Biochemical Techniques Practice Questions

Q: Molecular size of proteins is assessed by which of the following methods?

Absorption mass spectroscopy. ### Explanation **Correct Option: B. Absorption Mass Spectroscopy** Mass Spectrometry (MS) is the gold standard for determining the **molecular weight (size)** and structural composition of proteins. It works by ionizing chemical species and sorting the ions based on their **mass-to-charge (m/z) ratio**. Techniques like MALDI-TOF (Matrix-Assisted Laser Desorption/Ionization - Time of Flight) are specifically designed to measure the mass of large biomolecules like proteins with extreme precision. **Analysis of Incorrect Options:** * **A. Sedimentation:** While ultracentrifugation can provide an estimate of molecular weight via the Svedberg unit (sedimentation coefficient), it primarily measures the rate at which particles settle. It is more commonly used for separating organelles or determining the density of lipoproteins rather than precise molecular sizing of individual proteins. * **C. Lyophilization:** Also known as freeze-drying, this is a **preservation technique**. It removes water from a protein sample to increase its shelf life and stability; it is not an analytical method for size assessment. * **D. Salting Out:** This is a **purification technique** based on solubility. By adding high concentrations of salts (like ammonium sulfate), proteins precipitate out of solution. It does not provide information regarding the molecular size. **High-Yield Clinical Pearls for NEET-PG:** * **SDS-PAGE:** Another common method to estimate protein molecular weight based on electrophoretic mobility. * **Gel Filtration Chromatography:** Also known as Size-Exclusion Chromatography; it separates proteins based on size (larger proteins elute first). * **Proteomics:** Mass Spectrometry is the cornerstone of proteomics, used in clinical settings for identifying bacterial strains (MALDI-TOF) and detecting metabolic disorders in newborns (Tandem MS).

Q: Which process is used to separate fragments of DNA?

Gel electrophoresis. **Explanation:** **Gel Electrophoresis** is the gold-standard technique for separating DNA fragments based on their **size and charge**. DNA molecules are negatively charged (due to the phosphate backbone); when placed in an electric field, they migrate toward the positive electrode (anode). The gel matrix (usually agarose for DNA) acts as a molecular sieve: smaller fragments move faster and further through the pores, while larger fragments move more slowly. **Analysis of Incorrect Options:** * **Paper Chromatography (B):** Primarily used to separate small polar molecules like amino acids or sugars based on their solubility in a stationary vs. mobile phase. * **High-speed Centrifugation (C):** Separates particles based on density and sedimentation rate (e.g., separating organelles or proteins). While "Density Gradient Centrifugation" can separate DNA by density (CsCl gradient), it is not the standard method for separating fragments by length. * **Thin-layer Chromatography (D):** Used for rapid analysis of non-volatile mixtures, such as lipids or drugs, based on adsorption. **High-Yield Facts for NEET-PG:** * **Agarose Gel:** Used for larger DNA fragments (50 bp to several Mb). * **Polyacrylamide Gel (PAGE):** Used for smaller DNA fragments or proteins due to its higher resolving power. * **Visualization:** DNA bands are typically visualized using **Ethidium Bromide (EtBr)**, which fluoresces orange under UV light. * **Pulsed-Field Gel Electrophoresis (PFGE):** A specialized variation used to separate exceptionally large genomic DNA fragments (e.g., for bacterial typing).

Q: Flow cytometry analysis is performed for which of the following estimations?

