Molecular Biology and Genomics — MCQs

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?

Q766

Which of the following statements is false regarding transposons?

Q767

In vitro DNA amplification is done by

Q768

Larger DNA segments can be cloned in

Q769

Enzyme used in polymerase chain reaction is:

Q770

DNA amplification is done in:

Molecular Biology and Genomics Indian Medical PG Practice Questions and MCQs

Question 761: All are added to PCR, except:

A. Thermostable DNA polymerase
B. Template DNA
C. Deoxynucleotide
D. Dideoxynucleotide (Correct Answer)

Explanation: ***Dideoxynucleotide*** - **Dideoxynucleotides (ddNTPs)** are chain-terminating nucleotides that lack a 3'-hydroxyl group, preventing further phosphodiester bond formation and DNA strand elongation. They are primarily used in **Sanger sequencing**, not standard PCR. - In PCR, the goal is to amplify DNA segments, which requires continued strand synthesis, making ddNTPs unsuitable as they would halt the amplification process. *Thermostable DNA polymerase* - **Thermostable DNA polymerase** (e.g., Taq polymerase) is a crucial component of PCR, responsible for synthesizing new DNA strands during the extension phase. - Its thermostability allows it to withstand the high temperatures used during the denaturation step in each cycle without losing activity. *Template DNA* - **Template DNA** is the specific DNA sequence that needs to be amplified, serving as the blueprint for the PCR reaction. - The primers anneal to the template DNA, dictating the region that will be copied. *Deoxynucleotide* - **Deoxynucleotides (dNTPs)** are the basic building blocks of DNA (dATP, dCTP, dGTP, dTTP) that are incorporated by DNA polymerase to synthesize new DNA strands. - They provide the raw materials for the "extension" phase of PCR, where the DNA polymerase adds nucleotides complementary to the template strand.

Question 762: Restriction fragment length polymorphism is used for:

A. Detection of gene mutations
B. Genetic mapping and identification (Correct Answer)
C. Paternity testing
D. Forensic analysis

Explanation: ***Genetic mapping and identification*** - **Restriction fragment length polymorphism (RFLP)** exploits variations in DNA sequences that create or abolish **restriction enzyme recognition sites**, leading to fragments of different lengths. - These polymorphic fragments serve as **genetic markers** to map genes on chromosomes and identify specific genes or genetic regions. *Detection of gene mutations* - While RFLP can detect some mutations by altering restriction sites, it is not the primary or most efficient method for general **gene mutation detection**. - Techniques like **DNA sequencing** or **PCR-based assays** are typically more sensitive and comprehensive for direct mutation analysis. *Paternity testing* - RFLP was historically used for **paternity testing** by comparing inheritance patterns of polymorphic markers between child and alleged father. - However, it has largely been replaced by more advanced and faster methods like **short tandem repeat (STR) analysis** due to higher discriminatory power and lower DNA requirements. *Forensic analysis* - Similar to paternity testing, RFLP was an early technique employed in **forensic analysis** for DNA fingerprinting to identify individuals. - Modern forensic DNA analysis predominantly uses **STR profiling**, which offers greater resolution, speed, and requires smaller, less degraded samples.

Question 763: PCR is primarily a

A. DNA sequencing technique
B. All of these
C. DNA degradation technique
D. DNA amplification technique (Correct Answer)

Explanation: ***Correct: DNA amplification technique*** - **Polymerase Chain Reaction (PCR)** is a laboratory technique used to make millions of copies of a specific DNA segment - This amplification allows for easier detection, analysis, and manipulation of even very small amounts of DNA - PCR uses repeated cycles of heating and cooling with DNA polymerase to exponentially amplify target DNA sequences *Incorrect: DNA sequencing technique* - **DNA sequencing** determines the exact order of nucleotides within a DNA molecule, which is different from PCR's primary function - While PCR products can be sequenced afterward, PCR itself does not determine the nucleotide sequence - Sequencing is a separate technique (e.g., Sanger sequencing, Next-generation sequencing) *Incorrect: DNA degradation technique* - **DNA degradation** involves the breakdown of DNA molecules, typically by nucleases or chemical/physical processes - PCR's purpose is to **synthesize and increase** the amount of DNA, not to break it down - This is the opposite of what PCR does *Incorrect: All of these* - PCR has a specific primary function: **DNA amplification** - It is not a combination of amplification, sequencing, and degradation techniques - While PCR can be part of a workflow that includes sequencing, its primary role is amplification only

Question 764: ChIP is used for :

A. Movement of proteins
B. Protein DNA interactions and histone modifications (Correct Answer)
C. Study of aneuploidy
D. Amplify DNA

