Biochemical Techniques Practice Questions

Q: A thin, emaciated 25-year-old male presents with purple plaques and nodules on his face and arms, coughing, and shortness of breath. Which one of the following tests would be most efficient for diagnosing the cause of his problems?

Western blot. ### **Explanation** **Clinical Correlation:** The patient presents with classic signs of **Kaposi Sarcoma** (purple plaques/nodules) and respiratory symptoms (suggestive of *Pneumocystis jirovecii* pneumonia). This clinical triad in a young, emaciated male is highly suspicious for **HIV/AIDS**. **Why Western Blot is Correct:** The **Western blot** is a biochemical technique used to detect specific **proteins** in a sample. Historically, it has been the "gold standard" confirmatory test for HIV diagnosis. It detects antibodies against specific viral proteins (such as gp120, gp41, and p24). While modern 4th-generation ELISA/p24 antigen assays have largely replaced it in routine screening, Western blot remains the classic academic answer for confirming the presence of viral proteins/antibodies in this context. **Why Other Options are Incorrect:** * **Southern Blot:** Used for the detection of specific **DNA** sequences. While it can detect viral DNA integration, it is not the standard or most efficient diagnostic tool for HIV. * **Northern Blot:** Used for the detection of **RNA** sequences. It measures gene expression but is not used for routine clinical diagnosis of HIV. * **Sanger Sequencing:** Used to determine the exact **nucleotide sequence** of DNA. It is used for detecting drug resistance mutations in HIV but is too slow and expensive for primary diagnosis. **High-Yield NEET-PG Pearls:** * **Mnemonic for Blots (SNOW DROP):** * **S**outhern = **D**NA * **N**orthern = **R**NA * **O** = **O** (No match) * **W**estern = **P**rotein * **HIV Diagnosis:** Screening is done by **ELISA** (high sensitivity); Confirmation is done by **Western Blot** (high specificity). * **Kaposi Sarcoma:** Caused by **HHV-8** (Human Herpesvirus 8).

Q: The fastest moving fraction of protein in serum when subjected to paper electrophoresis is?

Albumin. **Explanation:** Serum protein electrophoresis (SPEP) separates proteins based on their **net charge-to-mass ratio** at a specific pH (typically 8.6). At this alkaline pH, all serum proteins carry a net negative charge and migrate toward the positive electrode (anode). **Why Albumin is the correct answer:** Albumin is the fastest-moving fraction because it has the **highest net negative charge** and the **smallest molecular weight** among the major serum proteins. Due to its high charge density, it experiences the greatest electrophoretic mobility, positioning it closest to the anode. **Analysis of Incorrect Options:** * **Alpha 1 Globulin:** These move slower than albumin. This fraction includes proteins like $\alpha_1$-antitrypsin. * **Beta Globulin:** These have a lower net negative charge than alpha globulins and move even slower. Examples include transferrin and complement C3. * **Gamma Globulin:** These are the **slowest-moving** fraction. They have the least negative charge and are located closest to the cathode (negative electrode). In fact, due to a phenomenon called *electroendosmosis*, they may even appear to move slightly toward the cathode. **High-Yield Clinical Pearls for NEET-PG:** * **Order of Mobility (Fastest to Slowest):** Albumin > $\alpha_1$ > $\alpha_2$ > $\beta$ > $\gamma$. * **Pre-albumin (Transthyretin):** If present, it actually moves faster than albumin, but it is usually not visible on standard SPEP due to low concentration. * **Clinical Patterns:** * **Nephrotic Syndrome:** Characterized by a massive decrease in Albumin and a prominent increase in the **$\alpha_2$-macroglobulin** peak. * **Multiple Myeloma:** Shows a sharp, narrow "M-spike" in the **Gamma** region. * **Cirrhosis:** Shows "Beta-Gamma bridging" due to increased IgA.

Q: Which technique is used for the study of the molecular structure of biomolecules?