CD4/CD8 estimation in AIDS. **Explanation:** **Flow Cytometry** is a sophisticated laser-based technology used to analyze the physical and chemical characteristics of particles (usually cells) as they flow in a fluid stream through a beam of light. **Why Option C is Correct:** The primary clinical application of flow cytometry is **Immunophenotyping**. In patients with HIV/AIDS, specific surface markers (Clusters of Differentiation) are identified using fluorescent-labeled monoclonal antibodies. Flow cytometry measures the fluorescence intensity to quantify the absolute counts and ratios of **CD4+ (T-helper cells)** and **CD8+ (T-cytotoxic cells)**. This is the gold standard for monitoring disease progression and the efficacy of Antiretroviral Therapy (ART). **Why Other Options are Incorrect:** * **A. Blood glucose estimation:** Typically performed using enzymatic methods like the **Glucose Oxidase-Peroxidase (GOD-POD)** method or hexokinase method. * **B. Separation of proteins:** Achieved through **Electrophoresis** (based on charge/size) or **Chromatography**. * **D. Estimation of LDL:** Calculated using the **Friedewald formula** [LDL = Total Cholesterol – (HDL + VLDL)] or measured via direct homogeneous assays. **High-Yield Clinical Pearls for NEET-PG:** * **Principle:** Flow cytometry works on the principles of **Light Scattering** (Forward scatter for size; Side scatter for granularity/complexity) and **Fluorescence**. * **Other Applications:** Diagnosis of leukemias/lymphomas, DNA ploidy analysis, and detecting **PNH (Paroxysmal Nocturnal Hemoglobinuria)** by looking for the absence of CD55 and CD59. * **FACS:** Fluorescence-Activated Cell Sorting is a specialized type of flow cytometry that not only analyzes but also physically sorts cells into different containers.

Q: What is the principle of the Benedict's test for urine reducing substances?

Cu2+ ions are reduced to Cu+ ions by enediols. ### Explanation **1. Why Option A is Correct:** Benedict’s test is a semi-quantitative test used to detect **reducing sugars** (like glucose, fructose, and galactose) in urine. In an alkaline medium, reducing sugars undergo tautomerization to form highly reactive **enediols**. These enediols act as reducing agents; they donate electrons to the **cupric ions (Cu²⁺)** present in the Benedict’s reagent (as copper sulfate), reducing them to **cuprous ions (Cu⁺)**. These cuprous ions then react with hydroxyl ions to form cuprous hydroxide, which upon heating yields a **cuprous oxide (Cu₂O) precipitate**. The color change (from blue to green, yellow, orange, or brick red) depends on the concentration of the reducing sugar. **2. Why Other Options are Incorrect:** * **Option B:** This is the reverse of the actual reaction. Oxidation involves losing electrons, whereas the copper ions must *gain* electrons (reduction) to form the precipitate. * **Options C & D:** Benedict’s reagent specifically utilizes **Copper (Cu)**, not Iron (Fe). Iron-based redox reactions are characteristic of other biochemical processes (like the Fenton reaction or Cytochrome chain), but not standard urine sugar testing. **3. Clinical Pearls for NEET-PG:** * **Specificity:** Benedict’s test is **not specific for glucose**. It gives positive results for other reducing sugars (lactose in pregnancy, fructose in Essential Fructosuria, galactose in Galactosemia) and non-sugar reducers (Vitamin C, Uric acid, Salicylates). * **Glucose Specificity:** To confirm if a positive Benedict’s test is specifically due to glucose, the **Glucose Oxidase method (Dipstick)** is used. * **Composition:** Benedict’s reagent contains **Copper sulfate** (provides Cu²⁺), **Sodium carbonate** (provides alkaline medium), and **Sodium citrate** (prevents spontaneous precipitation of Cu(OH)₂ by acting as a chelating agent).

Q: Sodium fluoride is added to:

