Recombinant DNA Technology — MCQs
What is Northern blot used to detect?
DNA transfer in bacteria by phage is:
R-factor in bacteria is transferred by:
Which of the following techniques is primarily used for RNA analysis?
Recombinant human insulin is made by -
Gene amplification is achieved through
Which one of the following enzymes is obtained from Thermus aquaticus bacterium that is heat stable and used in PCR at high temperature?
What is the most important tool used in genetic engineering?
Two transgenic plants were genetically engineered using Recombinant DNA technology. One plant was transformed using a plasmid vector with GFP (Green Fluorescent Protein) gene and another plant was transformed with a complete Luciferase bioluminescent system (including luciferase gene and luciferin substrate availability). Which of these two plants will glow spontaneously in the dark?
Which of the following is the least suitable source for DNA extraction?
Recombinant DNA Technology Indian Medical PG Practice Questions and MCQs
Question 1: What is Northern blot used to detect?
- A. Protein
- B. Immunoglobulin
- C. RNA (Correct Answer)
- D. DNA
Explanation: ***RNA*** - **Northern blot** is a laboratory technique used to detect specific **RNA** molecules among a mixture of RNA. - It involves separating RNA fragments by **gel electrophoresis**, transferring them to a membrane, and then probing with a labeled complementary sequence. *Protein* - **Proteins** are typically detected using a **Western blot**, which involves similar separation and transfer techniques but uses **antibodies** as probes. - While RNA codes for proteins, Northern blot *directly* detects RNA transcripts, not the resulting protein products. *Immunoglobulin* - **Immunoglobulins** (antibodies) are a type of protein, and their detection usually falls under **Western blot** or specific immunological assays like **ELISA**. - Northern blot is specifically designed for nucleic acid analysis, not protein detection. *DNA* - **DNA** is detected using a **Southern blot** technique, which also involves electrophoresis, transfer to a membrane, and hybridization with a complementary probe. - The name "Northern blot" was coined as a play on "Southern blot" because it uses similar methodology but for RNA instead of DNA.
Question 2: DNA transfer in bacteria by phage is:
- A. Transformation
- B. Conjugation
- C. Translation
- D. Transduction (Correct Answer)
Explanation: ***Transduction*** - **Transduction** is the process by which foreign DNA is introduced into a cell by a virus or viral vector, specifically a **bacteriophage** in bacteria. - During transduction, the phage infects a bacterial cell, and its genetic material becomes incorporated into the host cell's DNA, or it may package bacterial DNA into new phage particles, which then infect other bacteria. *Transformation* - **Transformation** is the process where bacteria take up **naked DNA** from their environment. - This process does not involve a bacteriophage or any other viral vector. *Conjugation* - **Conjugation** is a process of genetic transfer between bacterial cells involving direct cell-to-cell contact through a **pilus**. - It typically involves the transfer of plasmids or other genetic elements, not mediated by a bacteriophage. *Translation* - **Translation** is the process by which messenger RNA (mRNA) is decoded to produce a specific **amino acid sequence** (protein). - This is a fundamental step in gene expression and does not involve the transfer of DNA between bacteria via a phage.
Question 3: R-factor in bacteria is transferred by:
- A. Transduction
- B. Conjugation (Correct Answer)
- C. Uptake of naked DNA
- D. Genetic transfer from parent to offspring
Explanation: ***Conjugation*** - **R-factors** (resistance factors) are plasmids carrying genes for antibiotic resistance, and their primary mode of transfer between bacteria is through **conjugation**. - **Conjugation** involves direct cell-to-cell contact through a pilus, allowing the transfer of the plasmid DNA from a donor bacterium to a recipient bacterium. *Transduction* - **Transduction** involves the transfer of bacterial DNA by a **bacteriophage (virus)**, which can accidentally package bacterial genes instead of viral ones. - While it can transfer resistance genes, it is not the primary mechanism for R-factor spread across diverse bacterial species in the way conjugation is. *Uptake of naked DNA* - The **uptake of naked DNA** from the environment is known as **transformation**, which primarily occurs when bacteria are in a specific physiological state (competence). - This mechanism is less efficient for widespread R-factor dissemination compared to conjugation, which involves active transfer. *Genetic transfer from parent to offspring* - **Genetic transfer from parent to offspring** (vertical gene transfer) refers to the transmission of genetic material during cell division. - While R-factors are replicated and passed on to daughter cells, this does not explain their horizontal spread to new, unrelated bacteria.
Question 4: Which of the following techniques is primarily used for RNA analysis?
