Molecular Biology and Genomics Practice Questions

Q: Which biomedical tool used in DNA technology utilizes an oligomer with a single base pair substitution?

Restriction Fragment Length Polymorphism (RFLP). ### Explanation **Correct Option: B. Restriction Fragment Length Polymorphism (RFLP)** RFLP is a technique used to detect variations in DNA sequences. The underlying principle relies on the fact that a **single base pair substitution** (a Single Nucleotide Polymorphism or SNP) can either create or abolish a specific recognition site for a **restriction endonuclease**. When the DNA is digested with these enzymes, the resulting fragments differ in length between individuals. These fragments are then separated by electrophoresis and hybridized with a labeled **oligomer (DNA probe)** to visualize the specific polymorphic regions. This tool is classic for linkage analysis and identifying genetic disease carriers (e.g., Sickle Cell Anemia). **Analysis of Incorrect Options:** * **A. PCR:** This is an amplification technique using primers to exponentially increase DNA quantity. While it can be used *prior* to RFLP, the PCR process itself does not inherently rely on single base substitutions to function. * **C. Error coded mutation analysis:** This is a distractor term. While "Allele-Specific Oligonucleotide (ASO)" probes detect mutations, they are not the standard definition for the process described in the context of traditional RFLP. * **D. FISH:** This technique uses fluorescent probes to detect the presence, absence, or location of specific **large DNA sequences** or whole genes on chromosomes. It is used for gross chromosomal abnormalities (e.g., Trisomy 21, BCR-ABL translocation) rather than single base substitutions. **Clinical Pearls for NEET-PG:** * **Sickle Cell Anemia:** The classic RFLP example where a mutation in the $\beta$-globin gene destroys the *MstII* restriction site. * **VNTRs:** Variable Number Tandem Repeats are the basis for DNA fingerprinting, often analyzed via RFLP. * **Southern Blotting:** The laboratory technique required to visualize RFLP fragments.

Q: Which of the following methods is most suited to assess the function of a gene?

Gene knockout animals. To assess the **function** of a gene, we must observe the physiological consequences when that gene is absent. This is the principle of "Reverse Genetics." ### Why "Gene Knockout Animals" is Correct A **Gene Knockout** involves the deliberate inactivation or "deletion" of a specific gene within an organism’s genome. By comparing the phenotype of the knockout animal with a wild-type (normal) animal, researchers can determine exactly what biological processes that gene controls. For example, knocking out the *LDL receptor* gene in mice leads to hypercholesterolemia, confirming its function in cholesterol clearance. ### Why Other Options are Incorrect * **Southern Blot:** Used for the detection of a specific **DNA sequence** in a sample. It identifies the presence or size of a gene but does not provide information about its biological function. * **Northern Blot:** Used to study **gene expression** by detecting specific **RNA** molecules. While it shows if a gene is "active," it doesn't prove what the resulting protein actually does in the body. * **Transgenic Animals:** These animals have a **foreign gene inserted** into their genome (Gain-of-function). While useful, adding a gene can sometimes cause non-specific effects or overexpression artifacts, making "Knockout" (Loss-of-function) the gold standard for defining a gene's essential baseline function. ### High-Yield NEET-PG Pearls * **SNOW DROP Mnemonic:** **S**outhern-**D**NA, **N**orthern-**R**NA, **O**-**O**, **W**estern-**P**rotein. * **Knock-in:** A variation where a mutated gene is substituted for the normal gene to study specific diseases (e.g., Sickle Cell models). * **RNA Interference (RNAi):** Another method to study function by "silencing" mRNA, often called a "Gene Knockdown." * **CRISPR-Cas9:** The most modern and efficient tool used to create knockout models.

Q: Polypeptide chain termination is enhanced by:

Stop codon. ### Explanation **Why the Correct Answer is Right:** Translation termination occurs when the ribosome encounters one of the three **stop codons** (UAA, UAG, or UGA) on the mRNA. Unlike other codons, stop codons do not code for an amino acid and are not recognized by tRNA. Instead, they are recognized by **Release Factors (RFs)**. These factors trigger the peptidyl transferase to catalyze the addition of a water molecule instead of an amino acid, leading to the hydrolysis of the bond between the completed polypeptide chain and the tRNA, thereby releasing the protein. **Analysis of Incorrect Options:** * **B. Promoter:** This is a DNA sequence located upstream of a gene where RNA polymerase binds to initiate **transcription**, not translation. It has no role in polypeptide chain termination. * **C. Ribosomal unit:** While the ribosome is the machinery where translation occurs, the units themselves (40S/60S in eukaryotes) do not "enhance" termination; they dissociate *after* the stop codon is recognized by release factors. * **D. All:** Incorrect, as only the stop codon serves as the specific signal for termination. **NEET-PG High-Yield Pearls:** * **Mnemonic for Stop Codons:** **U** **A**re **A**way (UAA), **U** **A**re **G**one (UAG), **U** **G**o **A**way (UGA). * **Release Factors:** In Prokaryotes, RF1 (UAA, UAG) and RF2 (UAA, UGA) are used. In Eukaryotes, a single factor, **eRF1**, recognizes all three stop codons. * **Nonsense Mutation:** A point mutation that results in a premature stop codon, leading to a truncated, usually non-functional protein (e.g., in some forms of Beta-thalassemia). * **Energy Requirement:** Termination is an energy-dependent process requiring **GTP** hydrolysis.

