Biochemical Techniques — MCQs

Biochemical Techniques Indian Medical PG Practice Questions and MCQs

Question 211: Which of the following enzymes is used in Recombinant DNA research for Homopolymer tailing?

A. S1 nuclease
B. Polynucleotide kinase
C. Terminal transferase (Correct Answer)
D. Reverse transcriptase

Explanation: ***Terminal transferase*** - **Terminal transferase** is an enzyme that adds **deoxyribonucleotides** to the 3'-hydroxyl terminus of a DNA strand **independently of a template**. - This capability makes it ideal for **homopolymer tailing**, where a series of identical nucleotides (e.g., poly-A or poly-T tails) are added to the ends of DNA molecules to facilitate cloning. *S1 nuclease* - **S1 nuclease** is a single-strand specific **endonuclease** that degrades single-stranded DNA or RNA. - Its primary use is in removing **single-stranded overhangs** or converting **sticky ends to blunt ends**, not in adding nucleotide tails. *Polynucleotide kinase* - **Polynucleotide kinase** catalyzes the transfer of the **gamma-phosphate from ATP to the 5'-hydroxyl terminus** of DNA or RNA. - It is used for **labeling DNA/RNA fragments** or for phosphorylation prior to ligation, not for adding long homopolymer tails. *Reverse transcriptase* - **Reverse transcriptase** is a **DNA polymerase** that synthesizes a DNA strand from an RNA template (reverse transcription). - Its main roles are in **cDNA synthesis** from mRNA and in the study of retroviruses, not in adding homopolymer tails to DNA.

Question 212: Northern Blot is used to detect

A. DNA
B. Proteins
C. Enzymes
D. RNA (Correct Answer)

Explanation: ***RNA*** - Northern blot analysis is a laboratory technique used to detect specific **RNA sequences** in a sample. - This method involves **electrophoresis** to separate RNA fragments by size, followed by transfer to a membrane and hybridization with a labeled RNA or DNA probe. *DNA* - **Southern blotting** is the technique specifically designed for detecting **DNA sequences**. - It involves digesting DNA with restriction enzymes, separating fragments by electrophoresis, and hybridizing with a labeled DNA probe. *Proteins* - **Western blotting** is the technique used for detecting and analyzing **proteins**. - Proteins are separated by size using SDS-PAGE, transferred to a membrane, and then probed with specific antibodies. *Enzymes* - While enzymes are proteins, directly detecting **enzyme activity** or specific enzymes often involves **activity assays** or **immunological methods** like ELISA, rather than Northern blotting. - Northern blotting identifies mRNA transcripts, which are templates for protein (including enzyme) synthesis, but not the enzymes themselves.

Question 213: Which of the following is NOT true about hybridoma?

A. DNA sequencing
B. In-situ hybridization (Correct Answer)
C. Formation of continuous cell line
D. Formation of monoclonal antibodies

Explanation: ***In-situ hybridization*** - Hybridoma technology is used to produce **monoclonal antibodies**, not for **in-situ hybridization**, which is a molecular biology technique for detecting specific nucleic acid sequences within cells or tissues. - While antibodies produced by hybridomas can be used in immunohistochemistry (a related technique), the hybridoma process itself does not involve **in-situ hybridization**. *DNA sequencing* - **DNA sequencing** is a technique to determine the order of nucleotide bases in a DNA molecule. - Hybridoma technology is focused on producing antibodies from fused cells, not on directly sequencing DNA, though antibodies could be used in research to study DNA-binding proteins. *Formation of continuous cell line* - One of the primary advantages of hybridoma technology is the creation of a **continuous cell line** by fusing antibody-producing B cells with myeloma cells. - This immortalized cell line allows for the consistent and long-term production of specific antibodies. *Formation of monoclonal antibodies* - The main purpose of the hybridoma technique is the production of **monoclonal antibodies**, which are highly specific antibodies that recognize a single epitope. - These antibodies have broad applications in diagnostics, therapeutics, and research.

