Molecular Biology and Genomics — MCQs

Molecular Biology and Genomics Indian Medical PG Practice Questions and MCQs

Question 771: The mobile genetic elements that can move between chromosomal and extrachromosomal DNA molecules within cells are -

A. Cosmid
B. Episomes
C. Plasmid
D. Transposons (Correct Answer)

Explanation: ***Transposons*** - **Transposons**, also known as "jumping genes," are segments of DNA that can **move independently** from one location to another within a genome, including between chromosomal and extrachromosomal DNA. - They achieve this movement through two main mechanisms: **"cut-and-paste"** (DNA transposons) or **"copy-and-paste"** (retrotransposons). *Cosmid* - A **cosmid** is a hybrid plasmid that contains **cos sequences** (cohesive ends) from lambda phage, enabling it to package large DNA fragments (up to 45 kb) for cloning. - While it can exist as an extrachromosomal element, it is primarily a **cloning vector** and does not inherently move and integrate into chromosomal DNA like a transposon. *Episomes* - **Episomes** are a type of plasmid that can **replicate autonomously** (extrachromosomal) or **integrate into the host chromosome**. - While they can move between these states, the term "mobile genetic elements that move between chromosomal and extrachromosomal DNA molecules" more precisely describes the **active transposition** mechanism of transposons, which relocate specific DNA segments, rather than an entire replicon like an episome. *Plasmid* - A **plasmid** is a small, extrachromosomal DNA molecule within a cell that is **physically separate** from chromosomal DNA and can replicate independently. - Plasmids are typically stable extrachromosomal elements and generally do not inherently possess the machinery to **integrate into** or **excise from** the host chromosome like transposons do.

Question 772: In molecular cloning, blue-white screening is used for:

A. To detect host DNA in situ
B. To detect gene mutations
C. To screen for recombinant vectors (Correct Answer)
D. To identify DNA inserts in plasmid vectors

Explanation: ***To screen for recombinant vectors*** - **Blue-white screening** is the standard method to differentiate between **recombinant plasmids** (containing an insert) and **non-recombinant plasmids** (self-ligated without insert) in bacterial colonies. - The technique relies on insertional inactivation of the **lacZ gene** in the cloning vector. When foreign DNA is successfully inserted into the multiple cloning site within lacZ, the gene is disrupted. - In the presence of **X-gal** (substrate) and **IPTG** (inducer), colonies with non-recombinant plasmids produce functional **β-galactosidase** enzyme, which cleaves X-gal to produce a **blue color**. - Colonies with recombinant plasmids cannot produce functional β-galactosidase due to the disrupted lacZ gene, resulting in **white colonies**. - This allows researchers to easily identify and select recombinant clones for further analysis. *To identify DNA inserts in plasmid vectors* - While blue-white screening does indicate the presence of a DNA insert, this phrasing is less precise than "screening for recombinant vectors," which is the established terminology. - The method identifies successful cloning events but does not characterize the nature, source, or identity of the inserted DNA. - Further analysis (restriction mapping, sequencing) is needed to confirm the insert is the desired fragment. *To detect gene mutations* - Blue-white screening does not detect mutations in genes; it detects insertional inactivation of the lacZ gene. - While lacZ disruption could be considered a type of mutation, the purpose is to identify successful DNA insertion events, not to screen for spontaneous or induced mutations. *To detect host DNA in situ* - This is incorrect. Blue-white screening does not detect host chromosomal DNA or perform in situ detection. - The assay is based on plasmid-borne lacZ gene activity in transformed bacterial colonies, not on detecting host genomic DNA.