Explanation: ***Protein DNA interactions and histone modifications*** - **Chromatin immunoprecipitation (ChIP)** is a molecular biology technique used to investigate the **interaction of specific proteins with DNA**. - It allows for the identification of DNA regions bound by a particular protein, including **transcription factors** and **histone modification patterns**. *Movement of proteins* - Techniques like **fluorescence recovery after photobleaching (FRAP)** or **single-particle tracking** are used to study the movement of proteins. - ChIP is primarily focused on the physical binding of proteins to DNA, not their dynamic movement within a cell. *Study of aneuploidy* - **Aneuploidy**, which is an abnormal number of chromosomes, is typically studied using techniques such as **karyotyping**, **FISH (fluorescence in situ hybridization)**, or **comparative genomic hybridization (CGH)**. - ChIP does not directly assess chromosomal number or large-scale chromosomal aberrations. *Amplify DNA* - **Polymerase Chain Reaction (PCR)** is the primary method used to **amplify DNA** sequences. - While ChIP often concludes with PCR to analyze the immunoprecipitated DNA, its core purpose is not amplification itself but rather the isolation of protein-bound DNA.

Question 765: 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 766: Which of the following statements is false regarding transposons?

A. The ends of transposons carry 'inverted repeat' sequences
B. They are also known as "jumping genes"
C. It was first discovered by Barbara McClintock
D. Long transposons are known as insertion sequences (Correct Answer)

Explanation: ***Long transposons are known as insertion sequences*** ✓ **This is the FALSE statement** - **Insertion sequences (IS elements)** are actually the **shortest** type of transposons, typically 700-2500 bp in length - They contain only the genes necessary for transposition (transposase) and inverted terminal repeats - **Complex (composite) transposons** are the **longer** elements that contain additional genes (e.g., antibiotic resistance) beyond those required for transposition - This statement reverses the relationship: IS elements are short, not long *The ends of transposons carry 'inverted repeat' sequences* - **TRUE statement** - All transposons are flanked by **inverted terminal repeats (ITRs)**, typically 9-40 bp in length - These sequences are recognized by the **transposase enzyme**, which catalyzes the transposition process - ITRs are essential structural features for both cut-and-paste and replicative transposition mechanisms *They are also known as "jumping genes"* - **TRUE statement** - This is the colloquial term coined to describe the **mobility** of these genetic elements - Transposons can **"jump"** from one chromosomal location to another, either by cut-and-paste or copy-and-paste mechanisms - This mobility can cause mutations, chromosomal rearrangements, and changes in gene expression *It was first discovered by Barbara McClintock* - **TRUE statement** - **Barbara McClintock** discovered transposable elements in **maize (corn)** in the **1940s-1950s** - She called them "controlling elements" due to their effects on gene expression - Her groundbreaking work was recognized with the **Nobel Prize in Physiology or Medicine in 1983** - This discovery revolutionized genetics by showing that genomes are dynamic rather than static

Question 767: In vitro DNA amplification is done by

A. Recombinant technique
B. Polymerase chain reaction (Correct Answer)
C. Electrophoresis
D. Blotting technique

Explanation: ***Polymerase chain reaction*** - **Polymerase chain reaction (PCR)** is an in vitro technique used to amplify specific DNA sequences, creating millions of copies from a small initial sample. - It involves cycles of **denaturation** (94-96°C), **annealing** (50-65°C), and **extension** (72°C) using a heat-stable DNA polymerase like **Taq polymerase**. - PCR is the gold standard for in vitro DNA amplification, requiring only a **thermocycler**, primers, dNTPs, and DNA polymerase. *Recombinant technique* - **Recombinant DNA technology** involves combining DNA from different sources to create new genetic material for gene expression or cloning. - It utilizes **restriction enzymes** and **ligases** to insert DNA into vectors, which are then replicated within **host organisms** (bacteria, yeast) - this is primarily an **in vivo** process, not in vitro amplification. *Electrophoresis* - **Electrophoresis** is a separation technique used to resolve DNA fragments, RNA, or proteins based on size and charge through a gel matrix. - It does not amplify DNA; it's used for **analysis** and **visualization** of DNA samples after amplification or other manipulations. *Blotting technique* - **Blotting techniques** (Southern blot for DNA, Northern blot for RNA, Western blot for proteins) detect specific macromolecules after gel electrophoresis. - These methods transfer molecules to membranes and use labeled probes for **identification and detection**, not amplification.