Question 214: The fastest moving amino acid in methanol-chloroform electrophoresis is:

A. Glycine (Correct Answer)
B. Valine
C. Leucine
D. Aspartic Acid

Explanation: ***Glycine*** - In **methanol-chloroform electrophoresis** (a **non-polar solvent system**), amino acids exist primarily in their **non-ionized forms**, unlike aqueous electrophoresis. - Migration depends on **molecular size and polarity** rather than ionic charge. - **Glycine** is the **smallest amino acid** (molecular weight 75 Da) with minimal side chain interactions, allowing it to move fastest through the non-polar medium. - Its simple structure (H as side chain) provides the least resistance to movement in organic solvents. *Aspartic Acid* - **Aspartic acid** is an acidic amino acid that would be in its **non-ionized form** in the non-polar methanol-chloroform system. - Its **larger size** and **polar carboxyl groups** create more interactions with the solvent, slowing its migration. - The concept of "net negative charge" does not apply in non-polar solvents where ionization is minimal. *Valine* - **Valine** is a **branched-chain, hydrophobic amino acid** with a larger side chain than glycine. - While it is non-polar and compatible with the solvent, its **larger molecular size** (117 Da) results in slower migration compared to glycine. *Leucine* - **Leucine** is also a **branched-chain, hydrophobic amino acid** with an even larger side chain than valine (131 Da). - Its **larger molecular size** and bulkier structure create more resistance to movement through the electrophoretic medium, making it the slowest among the options.

Question 215: Column chromatography using phenyl Sepharose beads separates proteins based on the

A. Hydrophobicity (Correct Answer)
B. Charge
C. Stokes' radius
D. Affinity to ligand

Explanation: ***Hydrophobicity*** - Phenyl Sepharose beads are designed with **hydrophobic phenyl groups** covalently linked to the Sepharose matrix. - Proteins with higher inherent hydrophobicity interact more strongly with these phenyl groups, leading to **retention on the column** and separation based on their **hydrophobic tendencies**. *Charge* - Separation based on charge typically employs **ion-exchange chromatography**, which uses charged resins to bind proteins based on their overall net charge. - Phenyl Sepharose chromatography does **not primarily separate** proteins based on their electrostatic properties. *Stokes' radius* - Separation based on Stokes' radius (or molecular size) is achieved using **size-exclusion chromatography** (or gel filtration chromatography), where porous beads fractionate proteins based on their ability to enter the pores. - Phenyl Sepharose chromatography does **not primarily rely on size exclusion** for protein separation. *Affinity to ligand* - Separation based on affinity to a specific ligand is characteristic of **affinity chromatography**, where a ligand is immobilized on the matrix to specifically bind a target protein. - While phenyl groups can be considered ligands, their interaction is general hydrophobic, not specific to a particular protein-ligand binding site.

Question 216: In estimation of bilirubin, the solution is examined at

A. 540 nm
B. 450 nm (Correct Answer)
C. 480 nm
D. 580 nm

Explanation: ***450 nm*** - **Bilirubin** absorbs light most strongly at a wavelength of approximately **450 nm**, which is in the **blue-violet region** of the visible spectrum. - This wavelength is used in the **Jendrassik-Gróf method** and other **spectrophotometric methods** for accurate estimation of bilirubin concentration. *540 nm* - This wavelength is typically used in assays for metabolites such as **glucose** and **uric acid**, often after a colorimetric reaction. - It is not the optimal absorption maximum for bilirubin and would lead to less accurate readings. *480 nm* - While close to the bilirubin absorption peak, **480 nm** is not the maximal absorption wavelength and would result in reduced sensitivity and accuracy. - Using a wavelength slightly off the maximum peak means that not all of the light absorbed will be due to bilirubin, introducing error. *580 nm* - This wavelength is too far from the peak absorption of bilirubin, which is in the blue-violet region. - Using **580 nm** would result in very little light absorption by **bilirubin**, making it unsuitable for quantitative analysis.

Question 217: A chemical is tested for carcinogenicity by examining its mutagenic effects on bacterial cells in culture. Which of the following tests is used to make this determination?

A. Ames test (Correct Answer)
B. Watson-Schwartz test
C. Widal test
D. Nitroblue tetrazolium test

Explanation: ***Ames test*** - The **Ames test** is a widely used biological assay to assess the **mutagenic potential** of chemical compounds. - It uses specific strains of bacteria (e.g., *Salmonella typhimurium* or *Escherichia coli*) that have been genetically modified to require a particular nutrient (e.g., histidine) for growth and examines the frequency of **reverse mutations** that allow them to grow without that nutrient, indicating mutagenicity. *Watson-Schwartz test* - The **Watson-Schwartz test** is a biochemical test used to detect the presence of **porphobilinogen** in urine, primarily for diagnosing acute intermittent porphyria. - It is not related to assessing mutagenicity or carcinogenicity. *Widal test* - The **Widal test** is a serological test used for the diagnosis of **typhoid fever** by detecting antibodies against *Salmonella typhi* O and H antigens in a patient's serum. - It is an immunological test and does not assess mutagenic effects. *Nitroblue tetrazolium test* - The **Nitroblue tetrazolium (NBT) test** is used to assess the phagocytic function of **neutrophils**, primarily to diagnose **chronic granulomatous disease (CGD)**. - It measures the ability of neutrophils to produce **superoxide radicals** and is not related to carcinogenicity or mutagenicity.