Q: Genomic imprinting is seen in which of the following conditions?

Prader-Willi syndrome. **Explanation:** **Genomic Imprinting** is an epigenetic phenomenon where certain genes are expressed in a parent-of-origin-specific manner. While most autosomal genes are expressed from both alleles, imprinted genes are "silenced" (via DNA methylation) on either the maternal or paternal chromosome. **Why Prader-Willi Syndrome (PWS) is correct:** PWS is a classic example of genomic imprinting involving chromosome **15q11-q13**. In normal individuals, the PWS gene is active on the paternal chromosome and silenced (imprinted) on the maternal one. PWS occurs when the **paternal** contribution is lost—either through microdeletion (70%), Maternal Uniparental Disomy (25%), or imprinting defects. Conversely, loss of the **maternal** contribution in the same region leads to **Angelman Syndrome**. **Why the other options are incorrect:** * **Marfan Syndrome:** An autosomal dominant disorder caused by mutations in the *FBN1* gene (Fibrillin-1). It follows Mendelian inheritance, not imprinting. * **Ehlers-Danlos Syndrome:** A heterogeneous group of connective tissue disorders (mostly autosomal dominant or recessive) involving collagen synthesis defects. * **Osteogenesis Imperfecta:** Primarily an autosomal dominant "brittle bone" disease caused by mutations in *COL1A1* or *COL1A2* genes. **High-Yield Clinical Pearls for NEET-PG:** * **PWS Mnemonic:** **P**aternal **D**eletion = **P**rader-Willi (presents with hyperphagia, obesity, hypogonadism, and hypotonia). * **Angelman Mnemonic:** **M**aternal **D**eletion = **A**ngelman (presents with inappropriate laughter/“Happy Puppet,” seizures, and ataxia). * **Other Imprinting Disorders:** Beckwith-Wiedemann Syndrome (Chromosome 11p15) and Silver-Russell Syndrome. * **Mechanism:** Imprinting occurs during **gametogenesis** and is maintained throughout mitosis in somatic cells.

Q: Which of the following is NOT a feature of the genetic code?

Ambiguous. The genetic code is a set of rules used by living cells to translate information encoded within genetic material into proteins. Understanding its properties is fundamental for medical biochemistry. ### **Why "Ambiguous" is the Correct Answer** The genetic code is **unambiguous**, not ambiguous. This means that **one specific codon always codes for one specific amino acid**. For example, the codon UUU always codes for Phenylalanine and nothing else. If the code were "ambiguous," a single codon could code for multiple different amino acids, which would lead to the synthesis of unpredictable and non-functional proteins. ### **Explanation of Incorrect Options** * **B. Non-overlapping:** The code is read sequentially, three bases at a time. A single base is part of only one codon and is not shared between adjacent codons. * **C. Commaless:** There are no "punctuation marks" or spacers between codons. Once translation begins at the start codon (AUG), the mRNA is read continuously until a stop codon is reached. * **D. Specific:** This is a synonym for "unambiguous." It reinforces that a particular codon is dedicated to a specific amino acid. ### **High-Yield Clinical Pearls for NEET-PG** * **Degeneracy (Redundancy):** While one codon codes for only one amino acid (unambiguous), **one amino acid can be coded by multiple codons** (e.g., Leucine has six codons). This provides protection against silent mutations. * **Universality:** The code is the same in almost all organisms. **Exception:** Mitochondrial DNA (e.g., UGA codes for Tryptophan in mitochondria, but is a Stop codon in the cytosol). * **Wobble Hypothesis:** Proposed by Francis Crick; it explains why the third base of a codon can sometimes vary without changing the amino acid, allowing one tRNA to recognize multiple codons.

Q: What is true about the coding strand of DNA?