Question 773: The first human protein produced by rDNA technology:

A. Casein
B. Albumin
C. Growth hormone
D. Insulin (Correct Answer)

Explanation: ***Insulin*** - **Recombinant DNA (rDNA) technology** enabled the production of human insulin in bacteria, specifically *E. coli*, in 1978. - This breakthrough provided a sustainable and safer source of insulin for treating **diabetes**, replacing animal-derived forms. *Casein* - **Casein** is a family of phosphoproteins found in mammalian milk and is not a protein typically produced via initial rDNA technology for therapeutic human use. - Its primary role is nutritional, serving as a significant source of **amino acids**, calcium, and phosphate in milk. *Albumin* - **Albumin** is a major protein in human plasma, but its initial production through rDNA technology for therapeutic purposes came significantly later than insulin. - Though now produced recombinantly, early efforts focused on proteins like insulin with more immediate and widespread clinical demand. *Growth hormone* - **Human growth hormone (hGH)** was also an early target for rDNA technology and was successfully produced in bacteria in the early 1980s. - However, human insulin recombinant production occurred *before* growth hormone, making insulin the **first human protein** produced through this method.

Question 774: Retrovirus is used for gene therapy because -

A. They integrate stably into human genome (Correct Answer)
B. They have sequences common to human genome
C. Easy to perform in labs
D. Economically viable

Explanation: ***They integrate stably into human genome*** - **Retroviruses** are favored in gene therapy because they possess the enzyme **reverse transcriptase**, allowing them to convert their RNA genome into DNA. - This DNA can then be efficiently and **stably integrated** into the host cell's **chromosomal DNA**, ensuring long-term expression of the therapeutic gene. - The stable integration provides permanent correction in dividing cells, making it ideal for treating genetic disorders. *They have sequences common to human genome* - While retroviruses can integrate into the human genome, their advantage in gene therapy is not due to having naturally common sequences with humans. - The integration mechanism is enzyme-driven, not sequence homology-driven, for therapeutic effect. *Easy to perform in labs* - While retroviral vectors are widely used, their manipulation requires significant biosafety measures and expertise, making them not inherently "easy to perform." - The primary advantage lies in their biological properties, not their laboratory handling simplicity. *Economically viable* - Gene therapy, especially using viral vectors, is a complex and highly regulated process, making it one of the most expensive medical treatments. - The economic viability is not a primary reason for choosing retroviruses; rather, their therapeutic efficacy drives their use despite the cost.

Question 775: In molecular biology, λ (lambda) phage is commonly used as a cloning vector. Which symbol correctly represents lambda?

A. β
B. λ (Correct Answer)
C. α
D. None of the options

Explanation: ***Correct: λ*** - **Lambda (λ)** is the correct Greek letter symbol for lambda - **Lambda phage** is a bacteriophage commonly used as a **cloning vector in molecular biology** and genetic engineering - It has been instrumental in **recombinant DNA technology** and gene cloning experiments - Lambda phage can accommodate **DNA inserts of 15-23 kb**, making it useful for genomic library construction *Incorrect: β (Beta)* - Beta is a different Greek letter - In biochemistry, β commonly denotes **beta-sheets** in protein secondary structure or **beta-oxidation** of fatty acids - Not the symbol for lambda *Incorrect: α (Alpha)* - Alpha is a different Greek letter - In biochemistry, α typically represents **alpha-helices** in proteins or **alpha-amino acids** - Not the symbol for lambda *Incorrect: None of the options* - The correct symbol (λ) is present among the options

Question 776: True about polymerase chain reaction is:

A. Enzymatic DNA amplification (Correct Answer)
B. Non-enzymatic DNA amplification
C. Recombinant DNA amplification
D. Separation of protein fragments in serum

Explanation: ***Enzymatic DNA amplification*** - **Polymerase Chain Reaction (PCR)** is a molecular biology technique that uses an **enzyme**, DNA polymerase (Taq polymerase), to rapidly make millions to billions of copies of a specific **DNA segment** - The process involves cycles of denaturing the DNA (95°C), annealing primers (50-65°C), and extending the primers using **heat-stable DNA polymerase**, thus amplifying the target DNA exponentially - Each cycle doubles the amount of target DNA, resulting in **exponential amplification** *Non-enzymatic DNA amplification* - PCR is fundamentally an **enzymatic process** that requires DNA polymerase enzyme - Non-enzymatic methods of DNA amplification do not represent PCR technology - The heat-stable **Taq polymerase** is essential for the repeated thermal cycling *Recombinant DNA amplification* - **Recombinant DNA technology** involves combining DNA from different sources, often for gene cloning or genetic engineering, which is distinct from PCR's primary function - While PCR can be used to amplify recombinant DNA sequences, the technique itself is not defined as recombinant DNA amplification - PCR simply amplifies **existing DNA sequences** without creating recombinant molecules *Separation of protein fragments in serum* - This describes techniques like **electrophoresis** (SDS-PAGE) or chromatography, used to separate proteins based on size or charge - PCR deals specifically with **DNA amplification** and does not involve protein separation - This is a completely different molecular biology technique