- A. Sanger's technique
- B. Western blot
- C. Next generation sequencing (Correct Answer)
- D. PCR
Explanation: ***Next generation sequencing*** - **Next-generation sequencing (NGS)**, particularly RNA-Seq, is widely used for **transcriptome analysis** to quantify and discover RNA molecules. - RNA-Seq allows for the precise measurement of **gene expression levels**, identification of **novel transcripts**, and detection of **splicing variants**. *Sanger's technique* - **Sanger sequencing** is primarily used for **DNA sequencing** to determine the exact order of nucleotides in a DNA molecule. - While it can be applied to cDNA (synthesized from RNA), it is not directly used for **RNA analysis** itself. *Western blot* - **Western blot** is a laboratory technique used to detect specific **proteins** in a sample. - It involves separating proteins by size using gel electrophoresis and then transferring them to a membrane for antibody-based detection, making it unsuitable for direct **RNA analysis**. *PCR* - **Polymerase Chain Reaction (PCR)** is used to amplify specific **DNA sequences**. - While **Reverse Transcription PCR (RT-PCR)** can quantify RNA by first converting it to cDNA, PCR itself does not directly analyze the RNA molecule.
Question 5: Recombinant human insulin is made by -
- A. cDNA of pancreatic cell (Correct Answer)
- B. cDNA from any eukaryote cell
- C. Genome of pancreatic cell
- D. Genome of any eukaryote
Explanation: ***CDNA of pancreatic cell*** - **Recombinant human insulin** is produced using **cDNA** (complementary DNA) synthesized from the **mRNA** of human pancreatic cells, as these cells naturally produce insulin. - This cDNA ensures that only the **coding sequences** for insulin are used, without introns, making it suitable for expression in prokaryotic hosts like *E. coli*. *CDNA from any eukaryote cell* - While insulin is a eukaryotic protein, using cDNA from "any eukaryote cell" would not be specific enough, as only **pancreatic islet beta cells** produce insulin. - Other eukaryotic cells do not express the insulin gene, so their cDNA would not contain the necessary genetic information. *Genome of pancreatic cell* - Although the **genome of a pancreatic cell** contains the insulin gene, it also includes **introns** (non-coding regions) that must be removed through splicing in eukaryotic cells. - If directly used in prokaryotic systems (like *E. coli*), which lack the machinery to remove introns, it would lead to an incorrect or non-functional protein. *Genome of any eukaryote* - Similar to "genome of pancreatic cell," using the **genome of any eukaryote** would be problematic due to the presence of introns and the general lack of the insulin gene in most eukaryotic cells. - This option combines the disadvantages of non-specificity and the presence of introns that are incompatible with prokaryotic expression systems.
Question 6: Gene amplification is achieved through
- A. Polymerase Chain Reaction (Correct Answer)
- B. DNA strand hybridization
- C. In situ DNA hybridization
- D. Ligase chain reaction (LCR)
Explanation: ***Polymerase Chain Reaction*** - **PCR** is the **gold standard** molecular biology technique that generates **millions to billions of copies** of a specific DNA segment over a short period. - It utilizes a cyclical process of **denaturation**, **annealing**, and **extension** with **thermostable DNA polymerase** to achieve exponential amplification. - **Most widely used** method for gene amplification in research and diagnostics. *DNA strand hybridization* - **DNA strand hybridization** is the process where two complementary single-stranded DNA molecules bind together to form a **double-stranded molecule**. - This process is fundamental to many molecular techniques but does not, in itself, achieve **amplification**; rather, it is a **binding event**. *In situ DNA hybridization* - **In situ hybridization** is a technique that localizes and detects specific **nucleic acid sequences** (DNA or RNA) within cells or tissues directly on a slide. - While it uses **hybridization**, its primary purpose is **detection and localization**, not the **amplification** of DNA sequences. *Ligase chain reaction (LCR)* - **LCR** is a molecular technique that does amplify DNA sequences exponentially using **DNA ligase** to join adjacent oligonucleotide probes. - However, it is **less commonly used** than PCR, has more **stringent requirements** (requires knowledge of both strands), and is primarily used for detecting **known point mutations** rather than general gene amplification. - **PCR remains the standard** technique when the question refers to gene amplification without additional qualifiers.
Question 7: Which one of the following enzymes is obtained from Thermus aquaticus bacterium that is heat stable and used in PCR at high temperature?
- A. DNA gyrase
- B. DNA polymerase III
- C. Taq polymerase (Correct Answer)
- D. Endonuclease
Explanation: ***Taq polymerase*** - This **heat-stable DNA polymerase** is isolated from the thermophilic bacterium *Thermus aquaticus*. - Its ability to withstand high temperatures makes it ideal for the **polymerase chain reaction (PCR)**, where DNA denaturation steps occur at elevated temperatures. *DNA gyrase* - **DNA gyrase** is a type II topoisomerase that introduces negative supercoils into DNA, which is important for DNA replication and transcription. - It is not heat-stable and is not directly used for DNA amplification in PCR. *DNA polymerase III* - **DNA polymerase III** is the primary enzyme responsible for DNA replication in *E. coli* and other bacteria. - It rapidly synthesizes DNA but is **not heat-stable** and would denature at the temperatures required for PCR. *Endonuclease* - **Endonucleases** are enzymes that cleave phosphodiester bonds within a polynucleotide chain. - While essential for processes like DNA repair and restriction mapping, they are not primarily involved in and are not heat-stable for DNA synthesis in PCR.