Runs in the 5'-3' direction. **Explanation:** In molecular biology, DNA transcription involves two strands with distinct roles. The **coding strand** (also known as the **sense strand** or **plus (+) strand**) is the DNA strand whose base sequence corresponds directly to the sequence of the RNA transcript produced (with Thymine replaced by Uracil). **Why Option D is Correct:** By convention, the coding strand is always written in the **5' to 3' direction**. This matches the direction of the newly synthesized mRNA and the direction in which the ribosome reads the genetic code during translation. Because it "codes" for the protein sequence in the same orientation as the mRNA, it is designated as the 5'-3' strand. **Analysis of Incorrect Options:** * **Option A (Minus strand):** The coding strand is the **plus (+)** strand. The "minus" (-) strand refers to the template strand. * **Option B (Template strand):** The template strand (or antisense strand) is the one actually read by RNA polymerase to synthesize RNA via complementary base pairing. The coding strand is the non-template strand. * **Option C (Runs in the 3'-5' direction):** This describes the **template strand**. RNA polymerase moves along the template strand in a 3' to 5' direction so that it can synthesize the new RNA molecule in a 5' to 3' direction. **High-Yield Clinical Pearls for NEET-PG:** * **Directionality:** DNA synthesis (Replication), RNA synthesis (Transcription), and Protein synthesis (Translation) all occur in the **5' → 3' direction**. * **Sequence Identity:** The mRNA sequence is identical to the **coding strand** (except U for T) and complementary to the **template strand**. * **Promoters:** Regulatory sequences like the TATA box are described based on their position on the **coding strand**.

Q: What are the main components of a chromosome?

DNA. ### Explanation **1. Why DNA is the Correct Answer:** Chromosomes are the organized structures of genetic material found in the nucleus of eukaryotic cells. The primary chemical component of a chromosome is **Deoxyribonucleic Acid (DNA)**, which carries the hereditary information. In humans, DNA is tightly coiled around basic proteins called **histones** to form nucleosomes (the "beads on a string" structure), which further condense into chromatin and eventually chromosomes during cell division. **2. Why the Other Options are Incorrect:** * **tRNA (Transfer RNA):** These are small RNA molecules (70-90 nucleotides) found in the **cytosol**. Their role is to transport specific amino acids to the ribosome during translation; they are not structural components of chromosomes. * **mRNA (Messenger RNA):** This is a transient molecule synthesized in the nucleus (via transcription) that carries genetic code to the cytoplasm for protein synthesis. It does not form the structural framework of a chromosome. * **rRNA (Ribosomal RNA):** This is the catalytic component of **ribosomes**. While synthesized in the nucleolus, it functions in the cytoplasm to facilitate protein synthesis. **3. NEET-PG High-Yield Clinical Pearls:** * **Nucleosome Core:** Consists of an octamer of histones (**H2A, H2B, H3, and H4**) with 146 base pairs of DNA wrapped around it. **Histone H1** acts as the "linker" protein. * **Euchromatin vs. Heterochromatin:** Euchromatin is transcriptionally active (loose), while heterochromatin is inactive (dense). * **Clinical Correlation:** Drugs like **Valproic acid** act as Histone Deacetylase (HDAC) inhibitors, altering chromosome condensation to affect gene expression. * **Karyotyping:** Chromosomes are best visualized during the **Metaphase** stage of mitosis using Colchicine to arrest the cell cycle.

Q: What is an Okazaki fragment?

Synthesized by DNA polymerase delta in eukaryotes. **Explanation:** DNA replication is **semi-discontinuous**. While the leading strand is synthesized continuously, the **lagging strand** is synthesized in short, discontinuous segments known as **Okazaki fragments**. **Why Option B is correct:** In eukaryotes, DNA replication involves specific polymerases. While **Pol α** (alpha) initiates synthesis with an RNA primer, **DNA Polymerase δ (delta)** is the primary enzyme responsible for the elongation of the lagging strand (Okazaki fragments). It possesses high processivity and 3'→5' exonuclease activity for proofreading. **Analysis of Incorrect Options:** * **Option A:** Okazaki fragments are synthesized exclusively along the **lagging strand** (3' to 5' template direction) because DNA polymerase can only synthesize DNA in the 5' to 3' direction. * **Option C:** While Flap endonuclease I (FEN1) removes the RNA primers in eukaryotes, the actual "joining" or sealing of the nicks between fragments is performed by **DNA Ligase I**. * **Option D:** In prokaryotes (like *E. coli*), Okazaki fragments are synthesized by **DNA Polymerase III**. DNA Polymerase I is responsible for removing the RNA primer and filling the resulting gaps. **High-Yield Clinical Pearls for NEET-PG:** * **Polymerase Switching:** The transition from Pol α to Pol δ/ε is called polymerase switching. * **Eukaryotic Polymerases:** Remember **"α, δ, ε"**: * **α (Alpha):** Primase activity (starts the chain). * **δ (Delta):** Lagging strand synthesis. * **ε (Epsilon):** Leading strand synthesis. * **γ (Gamma):** Mitochondrial DNA replication. * **DNA Ligase:** Uses ATP in eukaryotes but NAD+ in some bacteria to form the phosphodiester bond.

