themselves.
• CD68 cells: These are macrophages primarily involved in phagocytosis and antigen presentation, not directly killing infected cells like Tc cells.

Answer: Thymus

The primary site for the development, maturation, and differentiation of T lymphocytes is the thymus. This specialized organ provides the necessary environment for T cells to undergo selection processes, ensuring they recognize foreign antigens while avoiding reactivity against self-tissue.

The other options are incorrect:

• Bursa of Fabricius: This organ in birds is important for B lymphocyte development, not T cells.
• Liver: The liver plays a key role in hematopoiesis (blood cell production), but it’s not directly involved in T cell development.
• Tonsils: Tonsils are secondary lymphoid organs that mainly function as surveillance posts for the immune system, not primary sites for T cell development.

Answer: Bursa of Fabricious

Birnaviruses, specifically Infectious Bursal Disease Virus (IBDV), primarily target and destroy the Bursa of Fabricius in chickens. The Bursa of Fabricius is a lymphoid organ involved in the development and maturation of B cells, and its destruction by IBDV can lead to immunosuppression in affected birds.

The other options are incorrect:

• Heart: Birnaviruses do not typically target the heart in chickens. The Bursa of Fabricius is the primary organ affected.
• Lungs: Birnaviruses do not have a specific tropism for the lungs in chickens. The main target is the Bursa of Fabricius.
• Thymus: The thymus is not the primary organ affected by birnaviruses in chickens. The Bursa of Fabricius is the main target due to its role in the development and maturation of B cells.

Answer: Clostridium tetani

Clostridium tetani is an example of an obligate anaerobic bacterium. Obligate anaerobes are microorganisms that can only survive and grow in environments devoid of oxygen. Clostridium tetani is the causative agent of tetanus and thrives in anaerobic conditions.

The other options are incorrect:

• Bacillus anthracis: Bacillus anthracis is a facultative anaerobe, meaning it can grow in both aerobic and anaerobic conditions. It is the bacterium responsible for anthrax.
• Brucella abortus: Brucella abortus is a facultative intracellular bacterium, but it is not strictly obligate anaerobic. It can grow in both aerobic and anaerobic environments.
• Salmonella: Salmonella is a facultative anaerobe. It can survive and grow in the presence or absence of oxygen, adapting to different environments.

Answer: IgA

Immunoglobulin A (IgA) is the antibody class mainly involved in mucosal immunity. It is the predominant antibody found in mucosal secretions, such as saliva, tears, and respiratory and gastrointestinal tract secretions. IgA plays a crucial role in preventing pathogens from entering the body through mucosal surfaces.

The other options are incorrect:

• IgY: IgY is found in birds and reptiles but is not the main antibody class involved in mucosal immunity in mammals.
• IgD: IgD is primarily found on the surface of B cells and is involved in the initiation of the immune response. It is not the primary antibody class in mucosal immunity.
• IgE: IgE is involved in allergic responses and is not the main antibody class associated with mucosal immunity. IgA is more relevant in protecting mucosal surfaces.

Answer: Alum

The oldest and traditionally used adjuvant in vaccines is alum (aluminum salts). Alum has been used for many years to enhance the immune response to vaccines by promoting the persistence of antigens at the injection site and stimulating the immune system.

The other options are incorrect:

• BCG: The Bacillus Calmette-Guérin (BCG) vaccine itself is actually a live attenuated form of the tuberculosis bacterium and not an adjuvant. While it can induce non-specific immune responses, it’s not widely used as a general adjuvant for other vaccines.
• ISCOMS: Immunostimulatory complexes (ISCOMS) are relatively newer adjuvants developed in the 1980s. They offer specific advantages for certain vaccines, but their overall use in existing vaccines remains less widespread compared to alum.
• Montanide: This oil-based adjuvant is considered more potent than alum but also carries a higher risk of side effects like local inflammation and granuloma formation. Its use is therefore restricted to specific vaccines where a stronger immune response is needed and can tolerate the potential for increased side effects.

Answer: Recombinant plasmid

A plasmid is a small, circular piece of DNA that exists independently from the chromosomal DNA of a cell. When a foreign DNA segment is inserted into a plasmid, it becomes a recombinant plasmid. This new plasmid combines the original plasmid DNA with the inserted foreign DNA, creating a hybrid molecule.

The other options are incorrect:

• Non-coding DNA: Not all non-coding DNA is “junk.” While some non-coding regions may not directly code for proteins, they can play important roles in regulating gene expression and other cellular processes. A recombinant plasmid can contain both coding and non-coding DNA from both the original plasmid and the inserted fragment.
• Junk DNA: This term is generally used to describe non-coding DNA sequences with no known function. However, the inserted foreign DNA in a recombinant plasmid can have a specific function, such as encoding a protein of interest.

