Biochemical Techniques Practice Questions

Q: Flow cytometry is performed to determine which of the following parameters?

Rapid cell shrinkage. **Explanation:** **Flow cytometry** is a sophisticated laser-based technology used to analyze the physical and chemical characteristics of particles or cells in a fluid suspension. **Why Option A is Correct:** Flow cytometry measures two primary physical properties as cells pass through a laser beam: 1. **Forward Scatter (FSC):** Correlates with **cell size**. 2. **Side Scatter (SSC):** Correlates with **internal complexity or granularity**. **Rapid cell shrinkage** is a hallmark of **apoptosis** (programmed cell death). During this process, cells lose water and ions, leading to a reduction in volume. In flow cytometry, this is detected as a **decrease in Forward Scatter (FSC)**. Therefore, flow cytometry is a gold-standard technique for quantifying cell size changes and identifying apoptotic populations. **Why the Other Options are Incorrect:** * **Option B & C:** Blood flow to the brain and net oxygen supply to tissues are hemodynamic parameters typically measured using imaging modalities like Functional MRI (fMRI), PET scans, or Doppler ultrasound. * **Option D:** The amount of oxygen bound to hemoglobin is measured via pulse oximetry (SpO2) or arterial blood gas (ABG) analysis. **High-Yield Clinical Pearls for NEET-PG:** * **CD Markers:** Flow cytometry is the primary tool for **Immunophenotyping** (e.g., diagnosing Leukemias and Lymphomas by identifying CD3, CD4, CD8, CD19, etc.). * **HIV Monitoring:** It is used to calculate the absolute **CD4+ T-cell count** to monitor disease progression. * **DNA Analysis:** It can determine **Ploidy** (DNA content) and cell cycle phases using fluorescent dyes like Propidium Iodide. * **Fetal-Maternal Hemorrhage:** The **Kleihauer-Betke test** is being replaced by flow cytometry to quantify fetal RBCs in maternal circulation.

Q: Which of the following is/are applications of FISH?

All the above. **Explanation:** **Fluorescence In Situ Hybridization (FISH)** is a cytogenetic technique that uses fluorescent probes that bind to only those parts of a nucleic acid sequence with a high degree of sequence complementarity. It bridges the gap between molecular biology and cytogenetics. **Why "All the Above" is Correct:** * **Gene Mapping (Option A):** FISH is a primary tool for physical mapping of genes. By using specific fluorescent probes, scientists can visualize the exact location of a gene on a specific chromosome. * **3D Chromosome Organization (Option B):** Unlike traditional karyotyping, FISH can be performed on **interphase nuclei**. This allows researchers to study the spatial arrangement and "territories" of chromosomes within the nucleus, which is crucial for understanding gene regulation. * **Monitoring Bone Marrow Transplantation (Option C):** In sex-mismatched transplants (e.g., male donor to female recipient), FISH for X and Y chromosomes is used to assess **chimerism**. This helps determine if the donor cells have successfully engrafted or if the recipient's cells are returning (relapse). **Clinical Pearls & High-Yield Facts for NEET-PG:** * **Speed:** FISH is faster than traditional karyotyping because it does not require cell culture (can be done on non-dividing interphase cells). * **Resolution:** It has a higher resolution than G-banding, detecting microdeletions (e.g., **22q11 deletion in DiGeorge Syndrome**). * **Common Applications:** * **Aneuploidy:** Rapid screening for Trisomy 13, 18, 21. * **Cancer Genetics:** Detecting the **BCR-ABL fusion** (Philadelphia chromosome) in CML or **HER2/neu** amplification in breast cancer. * **Limitation:** You must know the "target" sequence beforehand to select the correct probe; it is not a "blind" screening tool like a full karyotype.

Q: Which of the following techniques is used to study protein-protein interactions?

Affinity electrophoresis. **Explanation:** **1. Why Affinity Electrophoresis is correct:** Affinity electrophoresis is a specialized technique used to study the **binding interactions** between molecules. It works on the principle that the electrophoretic mobility of a protein changes when it interacts with another molecule (ligand). When a protein binds to another protein (or a specific ligand) within the gel matrix, its migration speed is altered. By observing these shifts in mobility, researchers can determine the **binding constant** and the specificity of **protein-protein interactions**. **2. Why the other options are incorrect:** * **Western Blot:** While it is a gold-standard technique for protein analysis, it is used for the **detection and quantification** of a specific protein in a sample using antibodies. It identifies the presence of a protein but does not inherently measure the interaction between two different proteins in their native state. * **Thin-layer Chromatography (TLC):** This is a separation technique based on differential partitioning between a stationary phase and a mobile phase. It is primarily used for identifying **small molecules** like amino acids, lipids, or drugs, rather than complex macromolecular interactions. **3. High-Yield Clinical Pearls for NEET-PG:** * **Yeast Two-Hybrid System:** Another high-yield technique frequently asked for studying protein-protein interactions *in vivo*. * **Co-Immunoprecipitation (Co-IP):** The "gold standard" for identifying protein complexes from cell lysates. * **Southern Blot = DNA; Northern Blot = RNA; Western Blot = Protein** (Mnemonic: **SNOW DROP**). * **Southwestern Blot:** Used specifically to study **Protein-DNA interactions**.

