Biochemical Techniques Practice Questions

Q: The graph below depicts a polymerase chain reaction. What type of PCR is shown?

Real-time PCR. ***Real-time PCR*** - The **sigmoidal amplification curve** showing fluorescence intensity vs cycle number with a **threshold (Ct) value** is characteristic of real-time PCR. - This technique allows **continuous monitoring** of DNA amplification during the reaction using fluorescent reporters like **SYBR Green** or **TaqMan probes**. *DNA PCR* - This is a general term that encompasses all PCR types that amplify DNA, not a specific technique. - It doesn't describe the **real-time monitoring capability** shown in the graph with fluorescence detection. *Standard PCR* - Uses **gel electrophoresis** for end-point detection after all cycles are complete, not during the reaction. - Does not produce a **real-time amplification curve** or measure fluorescence during thermal cycling. *Nested PCR* - Involves **two rounds of amplification** with different primer sets to increase specificity and sensitivity. - Uses **gel electrophoresis** for detection and does not generate real-time fluorescence curves during amplification.

Q: In mass spectrometry, peptides are studied by projection of what?

Hydrogen ion. **Explanation:** **1. Why Hydrogen Ion is Correct:** Mass Spectrometry (MS) is a powerful analytical technique used to identify and quantify proteins and peptides by measuring their **mass-to-charge (m/z) ratio**. For a peptide to be detected and "projected" through the mass analyzer, it must first be ionized (given an electrical charge). In biological mass spectrometry (using techniques like MALDI or ESI), peptides are typically ionized by **protonation**—the addition of one or more **Hydrogen ions (H⁺)**. These positively charged ions are then accelerated by an electric field toward the detector. Without the charge provided by the hydrogen ion, the neutral peptide molecule cannot be manipulated or measured by the electromagnetic fields of the spectrometer. **2. Why Other Options are Incorrect:** * **Helium (A):** Helium is an inert gas often used as a "carrier gas" in Gas Chromatography (GC), but it is not the entity projected to represent the peptide itself in MS. * **Oxygen (C):** Oxygen is not used for ionization in peptide mass spectrometry. In fact, oxygen is often excluded from the system to prevent unwanted oxidation of the sample. * **None of the above (D):** This is incorrect because Hydrogen ions are the fundamental basis for the "soft ionization" processes used in proteomics. **3. High-Yield Clinical Pearls for NEET-PG:** * **Soft Ionization:** Techniques like **MALDI** (Matrix-Assisted Laser Desorption/Ionization) and **ESI** (Electrospray Ionization) are "soft" because they ionize large biomolecules without breaking their covalent bonds. * **Proteomics:** Mass spectrometry is the gold standard for **proteomics**, used clinically for neonatal screening of inborn errors of metabolism (e.g., Tandem MS) and identifying bacterial species in microbiology (MALDI-TOF). * **Key Formula:** Remember that MS measures the **m/z ratio**, not the absolute mass. Adding a Hydrogen ion increases the mass by ~1 Da and the charge by +1.

Q: Which of the following compounds is luminous?

Porphyrin. **Explanation:** **Why Porphyrin is the Correct Answer:** Porphyrins are cyclic tetrapyrroles characterized by a highly conjugated system of double bonds. This chemical structure allows them to absorb light at specific wavelengths (notably the **Soret band** around 400 nm) and emit it at longer wavelengths. When exposed to ultraviolet (UV) light, porphyrins emit a characteristic **intense red fluorescence**. This "luminous" property is a key diagnostic feature used in clinical biochemistry to detect porphyrins in urine, stool, or red blood cells. **Analysis of Incorrect Options:** * **B. Zymogen:** These are inactive precursors of enzymes (e.g., pepsinogen). They do not possess the conjugated ring systems required for fluorescence. * **C. Chromatin:** This is a complex of DNA and proteins (histones). While DNA can be stained with fluorescent dyes (like Ethidium Bromide), it is not inherently luminous or fluorescent on its own. * **D. Albumin:** The most abundant plasma protein. While it has some intrinsic fluorescence due to aromatic amino acids (Tryptophan), it is not considered a "luminous compound" in the clinical or biochemical context compared to the vivid fluorescence of porphyrins. **Clinical Pearls for NEET-PG:** * **Wood’s Lamp Examination:** Used to detect porphyrins in the urine of patients with Porphyria Cutanea Tarda (PCT); the urine glows pink-red under UV light. * **Heme Synthesis:** Porphyrins are intermediates in heme synthesis. Accumulation due to enzyme deficiencies leads to various **Porphyrias**. * **Photosensitivity:** The same property that causes fluorescence also causes tissue damage; porphyrins in the skin react with sunlight to generate free radicals, leading to blistering and scarring.