Question 777: Which of the following is an anti-apoptotic gene?

A. c-myc
B. p53
C. Bcl-2 (Correct Answer)
D. Bax

Explanation: ***Bcl-2*** - **Bcl-2** (B-cell lymphoma 2) is a proto-oncogene that plays a critical role in regulating **apoptosis** by inhibiting programmed cell death. - It prevents the release of pro-apoptotic factors from the mitochondria, thereby promoting **cell survival**. *c-myc* - **c-myc** is a proto-oncogene involved in cell proliferation, growth, and **apoptosis**; it is not primarily an anti-apoptotic gene. - Upregulation of c-myc can, in fact, sensitize cells to **apoptosis** if survival signals are absent. *p53* - **p53** is a tumor suppressor gene that induces cell cycle arrest or **apoptosis** in response to DNA damage or other cellular stresses. - It is a **pro-apoptotic** gene that actively promotes programmed cell death, rather than preventing it. *Bax* - **Bax** (Bcl-2-associated X protein) is a prominent **pro-apoptotic** protein. - It promotes **apoptosis** by forming pores in the mitochondrial outer membrane, leading to the release of cytochrome c and activation of caspases.

Question 778: The primary structure of a protein is determined by:

A. Hydrogen bonds.
B. Disulfide bonds.
C. Amino acid sequence. (Correct Answer)
D. Hydrophobic interactions.

Explanation: ***Amino acid sequence*** - The **primary structure** of a protein is defined as the **linear sequence of amino acids** connected by **peptide bonds**. - This sequence is determined by the **genetic code** (DNA → mRNA → protein) and dictates all higher-order structures. - The primary structure is the fundamental level of protein organization and determines the protein's unique properties and function. - Any change in the amino acid sequence (mutation) can alter protein function, as seen in diseases like sickle cell anemia (single amino acid substitution in hemoglobin). *Hydrogen bonds* - Hydrogen bonds are involved in **secondary structure** (α-helix and β-pleated sheet) and **tertiary structure** stabilization. - They form between the backbone carbonyl oxygen and amide hydrogen atoms, not determining the sequence itself. - While important for protein folding, they do not define primary structure. *Disulfide bonds* - Disulfide bonds (covalent bonds between cysteine residues) contribute to **tertiary** and **quaternary structure** stability. - They form after the protein is synthesized and help maintain the 3D conformation. - They are post-translational modifications, not determinants of the primary amino acid sequence. *Hydrophobic interactions* - Hydrophobic interactions are non-covalent forces that drive **tertiary structure** formation by causing nonpolar amino acids to cluster in the protein core. - They contribute to protein folding and stability but do not determine the sequence of amino acids. - These are weak interactions that occur after the primary structure is established.

Question 779: Transgenic animals are:

A. Genetically modified organisms with a new heritable character
B. Serve as models for understanding human diseases
C. All of the options (Correct Answer)
D. Proteins produced by them are used as therapeutic agents