Q: Restriction fragment length polymorphism is used for?

Analysis of chromosome structures. **Explanation:** **Restriction Fragment Length Polymorphism (RFLP)** is a molecular technique used to detect variations in homologous DNA sequences. It relies on the use of **Restriction Endonucleases**, which act as "molecular scissors" to cut DNA at specific recognition sites. 1. **Why Option A is Correct:** RFLP is used for the **analysis of chromosome structures** because mutations (substitutions, insertions, or deletions) within a DNA sequence can create or abolish recognition sites for restriction enzymes. This results in DNA fragments of varying lengths. By comparing these fragment patterns, scientists can map genes, identify chromosomal rearrangements, and detect genetic polymorphisms associated with specific diseases (e.g., Sickle Cell Anemia). 2. **Why Other Options are Incorrect:** * **B. DNA estimation:** This is typically done using **Spectrophotometry** (measuring absorbance at 260 nm) or fluorometry, not RFLP. * **C. Synthesis of nucleic acid:** This refers to processes like **PCR (Polymerase Chain Reaction)** or automated DNA synthesis, whereas RFLP is an analytical/diagnostic tool. * **D. Detecting proteins:** Protein detection is achieved through **Western Blotting** or ELISA. RFLP is strictly a DNA-based technique. **High-Yield Clinical Pearls for NEET-PG:** * **Southern Blotting:** RFLP analysis is traditionally performed using the Southern Blot technique. * **Sickle Cell Anemia:** A classic application of RFLP is detecting the loss of the *MstII* restriction site in the β-globin gene. * **DNA Fingerprinting:** RFLP was the original method used for forensic DNA profiling and paternity testing (though now largely replaced by STR analysis). * **Mapping:** It is a primary tool for **Linkage Analysis** to locate disease-causing genes on specific chromosomes.

Question 1

Which biomedical tool used in DNA technology utilizes an oligomer with a single base pair substitution?

Accepted Answer

Restriction Fragment Length Polymorphism (RFLP)

Answer

Polymerase Chain Reaction (PCR)

Answer

Error coded mutation analysis

Answer

Fluorescence In Situ Hybridization (FISH)

Question 2

Which of the following methods is most suited to assess the function of a gene?

Accepted Answer

Gene knockout animals

Answer

Southern blot

Answer

Northern blot

Answer

Transgenic animals

Question 3

Polypeptide chain termination is enhanced by:

Accepted Answer

Stop codon

Answer

Promoter

Answer

Ribosomal unit

Answer

All

Question 4

A mutation that converts an amino acid codon to a stop codon is a:

Accepted Answer

Nonsense mutation

Answer

Transversion

Answer

Silent mutation

Answer

Frame shift mutation

Question 5

Genomic imprinting is seen in which of the following conditions?

Accepted Answer

Prader-Willi syndrome

Answer

Marfan syndrome

Answer

Ehlers-Danlos syndrome

Answer

Osteogenesis imperfecta

Question 6

Which of the following is NOT a feature of the genetic code?

Accepted Answer

Ambiguous

Answer

Non-overlapping

Answer

Commaless

Answer

Specific

Question 7

What is true about the coding strand of DNA?

Accepted Answer

Runs in the 5'-3' direction

Answer

Minus strand

Answer

Template strand

Answer

Runs in the 3'-5' direction

Question 8

What are the main components of a chromosome?

Accepted Answer

DNA

Answer

Transfer RNA (tRNA)

Answer

Messenger RNA (mRNA)

Answer

Ribosomal RNA (rRNA)

Question 9

What is an Okazaki fragment?

Accepted Answer

Synthesized by DNA polymerase delta in eukaryotes

Answer

Synthesized along the leading strand

Answer

Joined by Flap endonuclease I

Answer

Synthesized by DNA polymerase I in prokaryotes

Question 10

Restriction fragment length polymorphism is used for?

Accepted Answer

Analysis of chromosome structures

Answer

DNA estimation

Answer

Synthesis of nucleic acid

Answer

Detecting proteins in a cell

Molecular Biology and Genomics — MCQs

Molecular Biology and Genomics — MCQs

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