X-ray crystallography. ### Explanation **Correct Option: C. X-ray crystallography** **Why it is correct:** X-ray crystallography is the gold-standard technique for determining the **three-dimensional molecular structure** of biomolecules at an atomic level. When X-rays strike a crystallized form of a molecule (like a protein or DNA), they are diffracted into a specific pattern. By analyzing the angles and intensities of these diffracted beams, scientists can create an electron density map to determine the precise position of every atom within the molecule. This technique was famously used to discover the double-helix structure of DNA and the structure of hemoglobin. **Why the other options are incorrect:** * **A. Electron microscopy:** This technique is used to visualize the **morphology and ultrastructure** of cells and organelles. While "Cryo-electron microscopy" can study large complexes, standard EM does not provide the atomic-level structural resolution of crystallography. * **B. Ion exchange chromatography:** This is a **separation technique** based on the net surface charge of molecules. It is used to purify proteins or amino acids, not to determine their internal molecular structure. * **D. Agarose gel electrophoresis:** This is a technique used to **separate fragments** of DNA or RNA based on their size and charge. It provides information about the length of the molecule, not its 3D atomic structure. **High-Yield Facts for NEET-PG:** * **NMR Spectroscopy:** Another technique used for molecular structure, but unlike X-ray crystallography, it can study molecules in **aqueous solution** (dynamic state). * **Ramachandran Plot:** Used to validate the structures obtained from X-ray crystallography by plotting the phi ($\phi$) and psi ($\psi$) angles of amino acids. * **Sequencing:** To determine the *primary* structure (amino acid sequence), Sanger’s method or Edman degradation is used.

Q: What is the method of choice for protein identification?

Mass spectrometry. **Explanation:** **Mass Spectrometry (MS)** is currently the "gold standard" and method of choice for protein identification due to its high sensitivity, speed, and ability to analyze complex mixtures. The process involves ionizing protein fragments (peptides) and measuring their mass-to-charge ratio ($m/z$). These mass signatures are then compared against genomic databases to identify the protein with high precision. Modern proteomics relies heavily on techniques like **MALDI-TOF** (Matrix-Assisted Laser Desorption/Ionization-Time of Flight) for rapid identification. **Analysis of Incorrect Options:** * **Edman Technique:** This was the traditional method for N-terminal sequencing. It involves the stepwise removal of amino acids using phenylisothiocyanate. While accurate, it is slow, requires large amounts of pure protein, and cannot sequence proteins with "blocked" N-terminals. * **Sanger Technique:** Historically significant as the first method used to sequence insulin (using 1-fluoro-2,4-dinitrobenzene), it is now obsolete for routine protein identification as it only identifies the N-terminal amino acid. * **2-D Electrophoresis:** This is a **separation** technique, not an identification technique. It separates proteins based on two properties: isoelectric point (pI) in the first dimension and molecular weight (SDS-PAGE) in the second. It is often used *prior* to Mass Spectrometry. **High-Yield Facts for NEET-PG:** * **Sanger’s Reagent:** 1-fluoro-2,4-dinitrobenzene (FDNB). * **Edman’s Reagent:** Phenylisothiocyanate (PITC). * **Proteomics:** The large-scale study of proteins; Mass Spectrometry is its cornerstone. * **Western Blot:** Used for the detection of a *specific* protein using antibodies, but not for de novo identification of unknown proteins.

Q: Which of the following blotting techniques does not exist?

Eastern. **Explanation:** In biochemistry, blotting techniques are used to identify specific macromolecules (DNA, RNA, or proteins) from a complex mixture. The naming convention for these techniques is a mix of eponymous honors and directional puns. **Why "Eastern" is the correct answer:** While Southern, Northern, and Western blots are standard, foundational techniques in molecular biology, **Eastern blotting** is not a primary, universally recognized technique for the detection of a major nucleic acid or protein class. Although some specialized research papers use the term "Eastern blot" to describe the analysis of post-translational modifications (like lipids or carbohydrates), it is **not** considered a standard diagnostic or foundational blotting technique in the context of medical examinations like NEET-PG. **Analysis of Incorrect Options:** * **Southern Blotting:** Named after **Edwin Southern**, this technique is used to detect specific **DNA** sequences. (Mnemonic: **S**outhern = **D**NA). * **Northern Blotting:** A play on the name Southern, this technique is used to detect specific **RNA** molecules to study gene expression. (Mnemonic: **N**orthern = **R**NA). * **Western Blotting:** Used to detect specific **proteins** using antibodies. It is clinically significant as a confirmatory test for HIV (detecting p24 or gp120). (Mnemonic: **W**estern = **P**rotein). **High-Yield NEET-PG Pearls:** * **SNOW DROP Mnemonic:** * **S**outhern — **D**NA * **N**orthern — **R**NA * **O** — (Nothing) * **W**estern — **P**roteins * **Southwestern Blotting:** A legitimate hybrid technique used to identify **DNA-binding proteins** (e.g., transcription factors like c-Jun or c-Fos). * **Clinical Application:** Western blot is the gold standard for confirming **HIV** and **Lyme disease** after initial screening.