Answer: Plasmids

The extra-chromosomal, self-replicating, double-stranded, closed, circular DNA molecules are called plasmids. Plasmids are commonly found in bacteria and can replicate independently of the bacterial chromosomal DNA. They are often used in genetic engineering and biotechnology.

The other options are incorrect:

• Phages: Bacteriophages (phages) are viruses that infect bacteria. They are not self-replicating, circular DNA molecules; instead, they inject their genetic material into the host bacterium.
• Viruses: Viruses are genetic entities that can have DNA or RNA as their genetic material. Unlike plasmids, viruses are not always double-stranded, circular DNA molecules, and they require a host cell for replication.
• Chloroplasts: Chloroplasts are organelles found in plant cells, responsible for photosynthesis. They contain their own DNA but are not extra-chromosomal, self-replicating molecules. Chloroplast DNA is usually in the form of multiple copies of a circular genome within the organelle.

Answer: Transposons

Transposons are the aptly named “jumping genes” in bacterial DNA. They are mobile genetic elements that can cut themselves out of one location in the genome and insert themselves into another, potentially impacting gene expression and function. This mobility earned them the nickname “jumping genes.”

The other options are incorrect:

• Volutin: This is a type of storage granule found in some bacteria and archaea, not a mobile genetic element.
• Endosomes: These are membrane-bound organelles involved in internalization and processing of extracellular materials, not DNA elements.
• Histones: These are protein molecules that package and organize DNA in eukaryotic chromosomes, not mobile genetic elements found in bacteria.

Answer: Sub-unit vaccine

TTS, or Tetanus Toxoid Vaccine, is a sub-unit vaccine used to provide immunity against tetanus. It contains a detoxified form of the tetanus toxin (toxoid), which stimulates the immune system to produce an immune response without causing the disease.

The other options are incorrect:

• DNA vaccine: DNA vaccines involve the introduction of genetic material (usually plasmid DNA) encoding antigens into the host. TTS is not a DNA vaccine; it is based on a protein sub-unit.
• Attenuated vaccine: Attenuated vaccines use weakened forms of live microorganisms to induce an immune response. TTS is not an attenuated vaccine; it does not contain live bacteria.
• Autogenous vaccine: Autogenous vaccines are custom-made vaccines produced from the specific pathogens isolated from a patient. TTS is not an autogenous vaccine; it is a standardized vaccine used to prevent tetanus in the general population.

Answer: Chimeric gene

A chimeric gene is formed by combining DNA from two different sources, resulting in a hybrid gene with novel characteristics. In your example, it involves joining a gene from one organism with the regulatory sequence of another. This combination can alter the expression and function of the original gene, potentially leading to new features or functionalities.

The other options are incorrect:

• Oncogene: An oncogene is a gene that has the potential to cause cancer. It is not necessarily a gene produced for rDNA technology but rather a term associated with cancer-causing genes.
• Junk gene: “Junk gene” is not a scientifically recognized term. The concept of “junk DNA” refers to non-coding regions of DNA with no known function, but it is not directly related to the creation of chimeric genes.
• Oncogene (repeated): Oncogene was already mentioned. It is not the correct term for a gene produced for rDNA technology with genetic material from different organisms.

Answer: IgD

IgD (Immunoglobulin D) is not typically present in chicken. IgY is the predominant antibody class in birds, serving functions similar to IgG in mammals.

The other options are incorrect:

• IgY: IgY is present in chicken and is the avian counterpart to mammalian IgG. It plays a role in avian immune responses.
• IgG: IgG is present in chicken, as well as in mammals. It is an important antibody class involved in immune responses, including secondary immune responses.
• IgM: IgM is present in chicken and other vertebrates. It is an early responder antibody class produced during the primary immune response.

Answer: Two DNA segments

A recombinant DNA molecule is produced by joining together two DNA segments. Recombinant DNA technology involves combining genetic material from different sources, typically by inserting a specific DNA segment into another DNA molecule, such as a plasmid or a vector.

The other options are incorrect:

• One mRNA with a DNA segment: Joining an mRNA molecule with a DNA segment is technically possible but not a standard practice in creating recombinant DNA. Moreover, mRNA is inherently unstable and less suitable for manipulation compared to DNA.
• One mRNA with a tRNA segment: Similar to the previous option, combining mRNA and tRNA is not a typical approach in recombinant DNA technology. Both molecules have specific roles in translation, not in forming hybrid DNA molecules.
• Two mRNA molecules: While mRNA molecules can interact through splicing mechanisms, they cannot directly join together to form a stable recombinant DNA molecule. The double-stranded structure and inherent stability of DNA make it the preferred substrate for recombination.

