Biochemical Techniques Practice Questions

Q: Which of the following statements is true regarding High-Performance Liquid Chromatography (HPLC) and Gas Chromatography?

In Gas Chromatography, the mobile phase is always gas.. **Explanation:** Chromatography is a fundamental biochemical technique used to separate components of a mixture based on their relative affinities for a **stationary phase** and a **mobile phase**. **1. Why Option D is Correct:** In **Gas Chromatography (GC)**, the mobile phase is strictly an inert carrier gas (such as Helium, Nitrogen, or Argon). Its primary role is to transport the volatile sample through the column. Since the separation depends on the sample being in a vapor state, the mobile phase must be gaseous. **2. Analysis of Incorrect Options:** * **Option A:** In GC, the stationary phase can be either a **solid** (Gas-Solid Chromatography) or a **liquid** coated on a solid support (Gas-Liquid Chromatography). Therefore, it is not "always" solid. * **Option B:** In **HPLC**, the stationary phase is typically a solid (silica-based) or a liquid film bonded to solid particles. However, the defining feature of HPLC is the high pressure applied to the liquid mobile phase, not just the state of the stationary phase. * **Option C:** In HPLC, the mobile phase is **always a liquid** (solvent). It can never be a solid, as it must flow through the packed column under high pressure. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **HPLC Use:** It is the "Gold Standard" for the estimation of **HbA1c** (Glycated Hemoglobin) and for screening hemoglobinopathies (e.g., Thalassemia). * **GC Use:** Primarily used for detecting **volatile compounds**, such as blood alcohol levels, fatty acids, and toxicology screens. * **Key Difference:** GC requires the sample to be volatile and thermally stable, whereas HPLC can analyze non-volatile, polar, and thermally unstable biological molecules (like proteins and drugs).

Q: Cells can be separated based on specific antigen receptors using which technique?

Flow cytometry. **Explanation:** **Why Flow Cytometry is correct:** Flow cytometry is a sophisticated technique used to analyze and sort cells based on their physical and chemical characteristics. The core principle involves labeling cells with **fluorescently-tagged monoclonal antibodies** that bind to specific **antigen receptors** (surface markers or Cluster of Differentiation/CD markers). As cells pass in a single-file stream through a laser beam, the light scattering and fluorescence emission are measured. A specialized version, **FACS (Fluorescence-Activated Cell Sorting)**, physically separates these cells into different containers based on their specific antigenic profile. **Why other options are incorrect:** * **Enzyme-based methods:** These are typically used for biochemical assays (like ELISA) to detect proteins or metabolites, but they are not used for the physical separation of intact cells based on surface receptors. * **Electrophoresis:** This technique separates molecules (DNA, RNA, or proteins) based on their **size and charge** in an electric field, not whole cells based on antigen receptors. * **G-banding:** This is a cytogenetic technique used to stain condensed chromosomes (using Giemsa stain) to visualize banding patterns for detecting structural abnormalities; it has no role in cell separation. **High-Yield Clinical Pearls for NEET-PG:** * **Clinical Utility:** Flow cytometry is the gold standard for **immunophenotyping** in leukemias and lymphomas and for monitoring **CD4+ T-cell counts** in HIV/AIDS patients. * **Parameters:** It measures **Forward Scatter (FSC)**, which indicates cell size, and **Side Scatter (SSC)**, which indicates internal complexity or granularity. * **FACS:** Remember that FACS is a specific type of flow cytometry that allows for the physical collection (sorting) of a specific cell population for further study.

Q: Which assay is considered the most accurate for assessing hormone levels?

Radioimmunoassay (RIA). ### Explanation **Correct Answer: D. Radioimmunoassay (RIA)** **Why RIA is the Correct Answer:** Radioimmunoassay (RIA) is considered the gold standard for hormone quantification due to its **extreme sensitivity and specificity**. It utilizes the principle of **competitive binding**, where a labeled antigen (radioisotope-tagged hormone) and an unlabeled antigen (patient’s hormone) compete for a limited number of antibody binding sites. Because RIA can detect substances at picomolar and nanomolar concentrations ($10^{-12}$ to $10^{-9}$ g/mL), it is uniquely suited for measuring hormones that circulate in minute quantities, such as TSH, insulin, and steroid hormones. **Why Other Options are Incorrect:** * **A. Flow Cytometry:** Primarily used for cell counting, cell sorting, and detecting biomarkers on cell surfaces (e.g., CD4/CD8 counts in HIV). It is not used for quantifying dissolved hormones in serum. * **B. Electrophoresis:** A technique used to separate molecules (proteins, DNA, RNA) based on their size and charge. While it can identify protein fractions (e.g., albumin, globulins), it lacks the sensitivity required for precise hormone quantification. * **C. ELISA:** While ELISA is widely used in clinical labs because it avoids radioactive waste, RIA remains technically superior in terms of sensitivity for very low-level hormone detection. ELISA is often the "preferred" screening method, but RIA is historically the most "accurate" for minute concentrations. **High-Yield Clinical Pearls for NEET-PG:** * **RIA Principle:** Competitive inhibition/binding. * **Isotope used:** Iodine-125 ($^{125}I$) is the most common radioisotope used in RIA. * **Scatchard Plot:** Used in RIA to calculate the affinity constant of the antibody. * **B/F Ratio:** In RIA, as the concentration of the patient's (unlabeled) hormone increases, the ratio of Bound-to-Free (B/F) labeled hormone decreases.