Q: Which of the following methods can be used for producing fusion of cells?

Reducing surface tension. **Explanation:** Cell fusion (hybridization) is a critical technique in biotechnology, most notably used in the production of **monoclonal antibodies** via Hybridoma technology. **Why "Reducing Surface Tension" is the correct answer:** The fundamental physical requirement for two cells to fuse is the destabilization of their lipid bilayers. Cell membranes naturally repel each other due to their surface charge and hydration layers. By **reducing the surface tension** at the point of contact, the lipid molecules are rearranged, allowing the membranes to merge and form a single continuous bilayer (syncytium). This is the underlying physical principle behind all chemical and electrical fusion methods. **Analysis of Options:** * **A. Attaching inactive viral particles:** While certain viruses (like the **Sendai virus**) are used as "fusogens," they work by specific protein-mediated membrane fusion, not merely by "attaching" to the membrane. * **B. Adding polyethylene glycol (PEG):** PEG is the most common **chemical fusogen**. It acts by dehydrating the space between cells, but its primary mechanism is the alteration of membrane fluidity and reduction of surface tension. * **C. Applying a small electric current:** Known as **Electrofusion**, this method uses high-voltage pulses to create temporary pores (electroporation), leading to fusion. *Note: While A, B, and C are specific methods/agents, "Reducing surface tension" represents the core biochemical mechanism that facilitates the process.* **High-Yield Clinical Pearls for NEET-PG:** * **Hybridoma Technology:** Developed by Kohler and Milstein; involves fusing a B-lymphocyte with a Myeloma cell. * **Selection Medium:** **HAT Medium** (Hypoxanthine, Aminopterin, Thymidine) is used to select fused hybrid cells. * **Fusogens:** PEG (Chemical), Sendai Virus (Biological), and Electrofusion (Physical) are the three primary categories.

Question 1

A thin, emaciated 25-year-old male presents with purple plaques and nodules on his face and arms, coughing, and shortness of breath. Which one of the following tests would be most efficient for diagnosing the cause of his problems?

Accepted Answer

Western blot

Answer

Southern blot

Answer

Northern blot

Answer

Sanger sequencing

Question 2

The fastest moving fraction of protein in serum when subjected to paper electrophoresis is?

Accepted Answer

Albumin

Answer

Alpha 1 Globulin

Answer

Beta Globulin

Answer

Gamma Globulin

Question 3

What is the most sensitive test for measuring serum hCG levels for the diagnosis of pregnancy?

Accepted Answer

Immuno Radiometric assay

Answer

Serum beta hCG by ELISA

Answer

Urine pregnancy test

Answer

Radio Immunoassay

Question 4

In SDS-PAGE, proteins are separated on the basis of?

Accepted Answer

Molecular weight

Answer

Mass

Answer

Charge

Answer

Density

Question 5

Which technique is used for the study of the molecular structure of biomolecules?

Accepted Answer

X-ray crystallography

Answer

Electron microscopy

Answer

Ion exchange chromatography

Answer

Agarose gel electrophoresis

Question 6

What is the method of choice for protein identification?

Accepted Answer

Mass spectrometry

Answer

Edman technique

Answer

Sanger technique

Answer

2-D electrophoresis

Question 7

Which of the following blotting techniques does not exist?

Accepted Answer

Eastern

Answer

Western

Answer

Southern

Answer

Northern

Question 8

What is the best method to differentiate proteins?

Accepted Answer

Gel chromatography

Answer

Affinity chromatography

Answer

Ion exchange electrophoresis

Answer

None of the above

Question 9

Which of the following methods can be used for producing fusion of cells?

Accepted Answer

Reducing surface tension

Answer

Attaching inactive viral particles on cell membrane

Answer

Adding polyethylene glycol

Answer

Applying a small electric current

Question 10

A protein with a molecular weight of 100 kD is subjected to SDS-PAGE electrophoresis. After the addition of mercaptoethanol, the electrophoresis pattern shows two widely separated bands of 20 kD and 30 kD. Which statement regarding this protein is true?

Accepted Answer

The protein is a dimer composed of 20 kD and 30 kD subunits.

Answer

The protein has undergone complete lysis.

Answer

The protein is a monomer composed of 20 kD and 30 kD subunits.

Answer

The protein is a tetramer composed of 20 kD and 30 kD subunits.

Biochemical Techniques — MCQs

Biochemical Techniques — MCQs

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