Answer: Population

A group of genetically similar organisms obtained by sexual reproduction is called a population. In a population, individuals share common characteristics due to the exchange of genetic material through sexual reproduction.

The other options are incorrect:

• Clone: A clone refers to genetically identical individuals derived from a single parent through asexual reproduction. Sexual reproduction is not involved in the creation of clones.
• Assembly: “Assembly” is not a term used in this context. The correct term for a group of genetically similar organisms through sexual reproduction is a population.

Answer: Blue/violet

After Gram’s staining, Gram-positive bacteria retain the blue/violet stain. This staining technique helps differentiate bacteria based on the characteristics of their cell walls. Gram-positive bacteria have a thicker peptidoglycan layer in their cell walls, which retains the crystal violet dye used in the staining process.

The other options are incorrect:

• Green: Gram-positive bacteria do not appear green after Gram’s staining. Green is not a characteristic color associated with Gram staining.
• Yellow: Yellow is not the color typically associated with Gram-positive bacteria after Gram’s staining. The characteristic color is blue/violet.
• Red: Gram-negative bacteria, not Gram-positive bacteria, typically appear red after Gram’s staining. The red color is due to the counterstain used in the process

Answer: Candida albicans

Candida albicans is an example of yeast. Yeasts are a type of fungus that belongs to the division Ascomycota. Candida albicans is commonly found as a part of the normal flora in the human gastrointestinal tract and mucous membranes, but it can also cause infections under certain conditions.

The other options are incorrect:

• Mucor: Mucor is an example of a mold, not a yeast. It belongs to the phylum Zygomycota.
• Rhizopus: Rhizopus is also an example of a mold, not a yeast. It belongs to the phylum Zygomycota.
• Penicillium: Penicillium is a genus of molds, not yeasts. It is known for producing the antibiotic penicillin. Yeasts and molds are different forms of fungi, with yeasts typically existing as single-celled organisms.

Answer: Mycobacterium

Mycolic acid is a characteristic component of the cell wall of Mycobacterium species, which include the bacteria responsible for diseases such as tuberculosis (Mycobacterium tuberculosis) and leprosy (Mycobacterium leprae). Mycolic acids contribute to the unique structure and resistance of the mycobacterial cell wall.

The other options are incorrect:

• Listeria: These bacteria possess peptidoglycan in their cell wall, but not mycolic acids.
• Mycoplasma: Unique bacteria that lack an entire cell wall, thus completely missing mycolic acids.
• Staphylococcus: These bacteria have a cell wall composed of peptidoglycan and teichoic acids, again lacking mycolic acids.

Answer: An origin of replication

To be useful in the preparation of recombinant DNA, a plasmid must have an origin of replication. The origin of replication is a specific DNA sequence where the process of DNA replication initiates, allowing the plasmid to replicate independently within a host cell.

The other options are incorrect:

• No origin of replication: Without this specific sequence, the plasmid wouldn’t replicate and be lost, rendering it useless for recombinant DNA preparation.
• The ability to alternate between the linear and circular forms: While some plasmids can exist in both forms, this property isn’t necessary for their use in recombinant DNA technology.
• Restriction endonuclease activity: These enzymes cut DNA at specific sites, often used for manipulating the plasmid and inserting the gene of interest. However, the plasmid itself doesn’t need to possess this activity.

Answer: Insulin

The first human protein successfully produced through recombinant DNA technology was insulin. This groundbreaking achievement in 1978 significantly improved diabetes treatment by providing a readily available, bioidentical form of the hormone.

The other options are incorrect:

• Erythropoietin: This protein was also produced early using recombinant DNA technology, but slightly later than insulin. It stimulates red blood cell production and is used in treating anemia.
• Interferon: A group of naturally occurring proteins with antiviral and immunomodulatory properties. While recombinant interferons were developed later, they weren’t the first human protein obtained through this technology.
• Somatostatin: This hormone regulates various physiological functions, including growth and metabolism. Its recombinant production followed insulin and other proteins in the timeline of recombinant DNA technology advancements.

Answer: Eli Lilly and Company

While Genentech developed Humulin through groundbreaking recombinant DNA technology, Eli Lilly and Company licensed it and became the first company to bring it to market in 1982. This marked a significant milestone in diabetes treatment, offering patients a bioidentical and readily available form of insulin.