Question 218: Ammonium oxalate reagent is commonly used in analytical chemistry for the detection of:

A. Ammonium molybdate
B. Sodium phosphomolybdate
C. Calcium (Correct Answer)
D. Magnesium

Explanation: ***Calcium*** - Ammonium oxalate is the **standard reagent** used for the qualitative and quantitative detection of **calcium ions** (Ca²⁺) in analytical chemistry. - It forms a **white crystalline precipitate** of calcium oxalate (CaC₂O₄·H₂O) which is insoluble in water and acetic acid. - This is a **classical precipitation reaction** widely used in clinical laboratories for calcium estimation and in urine analysis for detecting calcium oxalate crystals. - The reaction is: Ca²⁺ + (NH₄)₂C₂O₄ → CaC₂O₄↓ + 2NH₄⁺ *Ammonium molybdate* - This compound is itself a *reagent* used for detecting **phosphate ions**, not a substance detected by ammonium oxalate. - It forms yellow ammonium phosphomolybdate complex in the presence of phosphates under acidic conditions. *Sodium phosphomolybdate* - This is a *product formed* in phosphate detection tests using ammonium molybdate. - It is not detected by ammonium oxalate, which is specific for calcium ion detection. *Magnesium* - Magnesium ions are detected using a *different reagent system* - typically disodium hydrogen phosphate (Na₂HPO₄) in the presence of ammonium hydroxide. - This forms magnesium ammonium phosphate (struvite) precipitate, **not** a reaction with ammonium oxalate. - Ammonium oxalate does not form a characteristic precipitate with magnesium ions.

Question 219: Radioactive nuclides used in medical imaging that have the same atomic number but different mass numbers are termed:

A. Isobars
B. Isomers
C. Isotopes (Correct Answer)
D. Isotones

Explanation: ***Isotopes*** - Isotopes are atoms of the same element (same **atomic number** or number of protons) but with different mass numbers (different number of neutrons). - This property allows them to be chemically identical but have different nuclear properties, making them useful in **medical imaging** (e.g., technetium-99m). *Isobars* - Isobars are atoms with the same **mass number** but different atomic numbers (different elements). - They have different chemical properties and are not the primary basis for radioactive nuclides in medical imaging in this context. *Isomers* - Isomers are nuclides with the same atomic and mass numbers but in different **nuclear energy states**. - **Technetium-99m** is a metastable isomer widely used in nuclear medicine, but the definition in the question refers to variations in mass number for a given atomic number. *Isotones* - Isotones are atoms with the same number of **neutrons** but different numbers of protons (different elements). - Like isobars, they represent different elements and are not defined by having the same atomic number but different mass numbers.

Question 220: Separation of proteins based on size is done by

A. Affinity chromatography
B. High performance liquid chromatography
C. SDS-Polyacrylamide gel electrophoresis (Correct Answer)
D. Ion exchange chromatography

Explanation: ***SDS-Polyacrylamide gel electrophoresis*** - **SDS-PAGE** separates proteins primarily based on their **molecular weight** (size). - Proteins are denatured and coated with negatively charged **SDS**, causing them to migrate through a polyacrylamide gel based on size. *Affinity chromatography* - This technique separates proteins based on their **specific binding affinity** to a ligand. - It does not directly separate based on size, but rather on **molecular recognition**. *High performance liquid chromatography* - **HPLC** is a chromatographic technique that separates molecules in a complex mixture, but the primary basis of separation depends on the column type. - While some HPLC methods (**size-exclusion HPLC**) can separate by size, it is a broader technique and not the most specific answer for protein size separation in general context. *Ion exchange chromatography* - This method separates proteins based on their **net charge** at a particular pH. - Proteins bind to a charged resin and are eluted by increasing salt concentration or changing pH, not based on size.

Practice by Chapter

Spectrophotometry and Colorimetry

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Chromatography Techniques

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Electrophoresis and Applications

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Centrifugation and Ultracentrifugation

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Radioisotope Techniques

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Enzyme-Linked Immunosorbent Assay (ELISA)

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Polymerase Chain Reaction (PCR)

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Blotting Techniques: Southern, Northern, Western

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Mass Spectrometry in Biochemistry

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Recombinant DNA Technology

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DNA Sequencing

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Proteomics and Metabolomics

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