Molecular Biology and Genomics Practice Questions

Q: In vitro DNA amplification is done by

Polymerase chain reaction. ***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.

Q: During eukaryotic protein synthesis, phosphorylation of which of the following is enhanced by insulin?

eIF4E. ***eIF4E*** - Insulin activates the **mTOR pathway**, which leads to activation of **Mnk1/2 kinases** that phosphorylate eIF4E at **Ser209**. - This phosphorylation enhances eIF4E's **affinity for the 5' cap structure** and increases **cap-dependent translation initiation** efficiency. *eIF4G* - While eIF4G is essential for **eIF4F complex formation**, its phosphorylation is not the primary target enhanced by insulin signaling. - Insulin's effect on eIF4G is mainly **indirect through 4E-BP1 phosphorylation**, which releases eIF4E to bind eIF4G. *eIF2* - **eIF2 phosphorylation** by kinases like **PERK, PKR, and GCN2** inhibits translation initiation during stress conditions. - This is **opposite to insulin's anabolic effects**, as insulin signaling typically promotes conditions that reduce eIF2 phosphorylation. *eIF4A* - eIF4A functions as an **RNA helicase** in the eIF4F complex, unwinding mRNA secondary structures. - While important for translation, **direct phosphorylation enhancement by insulin** is not a primary mechanism for eIF4A regulation.

Q: Larger DNA segments can be cloned in

Bacterial Artificial Chromosomes. ***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.

Q: Enzyme used in polymerase chain reaction is:

DNA polymerase. ***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.

Q: DNA amplification is done in:

PCR. ***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

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

Transposons. ***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.

Q: DNA amplification is done by all, except:

DNA sequencing. ***DNA sequencing*** - **DNA sequencing** determines the **nucleotide base order** in a DNA molecule but does not increase the amount of DNA. - While requiring a DNA template, it is an **analytical technique** rather than an amplification method. *Loop-mediated isothermal amplification (LAMP)* - **LAMP** is an **isothermal DNA amplification** technique that amplifies target DNA sequences at a constant temperature (60-65°C). - It uses a DNA polymerase with strand displacement activity and 4-6 primers to produce large amounts of DNA rapidly. *Ligase chain reaction* - **LCR** is an amplification method that detects specific **DNA sequences** by ligating adjacent probes. - It amplifies the signal from a target DNA sequence rather than the DNA itself by creating many copies of joined probes. *Polymerase chain reaction* - **PCR** is a widely used technique for **amplifying** a specific segment of DNA to produce many copies. - It involves cycles of **denaturation**, **annealing**, and **extension** using a DNA polymerase.

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

To screen for recombinant vectors. ***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.

Q: The first human protein produced by rDNA technology:

Insulin. ***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.

Q: Northern blotting used in separation and diagnosis of:

RNA. ***RNA*** - **Northern blotting** is a molecular biology technique used to detect specific **RNA sequences** in a sample. - It involves separating RNA fragments by size using gel electrophoresis, transferring them to a membrane, and then probing with a labeled complementary DNA or RNA sequence. *DNA* - **Southern blotting** is the technique specifically designed for the detection and analysis of specific **DNA sequences**. - While RNA can be used as a probe in Southern blotting, the primary target molecule for separation and diagnosis is DNA. *Histones* - **Histones** are proteins and are not typically targeted by Northern blotting, which is for nucleic acids. - Techniques like **Western blotting** or specific chromatin immunoprecipitation (ChIP) assays are used to study histones. *Proteins* - **Western blotting** is the technique used for the separation and detection of specific **proteins** in a sample. - Proteins are separated by size via SDS-PAGE, transferred to a membrane, and detected using specific antibodies.

Question 1

In vitro DNA amplification is done by

Accepted Answer

Polymerase chain reaction

Answer

Recombinant technique

Answer

Electrophoresis

Answer

Blotting technique

Question 2

During eukaryotic protein synthesis, phosphorylation of which of the following is enhanced by insulin?

Accepted Answer

eIF4E

Answer

eIF2

Answer

eIF4A

Answer

eIF4G

Question 3

Larger DNA segments can be cloned in

Accepted Answer

Bacterial Artificial Chromosomes

Answer

Plasmids

Answer

Cosmids

Answer

Bacteriophage

Question 4

Enzyme used in polymerase chain reaction is:

Accepted Answer

DNA polymerase

Answer

Restriction endonuclease

Answer

RNA polymerase

Answer

Alkaline phosphatase

Question 5

DNA amplification is done in:

Accepted Answer

PCR

Answer

Ligase chain reactions

Answer

NASBA (Nucleic Acid Sequence-Based Amplification)

Answer

All of the options

Question 6

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

Accepted Answer

Transposons

Answer

Cosmid

Answer

Episomes

Answer

Plasmid

Question 7

DNA amplification is done by all, except:

Accepted Answer

DNA sequencing

Answer

Loop-mediated isothermal amplification (LAMP)

Answer

Ligase chain reaction

Answer

Polymerase chain reaction

Question 8

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

Accepted Answer

To screen for recombinant vectors

Answer

To detect host DNA in situ

Answer

To detect gene mutations

Answer

To identify DNA inserts in plasmid vectors

Question 9

The first human protein produced by rDNA technology:

Accepted Answer

Insulin

Answer

Casein

Answer

Albumin

Answer

Growth hormone

Question 10

Northern blotting used in separation and diagnosis of:

Accepted Answer

RNA

Answer

DNA

Answer

Histones

Answer

Proteins

Molecular Biology and Genomics — MCQs

Molecular Biology and Genomics — MCQs

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