Q: Which of the following procedures is used to separate and detect DNA fragments?

Southern blotting. **Explanation:** The correct answer is **Southern blotting**. This technique is the gold standard for identifying specific DNA sequences within a complex mixture. **1. Why Southern Blotting is Correct:** Southern blotting (named after Edwin Southern) involves a multi-step process: DNA digestion by restriction endonucleases, separation by size via gel electrophoresis, transfer (blotting) to a nitrocellulose membrane, and finally, **hybridization with a labeled DNA probe**. This allows for both the separation and the specific detection of target DNA fragments. **2. Analysis of Incorrect Options:** * **Northern blotting:** Used for the detection and separation of **RNA** molecules. It is primarily used to study gene expression (mRNA levels). * **Western blotting:** Used for the detection of specific **proteins** using antibodies. It is the confirmatory test for HIV (detecting p24 or gp120/160). * **DNA electrophoresis:** While this technique **separates** DNA fragments based on size and charge, it does not inherently **detect** a specific sequence unless followed by a blotting or staining procedure (like Ethidium Bromide). Southern blotting is the complete procedure for both separation and specific identification. **3. High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic (SNOW DROP):** * **S**outhern = **D**NA * **N**orthern = **R**NA * **O**oo = **O**oo (Placeholder) * **W**estern = **P**rotein * **Southwestern Blotting:** A hybrid technique used to detect **DNA-binding proteins** (e.g., transcription factors like c-Jun or c-Fos). * **Clinical Application:** Southern blotting is used in DNA fingerprinting, detecting gene mutations (e.g., sickle cell anemia), and identifying viral integration into host DNA.

Q: Which color in Benedict's test indicates that no reducing sugar is present?

Blue. **Explanation:** **Benedict’s test** is a semi-quantitative chemical assay used to detect the presence of **reducing sugars** (such as glucose, fructose, galactose, lactose, and maltose). The reagent contains cupric ions ($Cu^{2+}$) in the form of copper sulfate, which gives the solution its characteristic **deep blue color**. 1. **Why Blue is Correct:** When the reagent is heated with a sample, reducing sugars (which have a free aldehyde or ketone group) reduce the blue cupric ions ($Cu^{2+}$) to insoluble red cuprous oxide ($Cu_2O$). If **no reducing sugar** is present, no reduction occurs, the copper remains in its cupric state, and the solution stays **Blue**. This represents a negative result. 2. **Why Other Options are Incorrect:** The color change in Benedict's test follows a gradient based on the concentration of reducing sugar: * **Green (Option B):** Indicates a trace amount of reducing sugar (approx. 0.5–1.0 g%). * **Orange (Option C):** Indicates a moderate amount of reducing sugar (approx. 1.5–2.0 g%). * **Brick Red (Option D):** Indicates a high concentration of reducing sugar (>2.0 g%). **High-Yield Clinical Pearls for NEET-PG:** * **Non-reducing sugars:** **Sucrose** is the most common non-reducing sugar and will give a negative (Blue) Benedict’s test because its glycosidic bond involves both anomeric carbons, leaving no free aldehyde or ketone group. * **Clinical Use:** Historically used to detect glucose in urine (**Glucosuria**), a hallmark of Diabetes Mellitus. * **False Positives:** Can occur with high levels of ascorbic acid (Vitamin C), urates, or certain drugs like salicylates and cephalosporins. * **Benedict’s vs. Fehling’s:** Benedict’s reagent is more stable and more sensitive than Fehling’s solution.

Q: Gel filtration chromatography separates proteins based on which property?