Q: Method of chromatography in which molecules that are negatively charged are selectively released from the stationary phase by positively charged molecules in the mobile phase is termed as?

Ion-Exchange chromatography. **Explanation:** **Ion-Exchange Chromatography (IEC)** is a technique that separates molecules based on their net surface charge. The stationary phase consists of an insoluble matrix (resin) containing immobilized charged groups. * In **Anion-Exchange Chromatography**, the stationary phase is positively charged and binds negatively charged molecules (anions). * To release (elute) these bound molecules, a mobile phase containing competing positively charged ions or a change in pH is used. The question describes this specific mechanism where charged interactions dictate the separation, making Option B the correct answer. **Why other options are incorrect:** * **Affinity Chromatography:** Relies on highly specific biological interactions, such as antigen-antibody, enzyme-substrate, or receptor-ligand binding, rather than simple ionic charge. * **Adsorption Chromatography:** Separation is based on the differential exploitation of the physical adsorption of solutes on the surface of a solid stationary phase (e.g., Silica gel). * **Size-Exclusion Chromatography (Gel Filtration):** Separates molecules based on their hydrodynamic volume (size and shape). Larger molecules elute first as they are excluded from the pores of the stationary phase. **High-Yield Clinical Pearls for NEET-PG:** * **HbA1c Estimation:** Ion-exchange chromatography is the gold standard principle used in HPLC (High-Performance Liquid Chromatography) for measuring glycated hemoglobin. * **Amino Acid Analysis:** IEC is frequently used to separate and quantify amino acids in metabolic screening (e.g., diagnosing Phenylketonuria). * **Cation Exchangers:** Examples include Carboxymethyl (CM) cellulose. * **Anion Exchangers:** Examples include Diethylaminoethyl (DEAE) cellulose.

Q: Which of the following labels corresponds to the condenser of the microscope?

C. ***C*** - The **condenser** is located beneath the **microscope stage** and above the **light source**, which matches the position of label C in the diagram. - Its primary function is to **focus and concentrate light** onto the specimen, improving illumination and image contrast. *B* - Label B typically corresponds to the **stage** where the specimen slide is placed, not the condenser. - The stage is positioned above the condenser and serves as the **specimen platform**. *D* - Label D usually represents the **objective lenses** or **eyepiece**, which are involved in **magnification** rather than light concentration. - These components are located above the stage, opposite to the condenser's position. *A* - Label A commonly indicates the **light source** or **diaphragm**, which are positioned below the condenser. - These components provide **illumination** or control **light intensity**, but do not focus light like the condenser.

Q: Protein is purified using ammonium sulfate by which method?

Salting out. ### Explanation **1. Why "Salting Out" is Correct:** Salting out is a technique used to purify proteins based on their **solubility**. When high concentrations of neutral salts like **Ammonium Sulfate** $(NH_4)_2SO_4$ are added to a protein solution, the salt ions compete with the protein molecules for water molecules (solvation). As the salt concentration increases, the water molecules are "stripped" away from the protein's surface to hydrate the salt ions. This exposes the hydrophobic patches of the proteins, causing them to aggregate and precipitate out of the solution. Ammonium sulfate is the preferred reagent because of its high solubility and low toxicity to protein structure. **2. Why Other Options are Incorrect:** * **Ion Exchange Chromatography:** This technique separates proteins based on their **net surface charge** at a specific pH using stationary phases like DEAE-cellulose (anion exchange) or CM-cellulose (cation exchange). * **Mass Chromatography (Mass Spectrometry):** This is used to determine the **molecular mass** and chemical structure of a protein by measuring the mass-to-charge ratio of ions, rather than for bulk purification. * **Molecular Size Exclusion (Gel Filtration):** This separates proteins based on their **molecular weight/size** using porous beads. Smaller molecules get trapped in the beads and move slowly, while larger molecules elute first. **3. High-Yield Clinical Pearls for NEET-PG:** * **Dialysis:** After salting out, dialysis is the mandatory next step to remove the excess salt from the protein sample. * **Hofmeister Series:** This ranks ions based on their ability to salt out proteins; Sulfate $(SO_4^{2-})$ is a powerful "kosmotrope" (stabilizer) used in this process. * **Specific Activity:** During purification, as you remove unwanted proteins, the *specific activity* (units of enzyme per mg of total protein) should **increase**, indicating successful purification.