Q: Who invented Polymerase Chain Reaction (PCR)?

Kary Mullis. **Explanation:** **Correct Answer: B. Kary Mullis** The Polymerase Chain Reaction (PCR) was invented by **Kary Mullis** in 1983. PCR is a revolutionary molecular biology technique used to amplify specific DNA sequences in vitro. It relies on thermal cycling, consisting of cycles of repeated heating and cooling for DNA melting and enzymatic replication. For this groundbreaking invention, Mullis was awarded the **Nobel Prize in Chemistry in 1993**. **Analysis of Incorrect Options:** * **A. Alec Jeffreys:** He is known for developing the techniques for **DNA Fingerprinting** and DNA profiling, which are essential in forensic science. * **C. Cesar Milstein:** Along with Georges Köhler, he developed the hybridoma technology used for the production of **Monoclonal Antibodies**. * **D. Gall and Pardue:** They are credited with the development of **In-situ Hybridization**, a technique used to localize specific nucleic acid sequences within biological samples. **High-Yield Clinical Pearls for NEET-PG:** * **Components of PCR:** Requires a DNA template, Primers (forward and reverse), dNTPs (nucleotides), and a heat-stable DNA polymerase (most commonly **Taq Polymerase** derived from *Thermus aquaticus*). * **Steps of PCR:** 1. **Denaturation** (~94-96°C) 2. **Annealing** (~50-65°C) 3. **Extension** (~72°C) * **RT-PCR:** Reverse Transcriptase PCR is used to amplify RNA sequences (e.g., diagnosing **SARS-CoV-2** or HIV viral load). * **Real-Time PCR (qPCR):** Used for the quantitative measurement of DNA/RNA in a sample.

Q: Introduction of DNA into cells with the help of electricity is known as?

Electroporation. **Explanation:** **Electroporation** (also known as electropermeabilization) is a molecular biology technique that uses an **external electric field** to increase the permeability of the cell membrane. When high-voltage pulses are applied, they temporarily disrupt the phospholipid bilayer, creating microscopic pores (nanopores). This allows hydrophilic molecules like DNA, which normally cannot cross the hydrophobic membrane, to enter the cell. Once the electric field is removed, the pores reseal, trapping the DNA inside. **Analysis of Options:** * **Electrotransfer:** While often used interchangeably with "electrophoretic transfer" (like in Western Blotting), it refers to the movement of molecules from a gel to a membrane, not specifically the introduction of DNA into living cells. * **Electrofusion:** This is the use of electric currents to induce the fusion of two different cells (e.g., creating hybridomas for monoclonal antibody production). * **Electrolysis:** This is a chemical process that uses direct electric current to drive a non-spontaneous chemical reaction (e.g., splitting water into hydrogen and oxygen); it is not a gene transfer technique. **High-Yield Clinical Pearls for NEET-PG:** * **Transformation vs. Transfection:** Electroporation is a method of **transfection** (introducing nucleic acids into eukaryotic cells) or **transformation** (into bacteria). * **Applications:** It is widely used in creating **transgenic animals**, gene therapy, and producing recombinant proteins (like Insulin). * **Other Gene Transfer Methods:** * *Chemical:* Calcium Phosphate precipitation. * *Physical:* Microinjection, Biolistics (Gene gun). * *Biological:* Viral vectors (Retrovirus, Adenovirus).