Question 768: Larger DNA segments can be cloned in

A. Plasmids
B. Cosmids
C. Bacteriophage
D. Bacterial Artificial Chromosomes (Correct Answer)

Explanation: ***Bacterial Artificial Chromosomes*** - **Bacterial Artificial Chromosomes (BACs)** are engineered to carry very large DNA inserts, typically ranging from **100 to 300 kilobases (kb)**, making them suitable for cloning large genomic fragments. - They are based on the **F-plasmid** of *E. coli*, which ensures stable maintenance and replication of large DNA segments in bacterial cells. *Plasmids* - **Plasmids** are small, circular DNA molecules commonly used as cloning vectors, but they have a limited capacity, typically accepting inserts of **up to 10-15 kb**. - Their small size makes them easy to work with in labs, but insufficient for cloning very large genomic segments. *Cosmids* - **Cosmids** are hybrid vectors combining features of plasmids and bacteriophage lambda, allowing them to carry larger DNA inserts than standard plasmids, usually between **30-45 kb**. - They are useful for cloning moderately large DNA fragments but are still not as efficient as BACs for extremely large segments. *Bacteriophage* - **Bacteriophage lambda** vectors can accommodate DNA inserts ranging from **10-25 kb**, which is larger than plasmids but smaller than BACs. - They are primarily used for generating **genomic libraries** for organisms with smaller genomes and are less suitable for cloning very large eukaryotic DNA.

Question 769: Enzyme used in polymerase chain reaction is:

A. Restriction endonuclease
B. RNA polymerase
C. Alkaline phosphatase
D. DNA polymerase (Correct Answer)

Explanation: ***DNA polymerase*** - **DNA polymerase** is essential for **polymerase chain reaction (PCR)** as it synthesizes new DNA strands using the target DNA as a template. - The enzyme used in PCR (e.g., **Taq polymerase**) is heat-stable and can withstand the denaturation steps of the reaction. *Restriction endonuclease* - **Restriction endonucleases** recognize and cut DNA at specific nucleotide sequences, a process used in **gene cloning** and **DNA fingerprinting**, not PCR amplification. - Their primary role is in **molecular cloning** and **gene editing**, where precise DNA cleavage is required. *RNA polymerase* - **RNA polymerase** transcribes DNA into RNA, a process known as **transcription**, and is not directly involved in the DNA replication steps of PCR. - It is crucial for **gene expression** and protein synthesis but not for amplifying DNA in vitro. *Alkaline phosphatase* - **Alkaline phosphatase** removes phosphate groups from molecules, often used in molecular biology to **dephosphorylate DNA** or RNA ends. - It prevents **self-ligation** in cloning experiments but has no role in the amplification process of PCR.

Question 770: DNA amplification is done in:

A. PCR (Correct Answer)
B. Ligase chain reactions
C. NASBA (Nucleic Acid Sequence-Based Amplification)
D. All of the options

Explanation: ***Correct: PCR*** - **Polymerase Chain Reaction (PCR)** is the gold standard technique for DNA amplification in molecular diagnostics and research - Uses **DNA polymerase** (typically Taq polymerase) to exponentially amplify specific DNA sequences through thermal cycling - Involves repeated cycles of **denaturation, annealing, and extension** using primers, dNTPs, and thermostable polymerase - Can generate **millions of copies** from a single DNA template in hours *Incorrect: Ligase chain reactions* - **Ligase Chain Reaction (LCR)** is a technique that uses **DNA ligase** to join adjacent oligonucleotide probes that hybridize to a target sequence - While LCR can amplify DNA through exponential ligation cycles, it is primarily used for **detection of known point mutations** and SNPs rather than general DNA amplification - Requires **four primers** (two for each strand) and perfect complementarity at ligation junctions - Less commonly used than PCR for routine DNA amplification in clinical practice *Incorrect: NASBA (Nucleic Acid Sequence-Based Amplification)* - **NASBA** is an **isothermal RNA amplification** technique that operates at a constant temperature (41°C) - Specifically designed to amplify **RNA targets** using reverse transcriptase, RNase H, and T7 RNA polymerase - Produces single-stranded RNA products, not double-stranded DNA like PCR - Used primarily for **RNA virus detection** (HIV, HCV) and gene expression analysis, not for DNA amplification *Incorrect: All of the options* - While LCR technically can amplify DNA, **PCR is the standard method** for DNA amplification in molecular biology - NASBA is designed for RNA, not DNA amplification - In the context of medical education and clinical practice, **PCR is the definitive answer** for DNA amplification

Practice by Chapter

DNA Replication and Repair Mechanisms

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Transcription Factors and Gene Regulation

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Epigenetics and DNA Methylation

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RNA Processing and Splicing

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miRNA and RNA Interference

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Protein Synthesis and Post-Translational Modifications

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Genomics and Human Genome Project

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Single Nucleotide Polymorphisms

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Gene Therapy Approaches

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CRISPR-Cas9 and Genome Editing

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DNA Fingerprinting and Forensics

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Molecular Basis of Genetic Diseases

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