Stokes radius. ### Explanation **Correct Answer: C. Stokes radius** **Mechanism of Action:** Gel filtration chromatography, also known as **Size-Exclusion Chromatography (SEC)**, separates molecules based on their size and shape. The stationary phase consists of porous beads (e.g., Sephadex). * **Small molecules** enter the pores of the beads, increasing their path length and slowing their movement. * **Large molecules** are excluded from the pores and travel only through the void volume between beads, eluting **first**. The effective size of a molecule in solution, which determines its ability to enter these pores, is termed the **Stokes radius**. While molecular weight is often used as a proxy, the Stokes radius accounts for the hydration shell and the 3D shape of the protein. **Why Other Options are Incorrect:** * **A. Polarity:** Separation based on polarity is the principle of **Normal Phase or Partition Chromatography**. * **B. Hydrophobicity:** This is the basis for **Hydrophobic Interaction Chromatography (HIC)** or Reverse-Phase HPLC. * **D. pH:** While pH affects a protein's charge, separation based on charge (isoelectric point) is the principle of **Ion Exchange Chromatography** or Isoelectric Focusing. **High-Yield NEET-PG Pearls:** 1. **Elution Order:** In Gel Filtration, the **largest** proteins elute first, and the **smallest** elute last. 2. **Applications:** It is commonly used for **desalting** a protein solution (removing small salt ions) and determining the quaternary structure (molecular weight) of proteins. 3. **Void Volume ($V_0$):** The volume of the mobile phase outside the gel beads. Large molecules elute at $V_0$. 4. **Comparison:** Do not confuse this with **SDS-PAGE**, where smaller proteins move faster; in Gel Filtration, larger proteins move faster.

Q: Two proteins with the same charge can be separated by which of the following methods?

Sephadex gel filtration chromatography. ### Explanation The separation of proteins depends on exploiting differences in their physical and chemical properties, such as size, net charge, or binding affinity. **Why Sephadex gel filtration chromatography is correct:** Sephadex gel filtration (also known as **Size-Exclusion Chromatography**) separates proteins based on their **molecular weight and size (hydrodynamic radius)**, not their charge. The stationary phase consists of porous beads. Large molecules cannot enter the pores and elute first (void volume), while smaller molecules enter the pores, follow a longer path, and elute later. Therefore, if two proteins have the same charge but different sizes, this technique will effectively separate them. **Why the other options are incorrect:** * **Agarose gel electrophoresis:** This technique separates molecules primarily based on their **charge-to-mass ratio**. If two proteins have the same net charge and similar shapes, they are unlikely to separate effectively in a standard electrophoretic field. * **DEAE-Cellulose chromatography:** This is a type of **Anion Exchange Chromatography**. It separates proteins based on their **net surface charge**. Proteins with the same charge would have similar binding affinities to the positively charged DEAE matrix and would elute together, making separation impossible. **High-Yield NEET-PG Pearls:** * **Molecular Sieving:** Another name for Gel Filtration. * **Elution Order:** In Gel Filtration, **Large** proteins elute **First**; in SDS-PAGE (electrophoresis), **Small** proteins migrate **Fastest**. * **SDS-PAGE:** Unlike native electrophoresis, SDS-PAGE separates proteins solely by **mass** because the detergent SDS coats proteins with a uniform negative charge, masking their intrinsic charge. * **Isoelectric Focusing (IEF):** Separates proteins based on their **isoelectric point (pI)**.

Q: The Southern blot test is used for the detection of which of the following?

DNA. **Explanation:** The **Southern blot** is a fundamental molecular biology technique used to detect specific **DNA** sequences within a complex mixture of genomic DNA. The process involves four key steps: (1) Digestion of DNA using restriction endonucleases, (2) Separation of fragments by size via gel electrophoresis, (3) Transfer (blotting) of the DNA onto a nitrocellulose or nylon membrane, and (4) Hybridization with a labeled, sequence-specific DNA probe for visualization. **Analysis of Options:** * **Option B (DNA):** This is the correct answer. Named after Edwin Southern, this technique is the gold standard for identifying gene mutations, deletions, or insertions (e.g., detecting Sickle Cell Anemia or Fragile X syndrome). * **Option C (RNA):** RNA is detected using the **Northern blot**. This technique measures gene expression levels by identifying specific mRNA sequences. * **Option A (Antibodies/Proteins):** Proteins (including antibodies) are detected using the **Western blot**. This is clinically significant as a confirmatory test for HIV (detecting antibodies against viral proteins like p24 or gp120). * **Option D (Carbohydrate epitopes):** While less common, the detection of carbohydrates or lipids is sometimes referred to as **Eastern blotting** (though this term is also used for post-translational modifications of proteins). **High-Yield Clinical Pearls for NEET-PG:** * **Mnemonic (SNOW DROP):** * **S**outhern = **D**NA * **N**orthern = **R**NA * **O** = **O** (No technique) * **W**estern = **P**rotein * **Southwestern Blot:** Used specifically to detect **DNA-binding proteins** (e.g., transcription factors like c-Jun or c-Fos). * **Application:** Southern blotting is used in **RFLP (Restriction Fragment Length Polymorphism)** analysis for forensic "DNA fingerprinting" and prenatal diagnosis of genetic disorders.