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: The number of gram equivalents in 1 litre of a solution is known as:

Normality. ### Explanation **Correct Answer: C. Normality** **1. Why Normality is Correct:** Normality (N) is defined as the number of **gram equivalents** of a solute dissolved in **one litre** of solution. In biochemistry and clinical medicine, normality is particularly important when dealing with acid-base reactions and redox titrations because it accounts for the "reactive capacity" of a molecule. * **Formula:** $N = \frac{\text{Gram equivalents of solute}}{\text{Volume of solution in Litres}}$ * **Medical Concept:** One equivalent of an acid is the amount that can donate one mole of $H^+$ ions. For example, a 1M solution of $H_2SO_4$ is 2N because each molecule provides two protons. **2. Why Other Options are Incorrect:** * **A. Molarity (M):** This refers to the number of **moles** of solute per litre of solution. It measures concentration based on molecular count rather than reactive equivalents. * **B. Molality (m):** This is the number of moles of solute per **kilogram of solvent**. Unlike molarity and normality, molality is independent of temperature because it is based on mass, not volume. * **D. None of the above:** Incorrect, as Normality is the standard definition for gram equivalents per litre. **3. High-Yield Clinical Pearls for NEET-PG:** * **Relationship:** $\text{Normality} = \text{Molarity} \times \text{Valency factor (n-factor)}$. * **Temperature Sensitivity:** Since Normality and Molarity are volume-dependent, they **change with temperature**. Molality does not. * **Clinical Application:** In clinical labs, electrolytes are often expressed in **mEq/L** (milliequivalents per litre), which is a sub-unit of Normality. For example, the normal serum concentration of Sodium is 135–145 mEq/L. * **Osmolarity vs. Osmolality:** In human physiology, **Osmolality** (mOsm/kg) is preferred over Osmolarity (mOsm/L) because it is more accurate in biological systems where temperature and pressure fluctuate.

Q: Electrophoresis done under pH gradient is called?

Isoelectric. **Explanation:** The correct answer is **Isoelectric Focusing (IEF)**. **1. Why Isoelectric is Correct:** Isoelectric focusing is a specialized electrophoretic technique used to separate amphoteric molecules, such as proteins, based on their **isoelectric point (pI)** [1], [2]. In this method, a stable **pH gradient** is established in a gel (usually using synthetic carrier ampholytes) [1], [2]. When an electric field is applied, proteins migrate through the gradient until they reach the specific pH zone that matches their pI [1]. At this point, the protein has no net charge (it becomes a zwitterion), stops moving, and "focuses" into a sharp band [2]. **2. Why Other Options are Incorrect:** * **Isoosmotic:** This term refers to solutions having the same osmotic pressure. It is a physiological concept related to fluid balance and tonicity, not a technique for separating molecules via electricity. * **Ion exchange:** This refers to **Ion Exchange Chromatography**, which separates molecules based on their surface charge using a stationary phase (resin) [3]. While it involves charge, it does not utilize a pH gradient or electrophoresis to move the molecules. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **High Resolution:** IEF is one of the most sensitive methods for protein separation, capable of distinguishing proteins that differ by as little as 0.01 pH units in their pI. * **2D-Electrophoresis:** This is a high-yield exam topic. It combines two techniques: **1st Dimension** is Isoelectric Focusing (separation by pI) and **2nd Dimension** is SDS-PAGE (separation by molecular weight) [1], [2]. * **Clinical Application:** IEF is the "Gold Standard" for detecting **oligoclonal bands** in cerebrospinal fluid (CSF), which is a critical diagnostic marker for **Multiple Sclerosis**.

Question 1

The graph below depicts a polymerase chain reaction. What type of PCR is shown?

Accepted Answer

Real-time PCR

Answer

DNA PCR

Answer

Standard PCR

Answer

Nested PCR

Question 2

In mass spectrometry, peptides are studied by projection of what?

Accepted Answer

Hydrogen ion

Answer

Helium

Answer

Oxygen

Answer

None of the above

Question 3

Which of the following compounds is luminous?

Accepted Answer

Porphyrin

Answer

Zymogen

Answer

Chromatin

Answer

Albumin

Question 4

Who invented Polymerase Chain Reaction (PCR)?

Accepted Answer

Kary Mullis

Answer

Alec Jeffreys

Answer

Cesar Milstein

Answer

Gall and Pardue

Question 5

Introduction of DNA into cells with the help of electricity is known as?

Accepted Answer

Electroporation

Answer

Electrotransfer

Answer

Electrofusion

Answer

Electrolysis

Question 6

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 7

The number of gram equivalents in 1 litre of a solution is known as:

Accepted Answer

Normality

Answer

Molarity

Answer

Molality

Answer

None of the above

Question 8

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 9

Electrophoresis done under pH gradient is called?

Accepted Answer

Isoelectric

Answer

Isoosmotic

Answer

Ion exchange

Answer

None of the above

Question 10

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

Biochemical Techniques — MCQs

Biochemical Techniques — MCQs

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