The other options are incorrect:

• Biocon India Limited: This Indian pharmaceutical company is a leader in biosimilars but wasn’t involved in the initial development or marketing of Humulin.
• Glaxo: Although a major pharmaceutical company, Glaxo (now GlaxoSmithKline) wasn’t involved in producing or marketing Humulin.
• Cipla: Another Indian pharmaceutical company known for its affordable versions of essential medicines, Cipla wasn’t involved in the original Humulin development and marketing.

Answer: β-galactosidase gene

In one of the techniques of recombinant insulin production, the genes for α and β polypeptides were inserted into the plasmid by the side of the β-galactosidase gene. This approach allows the use of the lac operon promoter and operator system to regulate the expression of the inserted genes.

The other options are incorrect:

• Ori: While the origin of replication is crucial for plasmid maintenance, it wouldn’t directly affect insulin gene expression and isn’t typically used as an insertion site.
• Antibiotic resistant gene: Antibiotic resistance markers are commonly used on plasmids but are typically located separate from the gene of interest to avoid product contamination.
• Restriction endonuclease gene: These enzymes are used to cut the plasmid and insert the insulin genes but aren’t permanently included in the final recombinant plasmid

Answer:

Endonucleases are enzymes that cleave within a polynucleotide chain, meaning they break internal phosphodiester bonds within the DNA molecule. They do not cut DNA at the ends, which is the characteristic of exonucleases.

The other options are incorrect:

• Externally: Incorrect. As explained above, endonucleases cleave internal bonds, not those at the ends.
• Both ‘Externally’ and ‘B’: Invalid. Option B is “Internally,” so this becomes a nonsensical choice.
• Neither ‘Externally’ nor ‘Internally’: Incorrect. Endonucleases are specifically defined by their ability to cleave DNA internally.

Answer: 2 Polypeptide chains

Insulin is a protein hormone consisting of two polypeptide chains. These chains are referred to as the A chain and B chain. The A chain contains 21 amino acids, and the B chain contains 30 amino acids. The two chains are connected by disulfide bonds, forming the functional structure of insulin.

The other options are incorrect:

• 3 Polypeptide chains: Although some proteins consist of three or more chains, insulin is an exception with only two.
• 4 Polypeptide chains: Similar to the reasoning above, four chains are too many for insulin.
• More than 4 Polypeptide chains: Insulin is a relatively simple protein and definitely doesn’t contain more than four chains.

Answer: Cows and pigs

Before the development of recombinant DNA technology in the late 1970s, insulin for treating human diabetes was extracted from the pancreas glands of cows and pigs. This method remained the primary source of insulin until recombinant insulin became commercially available.

The other options are incorrect:

• Healthy humans: Extracting insulin from healthy humans wouldn’t be ethical or practical as it would require significant amounts of pancreatic tissue, potentially harming the donor.
• Dead human body: While potentially possible, obtaining enough pancreatic tissue from deceased individuals wouldn’t be a reliable and sustainable source for widespread insulin production.
• Dogs and cats: Although technically possible, these animals were not commonly used for insulin extraction due to lower insulin yield and potential immunological differences compared to pigs and cows.

Answer: Insulin

Genetic engineering involves manipulating an organism’s genetic makeup to produce desired traits or products. In 1982, Humulin, a genetically engineered version of human insulin, became the first drug approved for use in the United States and other countries. This was a major breakthrough in the treatment of diabetes, as it provided a readily available and consistent source of insulin for patients.

The other options are incorrect:

• Interferon: While interferons were among the first proteins produced through genetic engineering, the first licensed drug was Humulin.
• Penicillin: Penicillin is an antibiotic derived from a mold, not through genetic engineering.
• Somatotropin: Growth hormone, also known as somatotropin, was genetically engineered later than Humulin and wasn’t the first licensed drug.

Answer: pUC 18

The plasmid generally used for the production of recombinant insulin is pUC 18. Plasmids are circular DNA molecules often used as vectors in genetic engineering. pUC 18 is a common plasmid vector that contains features useful for the cloning and expression of genes, making it suitable for the production of recombinant proteins like insulin.

The other options are incorrect:

• RK 646: RK 646 is not a well-known plasmid vector used in genetic engineering for the production of recombinant proteins.
• Ti plasmid: The Ti plasmid is commonly used for transferring genes into plants, particularly in the creation of genetically modified plants. It is not typically used for producing recombinant insulin.
• ACY 17: ACY 17 is not a widely recognized plasmid vector used for the production of recombinant insulin. The commonly used vectors for insulin production are often derivatives of pUC vectors.

