Molecular Biology and Genomics Practice Questions

Q: Retrovirus is used for gene therapy because -

They integrate stably into human genome. ***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.

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

λ. ***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

Q: True about polymerase chain reaction is:

Enzymatic DNA amplification. ***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

Q: Increasing severity of intellectual disability of male members over generations is a result of ?

Trinucleotide repeat mutation. ***Trinucleotide repeat mutation*** - This phenomenon, known as **anticipation**, is characteristic of disorders caused by trinucleotide repeat expansions like **Fragile X syndrome**, where the number of repeats increases in successive generations, leading to earlier onset and more severe symptoms. - The expansion of these repeats often occurs during **meiosis**, particularly **oogenesis** for Fragile X, contributing to the increasing severity observed in offspring. *Y linked disorder* - Y-linked disorders affect only males and are passed from father to son, but they do not typically show increasing severity over generations or the phenomenon of anticipation. - Their inheritance pattern is straightforward and generally consistent across generations, without progressive phenotypic changes. *Frameshift mutation* - A **frameshift mutation** involves the insertion or deletion of nucleotides that are not multiples of three, leading to a shift in the reading frame and an altered protein sequence. - While they can cause severe genetic disorders, **frameshift mutations** do not typically explain the observed increase in severity across generations (anticipation). *Mitochondrial DNA mutation* - Mitochondria are inherited exclusively from the mother, and mutations in **mitochondrial DNA** can cause a range of disorders affecting energy production. - While these disorders can vary in severity due to **heteroplasmy**, they do not typically show a pattern of increasing severity in successive generations due to an expanding repeat sequence.

Q: Which one of the following enzymes is obtained from Thermus aquaticus bacterium that is heat stable and used in PCR at high temperature?

Taq polymerase. ***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.

Q: Transgenic animals are:

All of the options. ***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."

Q: DNA polymerase used in PCR is derived from which organism?

Thermus aquaticus. ***Thermus aquaticus*** - The **DNA polymerase** used in PCR is typically isolated from the bacterium **Thermus aquaticus**, known as **Taq polymerase**. - This enzyme is chosen because of its **thermostability**, meaning it can withstand the high temperatures required to denature DNA during each PCR cycle without degrading. *Bacteriophages* - **Bacteriophages** are viruses that infect bacteria, and while some encode their own **DNA polymerases**, these are generally not thermostable enough for PCR. - Phage-derived polymerases are used in other molecular biology techniques but not typically in standard PCR due to thermal instability. *E. coli* - **E. coli** produces **DNA polymerase I**, which is essential for DNA replication and repair in the cell but is **not thermostable**. - Its polymerase would denature at the high temperatures used in the PCR denaturation step, rendering it unsuitable for the reaction. *Retroviruses* - **Retroviruses** primarily encode **reverse transcriptase**, which is an RNA-dependent DNA polymerase. - This enzyme synthesizes DNA from an RNA template and is not suitable for the DNA-dependent DNA synthesis required in standard PCR.

Q: Recombinant human insulin is made by -

cDNA of pancreatic cell. ***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.

Q: DNA fingerprinting was discovered by:

Jeffreys. ***Jeffreys*** - **Alec Jeffreys** developed the technique of **DNA fingerprinting** (also known as DNA profiling) in 1984. - This method utilizes the repetitive sequences of **DNA** (minisatellites) to create a unique genetic profile for individuals. *Galton* - **Francis Galton** was a pioneer in **eugenics** and developed the concept of **fingerprint classification** for identification, but not DNA fingerprinting. - His work was primarily focused on human heredity and **statistics** in the late 19th century. *Crick* - **Francis Crick**, along with James Watson, discovered the **double helix structure of DNA**. - His contributions were fundamental to understanding genetics but he did not discover DNA fingerprinting. *Southern* - **Edwin Southern** developed the **Southern blot technique**, which is used to detect specific **DNA sequences** in a sample. - While related to DNA analysis, the Southern blot is a method for detecting sequences, not the overall concept of DNA fingerprinting for identification.

Question 1

Retrovirus is used for gene therapy because -

Accepted Answer

They integrate stably into human genome

Answer

They have sequences common to human genome

Answer

Easy to perform in labs

Answer

Economically viable

Question 2

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

Accepted Answer

λ

Answer

β

Answer

α

Answer

None of the options

Question 3

True about polymerase chain reaction is:

Accepted Answer

Enzymatic DNA amplification

Answer

Non-enzymatic DNA amplification

Answer

Recombinant DNA amplification

Answer

Separation of protein fragments in serum

Question 4

Increasing severity of intellectual disability of male members over generations is a result of ?

Accepted Answer

Trinucleotide repeat mutation

Answer

Y linked disorder

Answer

Frameshift mutation

Answer

Mitochondrial DNA mutation

Question 5

Which one of the following enzymes is obtained from Thermus aquaticus bacterium that is heat stable and used in PCR at high temperature?

Accepted Answer

Taq polymerase

Answer

DNA gyrase

Answer

DNA polymerase III

Answer

Endonuclease

Question 6

Transgenic animals are:

Accepted Answer

All of the options

Answer

Genetically modified organisms with a new heritable character

Answer

Serve as models for understanding human diseases

Answer

Proteins produced by them are used as therapeutic agents

Question 7

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

Accepted Answer

DNA can be isolated from blood, skin, or sperm and analyzed for variable patterns of restriction fragments arising from tandemly repeated sequences (microsatellites)

Answer

DNA is isolated from blood, skin, or sperm and its fragment size distribution is analyzed by gel electrophoresis

Answer

DNA is isolated from blood, skin, or sperm and hybridized with probes from the HLA locus to visualize HLA gene patterns

Answer

DNA is copied from blood, skin, or sperm RNA using reverse transcriptase and analyzed for the pattern of complementary DNAs

Question 8

DNA polymerase used in PCR is derived from which organism?

Accepted Answer

Thermus aquaticus

Answer

Bacteriophages

Answer

E. coli

Answer

Retroviruses

Question 9

Recombinant human insulin is made by -

Accepted Answer

cDNA of pancreatic cell

Answer

cDNA from any eukaryote cell

Answer

Genome of pancreatic cell

Answer

Genome of any eukaryote

Question 10

DNA fingerprinting was discovered by:

Accepted Answer

Jeffreys

Answer

Galton

Answer

Crick

Answer

Southern

Molecular Biology and Genomics — MCQs

Molecular Biology and Genomics — MCQs

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