Biochemical Techniques — MCQs

Biochemical Techniques Indian Medical PG Practice Questions and MCQs

Question 221: Which technique is used for protein separation based on molecular size?

A. Affinity chromatography
B. Gel filtration chromatography (Correct Answer)
C. HPLC
D. Salting out

Explanation: ***Gel filtration chromatography*** - Also known as **size-exclusion chromatography**, this method separates proteins by passing them through a porous matrix. **Larger proteins** elute first as they cannot enter the pores, while smaller proteins get trapped and elute later. - This technique effectively separates proteins based solely on their **hydrodynamic radius**, which is closely related to their molecular size. *Affinity chromatography* - This method separates proteins based on their **specific binding affinity** to a ligand immobilized on a stationary phase, not molecular size. - It is used for purifying proteins that bind to a specific molecule, such as an antibody or substrate. *HPLC* - **High-performance liquid chromatography** is a general technique that can use various separation mechanisms (e.g., reverse-phase, ion-exchange, size-exclusion) under high pressure. - While it *can* be used for size-exclusion, HPLC itself describes the *method* of chromatographic performance rather than a specific separation principle based on molecular size alone. *Salting out* - This technique separates proteins based on their **solubility** in high salt concentrations. - As salt concentration increases, the proteins lose their hydration shells and precipitate out of solution, with different proteins precipitating at different salt concentrations.

Question 222: Which among the following is identified by Western blotting

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

Explanation: ***Proteins*** - **Western blotting** is a widely used analytical technique in molecular biology and immunogenetics to detect specific **proteins** in a sample. - The technique involves separating proteins by gel electrophoresis, transferring them to a membrane, and then detecting the target protein using specific antibodies. *t-RNA* - **t-RNA** (transfer ribonucleic acid) is involved in protein synthesis but is not typically detected using Western blotting. - While other blotting techniques exist for RNA, Western blotting is specific for protein analysis, not for detecting different types of RNA. *RNA* - General **RNA** detection is usually performed using techniques like **Northern blotting** or RT-PCR, not Western blotting. - Western blotting relies on antibody-antigen interactions specific to protein structures. *DNA* - **DNA** is detected using techniques such as **Southern blotting** or PCR, not Western blotting. - Western blotting is designed to identify proteins based on their molecular weight and antigenicity.

Question 223: Gas commonly used for rapid induction of anesthesia

A. Nitrous oxide
B. Sevoflurane (Correct Answer)
C. Isoflurane
D. Desflurane

Explanation: ***Sevoflurane*** - Sevoflurane has a **low blood:gas partition coefficient**, leading to rapid equilibration between the lungs and blood, and thus rapid induction and emergence from anesthesia. - Its **non-pungent odor** and lack of airway irritation make it particularly suitable for children and adults requiring mask induction. *Nitrous oxide* - While it has a very low blood:gas partition coefficient, it is a **relatively weak anesthetic** and cannot achieve surgical depths of anesthesia on its own. - It is often used as an **adjunct** to other volatile anesthetics to reduce their required dose and speed up induction. *Isoflurane* - Isoflurane has a **higher blood:gas partition coefficient** compared to sevoflurane, resulting in a slower induction and emergence time. - Its **pungent odor** can cause coughing and airway irritation, making it less ideal for mask induction. *Desflurane* - Desflurane has the **lowest blood:gas partition coefficient** among the volatile anesthetics, leading to very rapid induction and emergence. - However, its **irritating effect on the airway** often causes coughing and laryngospasm, making it unsuitable for mask induction, especially in non-premedicated patients.

Question 224: Northern blotting used in separation and diagnosis of:

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

Explanation: ***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 225: Which of the following methods of protein separation is not dependent on molecular size?

A. Gel filtration chromatography
B. SDS-PAGE
C. Ultracentrifugation
D. Ion-exchange chromatography (Correct Answer)

Explanation: ***Ion-exchange chromatography*** - This method separates proteins based on their **net charge** at a specific pH. - Proteins bind to a charged resin based on their charge, independent of their size. *Gel filtration chromatography* - Separates proteins based on their **molecular size** and shape as they pass through a porous matrix. - **Larger molecules** elute first as they cannot enter the pores, while smaller molecules are retained. *SDS-PAGE* - **Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis** separates proteins primarily based on their **molecular weight**. - SDS denatures proteins and confers a uniform negative charge, allowing migration through a gel matrix based on size. *Ultracentrifugation* - Separates macromolecules and particles based on their **sedimentation rate**, which is influenced by **molecular mass**, density, and shape. - While molecular size is a factor, density and shape also play significant roles in the separation process.

Question 226: Which of the following defines isotopes?

A. Different atomic number and same mass number
B. Same atomic number and different mass number (Correct Answer)
C. Same atomic number and same mass number
D. Different atomic number and different mass number

Explanation: ***Same atomic number and different mass number*** - Isotopes are atoms of the same element, meaning they have the same number of **protons**, which defines the **atomic number**. - They differ in the number of **neutrons**, leading to a different **mass number** (protons + neutrons). *Different atomic number and same mass number* - This describes **isobars**, which are atoms of different elements but have the same total number of nucleons. - Having a different **atomic number** means they are different elements. *Same atomic number and same mass number* - This describes identical atoms of the **same element**, as both the number of protons and neutrons are the same. - These are simply different atoms of the same nuclide. *Different atomic number and different mass number* - This describes **different elements** with different numbers of protons and neutrons. - There is no specific term for this general category, as it just refers to distinct atomic species.

Question 227: All the following statements about hybridoma technology are true except:

A. HGPRT is required for the salvage pathway.
B. Aminopterin, a folate antagonist, inhibits de novo pathway.
C. Myeloma cells in salvage pathway grow well in HAT medium. (Correct Answer)
D. Specific antibody-producing cells are integrated with myeloma cells.