Q: All of the following assays are used for estimation of total serum protein, except?

Bromocresol green. ### Explanation The estimation of serum proteins is a fundamental biochemical analysis. The key to this question lies in distinguishing between methods that measure **total protein** versus those specific to **albumin**. **Why Bromocresol Green (BCG) is the correct answer:** Bromocresol green is a dye-binding technique specifically used for the **quantitation of Serum Albumin**, not total protein. At a slightly acidic pH, albumin acts as a cation and binds to the anionic BCG dye, causing a color shift from yellow-green to blue-green. It is the most common automated method for albumin due to its speed and specificity. **Analysis of incorrect options (Total Protein Methods):** * **Biuret Method (Option A):** The gold standard and most common method for **Total Protein**. It relies on copper ions ($Cu^{2+}$) forming a violet-colored complex with peptide bonds in an alkaline medium. It requires at least two peptide bonds to react. * **Lowry’s Method (Option C):** A highly sensitive method combining the Biuret reaction with the reduction of the **Folin-Ciocalteu reagent** by aromatic amino acids (Tyrosine and Tryptophan). It is used for dilute protein solutions. * **Bradford Assay (Option B):** A rapid method based on the binding of **Coomassie Brilliant Blue G-250** dye to proteins. The dye shifts its absorption maximum from 465 nm to 595 nm upon binding to protein (primarily basic and aromatic residues). **Clinical Pearls for NEET-PG:** * **A/G Ratio:** Total Protein minus Albumin gives the **Globulin** fraction. A reversed A/G ratio (normal 1.2:1 to 2:1) is seen in Multiple Myeloma and Chronic Liver Disease. * **Kjeldahl Method:** The reference method for total protein based on nitrogen content, though too cumbersome for routine clinical use. * **Bence-Jones Proteins:** Detected via heat precipitation or electrophoresis, not standard Biuret/BCG methods.

Question 1

The molecular weight of a protein can be determined by which of the following methods?

Accepted Answer

Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE)

Answer

Native polyacrylamide gel electrophoresis (PAGE)

Answer

Isoelectric focusing

Answer

Ion exchange chromatography

Question 2

Flow cytometry is performed to determine which of the following parameters?

Accepted Answer

Rapid cell shrinkage

Answer

Blood flow to the brain

Answer

Net oxygen supply to tissues

Answer

Amount of oxygen bound to hemoglobin

Question 3

Which of the following is/are applications of FISH?

Accepted Answer

All the above

Answer

Gene mapping

Answer

Study of 3D chromosome organization in interphase nuclei

Answer

Monitoring the success of bone marrow transplantation

Question 4

Which of the following techniques is used to study protein-protein interactions?

Accepted Answer

Affinity electrophoresis

Answer

Western blot

Answer

Thin-layer chromatography

Answer

None of the above

Question 5

Which of the following procedures is used to separate and detect DNA fragments?

Accepted Answer

Southern blotting

Answer

Northern blotting

Answer

Western blotting

Answer

DNA electrophoresis

Question 6

Which color in Benedict's test indicates that no reducing sugar is present?

Accepted Answer

Blue

Answer

Green

Answer

Orange

Answer

Brick red

Question 7

Gel filtration chromatography separates proteins based on which property?

Accepted Answer

Stokes radius

Answer

Polarity

Answer

Hydrophobicity

Answer

pH

Question 8

Two proteins with the same charge can be separated by which of the following methods?

Accepted Answer

Sephadex gel filtration chromatography

Answer

Agarose gel electrophoresis

Answer

DEAE-Cellulose chromatography

Answer

None of the above

Question 9

The Southern blot test is used for the detection of which of the following?

Accepted Answer

DNA

Answer

Antibodies against viral proteins

Answer

RNA

Answer

Carbohydrate epitopes

Question 10

All of the following assays are used for estimation of total serum protein, except?

Accepted Answer

Bromocresol green

Answer

Biuret

Answer

Bradford

Answer

Lowry's

Biochemical Techniques — MCQs

Biochemical Techniques — MCQs

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