Question 8: What is the most important tool used in genetic engineering?
- A. Topoisomerase
- B. DNA Ligase
- C. Restriction endonuclease (Correct Answer)
- D. Helicase
Explanation: ***Restriction endonuclease*** - **Restriction endonucleases** are crucial for genetic engineering as they specifically cut DNA at particular recognition sites, allowing the insertion or deletion of genes. - This precise cutting ability is fundamental for creating **recombinant DNA** molecules. *Helicase* - **Helicase** is primarily involved in unwinding the DNA double helix during processes like DNA replication and transcription. - While essential for cellular functions, it does not directly manipulate DNA for gene insertion or modification in the way restriction enzymes do. *Topoisomerase* - **Topoisomerase** enzymes are responsible for managing DNA supercoiling, preventing tangling during DNA replication and transcription by cutting and rejoining DNA strands. - It plays a role in DNA structure but is not directly used for targeted gene editing or insertion. *DNA Ligase* - **DNA ligase** is essential for joining DNA fragments, which is a critical step in genetic engineering after restriction endonucleases have cut the DNA. - However, while it acts as a "molecular glue" to seal nicks and re-form phosphodiester bonds, it cannot initiate the precise cutting required to isolate genes.
Question 9: Two transgenic plants were genetically engineered using Recombinant DNA technology. One plant was transformed using a plasmid vector with GFP (Green Fluorescent Protein) gene and another plant was transformed with a complete Luciferase bioluminescent system (including luciferase gene and luciferin substrate availability). Which of these two plants will glow spontaneously in the dark?
- A. Plant with Luciferase Gene (Correct Answer)
- B. Both plants
- C. Plant with GFP Gene
- D. None of the options
Explanation: ***Plant with Luciferase Gene*** - The plant transformed with the **complete bioluminescent system**, including the **luciferase gene** and **luciferin substrate**, will glow spontaneously because luciferase acts on luciferin to produce light through a chemical reaction. - The question explicitly states "complete Luciferase bioluminescent system (including luciferase gene and luciferin substrate availability)," indicating all necessary components for bioluminescence are present. - **Bioluminescence** is light produced by living organisms through chemical reactions, requiring both enzyme (luciferase) and substrate (luciferin). *Both plants* - This is incorrect because the plant with the **GFP gene** alone will not glow spontaneously in the dark. - GFP requires **excitation by an external light source** (e.g., UV or blue light) to fluoresce, so it cannot contribute to spontaneous glowing. - Only the luciferase-transformed plant produces light spontaneously. *Plant with GFP Gene* - **GFP** (Green Fluorescent Protein) is **fluorescent**, not bioluminescent; it absorbs light at one wavelength and emits it at another wavelength. - GFP does not generate its own light in the dark and requires **illumination with an appropriate light source** (blue or ultraviolet light) to excite the protein and produce visible fluorescence. - Without external light excitation, GFP remains invisible in darkness. *None of the options* - This is incorrect because the plant equipped with a **complete luciferase bioluminescent system** is specifically designed to produce light spontaneously. - All required components (luciferase enzyme and luciferin substrate) are present and functional, enabling autonomous light production in the dark.
Question 10: Which of the following is the least suitable source for DNA extraction?
- A. CSF (Correct Answer)
- B. Hair roots
- C. Semen
- D. Buccal mucosa
Explanation: ***CSF*** - **Cerebrospinal fluid (CSF)** contains a relatively **low number of cells**, making it a poor source for DNA extraction compared to other bodily fluids due to the scarcity of nuclear DNA. - While DNA can be extracted from CSF for specific diagnostic purposes (e.g., detection of pathogens), it is generally **not the preferred source** for DNA profiling or genetic studies due to the limited yield and potential for degradation. *Hair roots* - **Hair roots** (specifically the follicular tag) contain a significant number of **nucleated cells**, making them an excellent source for DNA extraction. - The DNA extracted from hair roots is often robust and sufficient for **forensic analysis** and genetic testing. *Semen* - **Semen** contains a high concentration of **sperm cells**, which are rich in nuclear DNA, making it a very good source for DNA extraction. - It is frequently used in **forensic investigations** and paternity testing due to its high DNA content. *Buccal mucosa* - **Buccal cells** scraped from the inside of the cheek provide a non-invasive and **abundant source of nucleated cells** for DNA extraction. - This method is widely used for genetic testing, **ancestry tracing**, and clinical diagnostics because of its ease of collection and high DNA yield.
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