Answer: In vitro culture

To save Rauwolfia serpentina from the threat of extinction, in vitro culture techniques can be useful. In vitro culture involves growing cells, tissues, or organs outside their natural environment, providing a controlled environment for propagation. This technique helps in conserving plant species facing endangerment.

The other options are incorrect:

• Genetic engineering: Genetic engineering involves manipulating the genetic material of an organism. While it can be applied to enhance certain traits, it may not be the most suitable technique for saving a species from extinction.
• DNA fingerprinting: DNA fingerprinting is a technique used to identify and analyze the genetic characteristics of an organism. It is not typically employed for the conservation of endangered plant species.
• Hybridoma technology: Hybridoma technology is used in the production of monoclonal antibodies. It is not a primary technique for the conservation of plant species under threat of extinction.

Answer: Ligases

Ligases are popularly called “Molecular stitchers.” They are enzymes that play a crucial role in the process of DNA replication and repair by joining or sealing breaks in the phosphodiester backbone of DNA strands. Ligases are often referred to as “Molecular stichers” because of their function in linking or ligating DNA fragments.

The other options are incorrect:

• Restriction Endonuclease: Restriction endonucleases are enzymes that cut DNA at specific recognition sites. They are not referred to as “Molecular stichers.”
• RNA polymerase: RNA polymerase is an enzyme responsible for synthesizing RNA from a DNA template during transcription. It is not known as a “Molecular stitcher.”
• DNA polymerase: DNA polymerase is an enzyme involved in synthesizing DNA strands during DNA replication. While it plays a crucial role in DNA synthesis, it is not typically referred to as a “Molecular stitcher.”

Answer: DNA at specific sites

Restriction endonucleases have the ability to cut DNA at specific sites. These enzymes recognize and cleave DNA at specific nucleotide sequences, known as recognition sites or restriction sites. The cuts are usually precise and occur within or near the recognition sequence.

The other options are incorrect:

• DNA at random sites: While some rare types of restriction endonucleases exist with less well-defined recognition, the vast majority and the ones commonly used in the lab cut DNA at specific sequences.
• Both ‘DNA at random sites’ and ‘DNA at specific sites’: As explained above, this is not accurate. The defining characteristic of these enzymes is their specificity in cutting DNA.
• DNA and RNA at random sites: Restriction endonucleases only target double-stranded DNA, they do not cut RNA (which is single-stranded) and they do not cut at random sites in DNA.

Answer: Asexual method and genetically similar

Cloning refers to the process of producing individuals with identical genetic makeup. This process usually involves asexual reproduction, where a single organism or its parts give rise to offspring without the involvement of genetic material from another individual. Therefore, clones share the same genetic code as the parent organism.

The other options are incorrect:

• Asexual method and genetically dissimilar: While variations can occur through mutations, asexual reproduction typically results in offspring genetically identical to the parent.
• Sexual method and genetically similar: Sexual reproduction involves combining genetic material from two parents, leading to genetic variations in offspring.
• Sexual method and genetically dissimilar: This statement is redundant as the previous point already explains that sexual reproduction leads to genetic diversity.

Answer: Produce protein products

Expression vectors are specialized DNA molecules designed to introduce a gene of interest into a host cell and trigger its expression. This means the host cell’s machinery will read the introduced gene and translate it into a functional protein. Therefore, the primary function of expression vectors is protein production.

The other options are incorrect:

• Used for genomic libraries: Genomic libraries are large collections of DNA fragments representing an organism’s entire genome. While expression vectors can contain DNA fragments, they are not specifically used for constructing or storing whole genomes.
• Used for chromosome synthesis: Chromosomes are complex structures containing an organism’s genetic material. Though expression vectors can carry DNA, they are not directly involved in synthesizing or manipulating entire chromosomes.
• Used for fingerprinting: DNA fingerprinting is a technique for identifying individuals based on their unique genetic patterns. While expression vectors can contain DNA, they are not used in the analysis or identification of individuals through DNA fingerprinting.

Answer: All of these

E. coli is generally used for gene cloning because it possesses several advantageous characteristics.

• It supports the replication of recombinant DNA: E. coli is capable of replicating foreign DNA, making it suitable for maintaining and propagating recombinant DNA molecules.
• It is easy to transform: E. coli is easily transformed, meaning that it can take up foreign DNA, such as plasmids containing cloned genes.
• It is free from elements that interfere with replication and recombination of DNA: E. coli has a relatively simple genome, and it lacks certain elements that might interfere with the replication and recombination of foreign DNA.