Explanation: ***Correct Answer: All of the options*** All three statements about transgenic animals are correct, making "All of the options" the right answer. **Why each statement is TRUE:** **Genetically modified organisms with a new heritable character** ✓ - Transgenic animals have **foreign DNA (transgene)** stably integrated into their genome - This genetic modification is **heritable** and passed to offspring - This is the fundamental definition of a transgenic organism **Serve as models for understanding human diseases** ✓ - Transgenic animal models (especially mice) are engineered to mimic **human genetic diseases** - Examples include models for Alzheimer's disease, cancer, diabetes, and cardiovascular disorders - These models are crucial for understanding disease mechanisms and testing potential therapies **Proteins produced by them are used as therapeutic agents** ✓ - Transgenic animals act as **bioreactors** producing recombinant proteins - Process called **molecular pharming** or **biopharming** - Examples: therapeutic antibodies, clotting factors (Factor VIII, Factor IX), hormones, produced in milk, blood, or other fluids - These proteins have important clinical applications in treating human diseases Since all three individual statements are accurate and represent different aspects/applications of transgenic animals, the comprehensive answer is "All of the options."

Question 780: DNA fingerprinting is used for paternity testing and forensic identification of suspects. Which of the following is the most accurate description of DNA fingerprinting?

A. DNA is isolated from blood, skin, or sperm and its fragment size distribution is analyzed by gel electrophoresis
B. DNA can be isolated from blood, skin, or sperm and analyzed for variable patterns of restriction fragments arising from tandemly repeated sequences (microsatellites) (Correct Answer)
C. DNA is isolated from blood, skin, or sperm and hybridized with probes from the HLA locus to visualize HLA gene patterns
D. DNA is copied from blood, skin, or sperm RNA using reverse transcriptase and analyzed for the pattern of complementary DNAs

Explanation: ***DNA can be isolated from blood, skin, or sperm and analyzed for variable patterns of restriction fragments arising from tandemly repeated sequences (microsatellites)*** - **DNA fingerprinting**, also known as **DNA profiling**, primarily relies on the analysis of highly variable regions of DNA, specifically **tandemly repeated sequences** like microsatellites or STRs (short tandem repeats). - These regions exhibit individual-specific variation in the number of repeats, which, when cut by **restriction enzymes**, produce fragments of varying lengths, generating a unique **restriction fragment length polymorphism (RFLP)** pattern. *DNA is isolated from blood, skin, or sperm and its fragment size distribution is analyzed by gel electrophoresis* - While **gel electrophoresis** is a part of the process to separate DNA fragments by size, this option is incomplete as it doesn't specify *what* fragments are being analyzed or *why* they differ between individuals. - The crucial aspect of DNA fingerprinting is the analysis of **variable short tandem repeats (STRs)** or **variable number tandem repeats (VNTRs)**, which generate these distinct fragment sizes. *DNA is isolated from blood, skin, or sperm and hybridized with probes from the HLA locus to visualize HLA gene patterns* - **HLA (Human Leukocyte Antigen)** typing is used for tissue matching in transplantation and for studying autoimmune diseases, but it is **not the primary method** for DNA fingerprinting in paternity or forensic cases. - While HLA genes are polymorphic, the specific patterns examined in DNA fingerprinting are typically **non-coding repetitive sequences** which are more variable and less complex to interpret for individual identification. *DNA is copied from blood, skin, or sperm RNA using reverse transcriptase and analyzed for the pattern of complementary DNAs* - **DNA fingerprinting** directly analyzes **genomic DNA**, not RNA. The process of reverse transcribing RNA into cDNA is typically used for studying gene expression. - **RNA is less stable** than DNA and does not contain the same highly variable **repetitive sequences** (like STRs or VNTRs) that are fundamental to DNA fingerprinting.

Practice by Chapter

DNA Replication and Repair Mechanisms

Practice Questions

Transcription Factors and Gene Regulation

Practice Questions

Epigenetics and DNA Methylation

Practice Questions

RNA Processing and Splicing

Practice Questions

miRNA and RNA Interference

Practice Questions

Protein Synthesis and Post-Translational Modifications

Practice Questions

Genomics and Human Genome Project

Practice Questions

Single Nucleotide Polymorphisms

Practice Questions

Gene Therapy Approaches

Practice Questions

CRISPR-Cas9 and Genome Editing

Practice Questions

DNA Fingerprinting and Forensics

Practice Questions

Molecular Basis of Genetic Diseases

Practice Questions

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