Explanation: ***Myeloma cells in salvage pathway grow well in HAT medium.*** - Myeloma cells used in hybridoma technology are typically deficient in **HGPRT (hypoxanthine-guanine phosphoribosyltransferase)**, which is essential for the **salvage pathway** of nucleotide synthesis. - Such HGPRT-deficient myeloma cells **cannot survive** in **HAT medium** because aminopterin blocks the de novo pathway, and without a functional salvage pathway, they cannot synthesize DNA. - This is the basis of **HAT selection** - only hybridoma cells (fused B cells + myeloma cells) survive because B cells provide functional HGPRT. *HGPRT is required for the salvage pathway.* - **HGPRT** (hypoxanthine-guanine phosphoribosyltransferase) is crucial for the **purine salvage pathway**, enabling cells to reuse hypoxanthine and guanine for nucleotide synthesis. - Cells with functional HGPRT can survive in HAT medium by using the salvage pathway when de novo synthesis is blocked. *Aminopterin, a folate antagonist, inhibits de novo pathway.* - **Aminopterin** is indeed a **folate antagonist** that inhibits **dihydrofolate reductase**, an enzyme critical for the *de novo* synthesis of purines and thymidylate. - By blocking this enzyme, aminopterin effectively **shuts down the *de novo* nucleotide synthesis pathway**, forcing cells to rely on the salvage pathway. *Specific antibody-producing cells are integrated with myeloma cells.* - In hybridoma technology, **antibody-producing B lymphocytes** (plasma cells) are fused with **myeloma cells** to create hybrid cells called hybridomas. - This fusion combines the antibody specificity and production capacity of B cells with the immortality and rapid division of myeloma cells, allowing for **continuous production** of monoclonal antibodies.

Question 228: Which amino acid migrates fastest on chromatography on carboxymethyl cellulose medium?

A. Glycine
B. Aspartic acid (Correct Answer)
C. Lysine
D. Valine

Explanation: ***Aspartic acid*** - Carboxymethyl cellulose (CMC) is a **cation exchange resin** with negatively charged carboxyl groups (-COO⁻). It binds positively charged molecules while **repelling negatively charged molecules**. - **Aspartic acid** is an **acidic amino acid** with a net negative charge at physiological pH, causing it to be **repelled** by the negatively charged resin and migrate **fastest**. - This electrostatic repulsion prevents binding and allows rapid elution. *Glycine* - **Glycine** is a **neutral amino acid** with minimal net charge at physiological pH. - It has weak or no electrostatic interaction with the resin, making it migrate at a moderate speed. - It lacks ionizable side chains, so its migration is slower than negatively charged amino acids but faster than positively charged ones. *Lysine* - **Lysine** is a **basic amino acid** and carries a net positive charge at physiological pH. - It **binds strongly** to the negatively charged CMC resin through electrostatic attraction. - This strong binding causes it to migrate **very slowly** or remain bound until eluted with high salt concentration. *Valine* - **Valine** is a **neutral, nonpolar amino acid** with no significant charge at physiological pH. - It has minimal electrostatic interaction with the CMC resin and migrates at a moderate speed. - It moves slower than negatively charged amino acids due to lack of electrostatic repulsion from the resin.

Question 229: Nephelometry measures the light?

A. Refracted
B. Transmitted
C. Scattered (Correct Answer)
D. Absorbed

Explanation: ***Scattered*** - **Nephelometry** measures the **light scattered** by particles in a liquid sample. - The intensity of the scattered light is directly proportional to the concentration of the analyte, such as immune complexes or proteins. *Refracted* - **Refraction** is the **bending of light** as it passes from one medium to another, like through a lens, and is not the principle behind nephelometry. - Refractive index measurements are used in techniques like refractometry, not nephelometry. *Transmitted* - **Transmitted light** is the light that passes directly through a sample without being absorbed or scattered. - Measuring transmitted light is the basis of **turbidimetry**, a related but distinct technique. *Absorbed* - **Absorbed light** is the light that is taken up by a substance, preventing it from passing through or being scattered. - Measuring absorbed light is the principle of **spectrophotometry** (e.g., colorimetry), not nephelometry.

Question 230: Pulsed gel electrophoresis is used for:

A. RNA
B. Protein
C. Ribosome
D. DNA (Correct Answer)

Explanation: ***DNA*** - **Pulsed-field gel electrophoresis (PFGE)** is a specialized technique used to separate **large DNA molecules** that are difficult to resolve using conventional gel electrophoresis. - It involves periodically changing the direction of the electric field, which forces large DNA molecules to reorient themselves, allowing for better separation based on size up to **10 Mb**. *RNA* - While conventional gel electrophoresis (e.g., agarose or polyacrylamide gels) can be used to separate **RNA molecules**, PFGE is not typically employed for RNA. - RNA molecules are generally much smaller than the large DNA fragments for which PFGE is designed, and their secondary structures can interfere with pulsed-field separation. *Protein* - **Proteins** are separated using different types of electrophoresis, such as **SDS-PAGE (sodium dodecyl sulfate-polyacrylamide gel electrophoresis)**, which separates proteins primarily by size. - PFGE is specifically designed for nucleic acids, particularly very large DNA, and is not suitable for protein separation. *Ribosome* - **Ribosomes** are large macromolecular complexes composed of ribosomal RNA and proteins. - Techniques like **sucrose gradient centrifugation** or specialized gel electrophoresis (e.g., non-denaturing agarose gels for intact ribosomes) are used to separate ribosomes, not PFGE.

Practice by Chapter

Spectrophotometry and Colorimetry

Practice Questions

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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