Answer: One recognition site for one restriction endonuclease

An ideal plasmid to be used for recombinant DNA technology should have only one recognition site for one restriction endonuclease. This ensures that the insertion of foreign DNA into the plasmid occurs at a specific, controlled location, facilitating the cloning process.

The other options are incorrect:

• Minimum amount of DNA: The size of the plasmid is not a critical factor for its use in recombinant DNA technology. The key consideration is the presence of specific features, such as a single recognition site for a restriction endonuclease.
• Relaxed replication control: Plasmids with relaxed replication control may replicate more abundantly, but it is not a crucial criterion for an ideal plasmid used in recombinant DNA technology.
• All of these: While the aspects mentioned in the options may have some importance, having “all of these” is not a requirement for an ideal plasmid. The critical factor is the specificity of recognition sites for restriction endonucleases.

Answer: Restriction site

Restriction endonucleases are enzymes that recognize and cut double-stranded DNA molecules at specific and short sequences called restriction sites. These sites are typically palindromic, meaning they read the same forwards and backwards. The precise cutting ability of restriction enzymes makes them vital tools in various molecular biology techniques like gene cloning, genetic engineering, and DNA analysis.

The other options are incorrect:

• Ligation site: Ligation sites are specific sequences where DNA molecules can be joined together by an enzyme called DNA ligase. While restriction enzymes and ligases play crucial roles in recombinant DNA technology, they target different sites for their respective functions.
• ori: The origin of replication (ori) is a specific sequence on DNA where replication initiates. Although restriction enzymes might be active near the ori in some bacterial genomes, their primary target is not the ori itself, but rather specific short sequences throughout the DNA molecule.
• Replication site: Replication sites are broad regions on DNA where replication machinery binds and copies the DNA. Restriction enzymes, on the other hand, target and cleave specific short sequences within the DNA molecule, not entire replication regions.

Answer: Heat treatment

Transferring a recombinant plasmid into E. coli typically involves a process called heat shock. This technique briefly exposes the bacterial cells to a high temperature (usually around 42°C for a few seconds) followed by a rapid chilling step. This sudden temperature change temporarily makes the bacterial membrane more permeable, allowing the plasmid DNA to enter the cell.

The other options are incorrect:

• UV-rays treatment: While UV-rays can damage DNA, they are not commonly used for plasmid transfer into E. coli. In fact, high UV exposure can even kill the bacteria.
• MgCl2 treatment: Magnesium chloride (MgCl2) is sometimes used in transformation buffers to enhance the efficiency of the process, but it is not the main factor responsible for plasmid uptake.
• Lysis: Lysis refers to the breakdown of a cell membrane. While disrupting the cell membrane can allow DNA entry, it would also kill the bacteria, preventing them from taking up and expressing the plasmid.

Answer: Cyanogen bromide

During recombinant insulin synthesis, the bond between the insulin polypeptide and galactosidase can be removed by using cyanogen bromide. Cyanogen bromide cleaves the peptide bond at the carboxyl side of methionine residues, and it is commonly used for selective cleavage in peptide and protein chemistry.

The other options are incorrect:

• Chymotrypsin: Chymotrypsin cleaves peptide bonds at the carboxyl side of aromatic amino acids (tyrosine, tryptophan, and phenylalanine), not at methionine residues.
• Carboxy peptidase: Carboxypeptidase cleaves peptide bonds at the carboxyl end of the peptide chain, not at methionine residues.
• Amylase: Amylase is an enzyme that hydrolyzes the bonds in starch, not peptide bonds in proteins. It is not used for the removal of the bond between insulin polypeptide and galactosidase in recombinant insulin synthesis.

Answer: Plasmids, phages can be used as vectors

Plasmids and phages can be used as vectors in genetic engineering. Vectors are DNA molecules used to transfer foreign genetic material into a host organism. Plasmids and phages are commonly employed as vectors in molecular biology and biotechnology.

The other options are incorrect:

• All vectors are plasmids only: This is incorrect. While plasmids are common vectors, other types exist, including phages, viral vectors, and even some types of bacteria and fungi.
• Fungi can also be used as vectors: While some fungi can be used to transfer genetic material to other fungi, they are not as widely used or as well-developed as plasmids or phages as vectors.
• Cyanobacteria can also be used as vectors: Similar to fungi, while some research is exploring using cyanobacteria as vectors, it is not a common or well-established method.