Q: All of the following techniques can be used to determine protein structure, EXCEPT:

High-performance liquid chromatography (HPLC). **Explanation:** The determination of protein structure involves analyzing the spatial arrangement of atoms (tertiary and quaternary structure). **Why HPLC is the correct answer:** **High-performance liquid chromatography (HPLC)** is primarily a **separation and purification technique**. It separates proteins or peptides based on their physical properties such as size, charge, or hydrophobicity. While it can be used for quantitative analysis or to check purity, it cannot provide information regarding the three-dimensional folding or atomic coordinates of a protein. **Analysis of incorrect options:** * **X-ray Crystallography:** This is the "gold standard" for determining the 3D structure of proteins at atomic resolution. It requires the protein to be crystallized and uses diffraction patterns to map electron density. * **Nuclear Magnetic Resonance (NMR) Spectrometry:** This technique is used to determine the structure of smaller proteins in **aqueous solution**, making it ideal for studying protein dynamics and folding in a physiological-like state. * **Mass Spectrometry (MS):** While traditionally used for sequencing (primary structure) and determining molecular weight, advanced MS techniques (like Hydrogen-Deuterium Exchange) are now integral in studying protein conformation and folding. **High-Yield NEET-PG Pearls:** * **X-ray Crystallography** requires crystals; **NMR** works for proteins in solution. * **Cryo-electron microscopy (Cryo-EM)** is an emerging high-yield technique for visualizing large macromolecular complexes that are difficult to crystallize. * **Circular Dichroism (CD)** is a common technique used specifically to determine the **secondary structure** (alpha-helices and beta-sheets) of proteins. * **Sanger’s Reagent** (1-fluoro-2,4-dinitrobenzene) is used for N-terminal amino acid sequencing.

Question 1

Which of the following statements is true regarding High-Performance Liquid Chromatography (HPLC) and Gas Chromatography?

Accepted Answer

In Gas Chromatography, the mobile phase is always gas.

Answer

In Gas Chromatography, the stationary phase is always solid.

Answer

In HPLC, the stationary phase is solid.

Answer

In HPLC, the mobile phase is a liquid or solid.

Question 2

Cells can be separated based on specific antigen receptors using which technique?

Accepted Answer

Flow cytometry

Answer

Enzyme-based methods

Answer

Electrophoresis

Answer

G-banding

Question 3

What is the method used to locate the isoelectric point of a protein?

Accepted Answer

Isoelectric point

Answer

Isoelectric focusing

Answer

Ion exchange chromatography

Answer

pH gradient

Question 4

If a radioimmunoassay is properly conducted and the amount of radioactive hormone bound to antibody is low, what would this result indicate?

Accepted Answer

Plasma levels of endogenous hormone are high

Answer

Plasma levels of endogenous hormone are low

Answer

More antibody is needed

Answer

Less radioactive hormone is needed

Question 5

Which assay is considered the most accurate for assessing hormone levels?

Accepted Answer

Radioimmunoassay (RIA)

Answer

Flow cytometry

Answer

Electrophoresis

Answer

Enzyme-linked immunosorbent assay (ELISA)

Question 6

Method of chromatography in which molecules that are negatively charged are selectively released from the stationary phase by positively charged molecules in the mobile phase is termed as?

Accepted Answer

Ion-Exchange chromatography

Answer

Affinity chromatography

Answer

Adsorption chromatography

Answer

Size-Exclusion chromatography

Question 7

Which of the following labels corresponds to the condenser of the microscope?

Accepted Answer

C

Answer

B

Answer

D

Answer

A

Question 8

Which of the following methods most accurately estimates blood creatinine level?

Accepted Answer

Enzyme assay

Answer

Jaffe method

Answer

Kinetic Jaffe method

Answer

Technicon method

Question 9

Protein is purified using ammonium sulfate by which method?

Accepted Answer

Salting out

Answer

Ion exchange chromatography

Answer

Mass chromatography

Answer

Molecular size exclusion

Question 10

All of the following techniques can be used to determine protein structure, EXCEPT:

Accepted Answer

High-performance liquid chromatography (HPLC)

Answer

Mass spectrometry

Answer

X-ray crystallography

Answer

Nuclear magnetic resonance (NMR) spectrometry

Biochemical Techniques — MCQs

Biochemical Techniques — MCQs

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