Answer: Plasmids are present in bacteria only

Plasmids are present in bacteria only. Plasmids are small, circular DNA molecules that exist independently of the chromosomal DNA in bacteria. They carry additional genetic information and can replicate independently within bacterial cells.

The other options are incorrect:

• Plasmids are present in all organisms: This is incorrect. While plasmids are common in bacteria and archaea, they are not found in all organisms. Plants, animals, and other eukaryotes primarily rely on their linear chromosomes for genetic information.
• Plasmids present in bacteria and phages: This is also incorrect. Phages are viruses that infect bacteria, and they have their own distinct genetic material (single-stranded or double-stranded DNA or RNA) that is separate from the bacterial chromosome and plasmids.
• Plasmids present in plants and animals: This is again incorrect. As mentioned earlier, plasmids are not found in eukaryotes like plants and animals. Their genetic information is mainly stored in linear chromosomes within the nucleus.

Answer: Plasmid

Plasmids are circular, extrachromosomal DNA molecules that can replicate independently of the host cell’s chromosome. They often carry genes that provide advantages to the organism, like antibiotic resistance or the ability to metabolize specific compounds. This ability to self-replicate and carry additional genetic material defines them as “autonomously replicating minichromosomes.”

The other options are incorrect:

• Virus: Viruses are non-cellular entities that contain their own genetic material (DNA or RNA). They cannot replicate on their own and require a host cell to hijack its machinery for replication. This dependence on a host makes them ineligible for the definition of an autonomously replicating minichromosome.
• Phage: While closely related to viruses, phages are typically larger and more complex. They also rely on host cells for replication, making them unsuitable for the description “autonomously replicating.”
• Lichen: Lichens are not single organisms but symbiotic partnerships between a fungus and algae or cyanobacteria. Their genetic material resides within the individual organisms, not in extrachromosomal elements like plasmids. Therefore, they cannot be considered autonomously replicating minichromosomes.

Answer: They have DNA that is as long as chromosomal DNA

“They have DNA that is as long as chromosomal DNA” is NOT attributed to plasmids. Plasmids are small, circular DNA molecules that are separate from the chromosomal DNA. They typically have a much smaller size compared to the chromosomal DNA.

The other options are incorrect:

• They are circular DNA molecule: This statement correctly describes plasmids. They are double-stranded, closed-loop DNA molecules without linear ends.
• They have antibiotic resistant genes: Plasmids frequently carry genes that provide beneficial functions, including resistance to antibiotics. This capability allows bacteria to survive exposure to drugs previously lethal.
• They have the ability of autonomous replication: This is another accurate characteristic of plasmids. They possess machinery for independent replication within the host cell, separate from chromosomal DNA replication.

Answer: Alec Jaffreys

DNA fingerprinting was first developed by Sir Alec Jaffreys. He pioneered the technique in the 1980s, and it has since become a powerful tool in forensic science, paternity testing, and genetic research. DNA fingerprinting involves analyzing specific regions of an individual’s DNA to create a unique identifier, much like a fingerprint.

The other options are incorrect:

• David Suzuki: While an accomplished Canadian geneticist and environmentalist, David Suzuki is not associated with the development of DNA fingerprinting. His research areas primarily focus on ecological genetics and conservation biology.
• Khorana: Har Gobind Khorana, an Indian-American biochemist, made significant contributions to understanding how genetic information is coded in DNA. However, his research mainly focused on deciphering the genetic code and did not involve the development of DNA fingerprinting technology.
• Gilbert: Walter Gilbert, an American physicist and biochemist, played a crucial role in deciphering the structure of DNA and developing early DNA sequencing methods. However, his groundbreaking work predates the development of DNA fingerprinting by Alec Jeffreys.

Answer: Plasmids are mobile.

Plasmids are mobile. Plasmids can move between bacterial cells, facilitating the transfer of genetic material. This mobility is often exploited in genetic engineering for the introduction of specific genes into bacteria.

The other options are incorrect:

• Plasmids are made up of RNA and proteins: Plasmids are solely composed of double-stranded DNA, not RNA or proteins. These components play crucial roles in cellular functions, but only DNA forms the backbone of plasmids.
• Plasmids are present in eukaryotes: While there are similar structures called episomes in some unicellular eukaryotes, true plasmids are not typically found in multicellular eukaryotes like plants and animals. Their genetic information is primarily stored in linear chromosomes within the nucleus.
• Plasmids are present in fungi: Although some fungi harbor yeast episomal plasmids (YEPs) resembling bacterial plasmids, true bacterial plasmids are not commonly found in fungi. YEPs have some similar properties but also differ in structure and function compared to typical bacterial plasmids.

Answer: All “RE” cut DNA at specific sites

Restriction Endonucleases (RE) is that they cut DNA at specific sites. Restriction endonucleases are enzymes that recognize specific DNA sequences, known as recognition sites or restriction sites, and cleave the DNA at or near these sequences. The cuts are precise and occur at specific locations.

The other options are incorrect:

• All “RE” cut DNA at random sites: This is incorrect. Each RE recognizes a unique, short sequence of nucleotides (typically 4-6 base pairs) and cleaves the DNA within that sequence. This targeted action makes them valuable tools for manipulating DNA molecules.
• All “RE” join DNA segments at specific sites: Although some REs possess limited cohesive end joining activity, their primary function is cleavage. They do not directly join DNA segments. This process usually involves DNA ligases, another type of enzyme.
• All “RE” join DNA at random sites: Similar to the previous point, DNA ligation by REs is not a common function. Additionally, joining DNA at random sites would not be beneficial for manipulating genetic material in a controlled manner.

Answer: Produced by gene transfer technology

Transgenic organisms are produced by gene transfer technology, where genes from one species are introduced into the genome of another species. This genetic modification allows the recipient organism to express traits or characteristics encoded by the transferred genes.

The other options are incorrect:

• Extinct organisms: While DNA analysis and sequencing can be used to study extinct organisms, this does not make them transgenic. Transgenic organisms are alive and modified with functional foreign genes.
• Naturally occurring and endemic: While some organisms contain naturally occurring genetic variations, transgenic organisms specifically involve the controlled introduction of genetic material from another organism, changing their original genetic makeup. Endemic species simply refer to those limited to a specific geographic region.
• Produced by traditional plant breeding technique: Traditional breeding relies on the crossing of existing organisms within a species or closely related species. It does not involve the direct transfer of DNA from unrelated organisms, which is the defining characteristic of transgenic organisms.

Answer: Host DNA is methylated hence restriction endonucleases can’t act.

Host DNA is methylated, and this methylation protects it from being cleaved by restriction endonucleases. The methylation of specific DNA sequences in the host genome prevents the restriction endonucleases from recognizing and cutting the host DNA, ensuring that they selectively act on foreign DNA.

The other options are incorrect:

• Restriction endonucleases cannot act on host DNA: This is not entirely true. REs can cleave host DNA, but only if the specific recognition sequence is present and not methylated.
• Host DNA is packed into chromosomes: While most host DNA is indeed packaged into chromosomes, REs can still access and cleave the recognition sequences within these structures.
• Restriction endonucleases become inactive when they reach host DNA: This is not the case. REs remain active and continue searching for their target sequences throughout the cell.

Answer: Arber

The presence of restriction endonucleases was postulated in 1960 by Werner Arber, a Swiss microbiologist. He observed that when bacteriophage DNA entered a bacterial cell, it was often degraded, suggesting the presence of enzymes specifically targeting foreign DNA. This observation laid the groundwork for the discovery and isolation of restriction enzymes, revolutionizing molecular biology and genetic engineering.

Incorrect Options:

• Khorana: Har Gobind Khorana, an Indian-American biochemist, made significant contributions to deciphering the genetic code, but his research did not involve the discovery of restriction enzymes.
• Watson and Crick: Francis Crick and James Watson are best known for their pioneering work on the structure of DNA. While their discovery was fundamental to understanding DNA mechanics, it did not directly lead to the discovery of restriction enzymes.
• Crick: Francis Crick, along with James Watson, is known for the discovery of the structure of DNA. However, he is not associated with the postulation of restriction endonucleases.

Answer: Smith, Nathans and Arber

The Nobel Prize in Physiology or Medicine for the discovery of restriction endonucleases was awarded jointly to Werner Arber, Daniel Nathans, and Hamilton Smith in 1978. These scientists made significant contributions to the understanding of these enzymes and their application in molecular biology and genetic engineering.

The other options are incorrect:

• Jacob and Monad: Francois Jacob and Jacques Monod received the Nobel Prize in Physiology or Medicine in 1965 for their discoveries regarding operons and gene regulation, not for restriction enzymes.
• Watson and Crick: As mentioned previously, Francis Crick and James Watson were recognized for their work on the structure of DNA, which laid the foundation for understanding DNA manipulation but did not directly involve restriction enzymes.
• Alec Jaffreys and Milstein: Alec Jeffreys and Cesar Milstein won the Nobel Prize in Chemistry in 1988 for their work on DNA fingerprinting and monoclonal antibodies, respectively, not for restriction enzymes.