Prevent glycolysis. **Explanation:** **1. Why Option A is Correct:** Sodium fluoride (NaF) is the agent of choice for blood glucose estimation because it acts as a potent **glycolytic inhibitor**. It works by inhibiting the enzyme **Enolase** in the glycolytic pathway. Specifically, fluoride ions bind with magnesium and phosphate to form a magnesium-fluorophosphate complex, which competes with the substrate for the active site of Enolase. By blocking this step (the conversion of 2-phosphoglycerate to phosphoenolpyruvate), NaF prevents the breakdown of glucose by RBCs and WBCs *in vitro*, ensuring the measured glucose level reflects the patient's actual blood sugar at the time of collection. **2. Why Other Options are Incorrect:** * **Option B (Glycogenolysis):** While NaF inhibits glycolysis, its primary clinical utility in a vacutainer is preventing the metabolic consumption of free glucose. Glycogenolysis (breakdown of glycogen) occurs primarily in the liver and muscle; in a blood sample, the immediate concern is the rapid consumption of existing glucose by glycolysis. * **Option C (Coagulation):** Sodium fluoride has very weak anticoagulant properties. Therefore, it is almost always combined with **Potassium Oxalate**, which acts as the actual anticoagulant by precipitating calcium ions. **3. High-Yield Clinical Pearls for NEET-PG:** * **The Grey Top Vacutainer:** Contains Sodium Fluoride (antiglycolytic) and Potassium Oxalate (anticoagulant) in a **1:3 ratio**. * **Rate of Glycolysis:** At room temperature, blood glucose levels decrease by approximately **5–10 mg/dL per hour** if an inhibitor is not used. * **Enzyme Inhibition:** Remember that fluoride inhibition of Enolase is **reversible** and requires magnesium as a cofactor for the complex to form. * **Interference:** High concentrations of fluoride can inhibit other enzymes like urease; thus, fluoride tubes should not be used for urea estimation using urease methods.

Q: Mutations that completely disrupt the function of a gene are used in which of the following techniques?

Targeted gene disruption. **Explanation:** **Targeted gene disruption**, commonly known as **Gene Knockout**, is the correct answer. This technique involves the deliberate "silencing" or inactivation of a specific gene to study its function. By using homologous recombination to replace a functional gene with an inactive or mutated DNA sequence, researchers can observe the resulting phenotypic changes. This allows for the determination of the gene's physiological role and the creation of animal models for human genetic diseases. **Analysis of Incorrect Options:** * **Non-sense mutation (A):** This is a type of point mutation where a codon is changed to a premature stop codon (UAG, UAA, UGA). While it disrupts gene function, it is a *type* of mutation, not a laboratory *technique* used to study gene function. * **Restriction Fragment Length Polymorphism (RFLP) (B):** This is a technique used to detect variations in DNA sequences (polymorphisms) based on different patterns of DNA fragments after digestion with restriction enzymes. It is used for mapping and diagnosis, not for disrupting gene function. * **Knock-in (D):** This technique involves inserting a functional gene (often a mutated version or a reporter gene) into a specific locus. Unlike a knockout, which aims to eliminate function, a knock-in aims to replace or add a specific function. **High-Yield Clinical Pearls for NEET-PG:** * **Knockout Mice:** The most common model for studying Mendelian disorders. * **CRISPR-Cas9:** The modern, most efficient tool for targeted gene disruption and editing. * **RNA Interference (RNAi):** Often confused with knockout; RNAi causes gene "knockdown" (temporary/partial suppression) rather than permanent disruption at the DNA level.

Q: Restriction fragment length polymorphism uses which of the following techniques?

Southern blotting. ### Explanation **1. Why Southern Blotting is Correct:** Restriction Fragment Length Polymorphism (RFLP) is a technique used to detect variations in homologous DNA sequences. The process involves: * **Digestion:** DNA is cut into fragments using **Restriction Endonucleases**. * **Separation:** Fragments are separated by size via gel electrophoresis. * **Southern Blotting:** The DNA fragments are transferred from the gel to a membrane and hybridized with a labeled **DNA probe**. Since RFLP specifically analyzes **DNA** variations, Southern blotting (the gold standard for DNA detection) is the integral technique used to visualize these fragments. **2. Why Other Options are Incorrect:** * **Northern Blotting:** This technique is used for the detection and quantification of **RNA**. It is used to study gene expression but cannot be used for RFLP as RFLP analyzes genomic DNA. * **Western Blotting:** This is used for the detection of specific **Proteins** using antibodies (e.g., confirmatory test for HIV). * **Eastern Blotting:** This is an extension of western blotting used to detect **post-translational modifications** of proteins (like carbohydrates or lipids). It is not a standard diagnostic tool for genetic polymorphisms. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Mnemonic (SNOW DROP):** * **S**outhern = **D**NA * **N**orthern = **R**NA * **O** = **O** (Nothing) * **W**estern = **P**rotein * **RFLP Applications:** Used in forensic "DNA fingerprinting," paternity testing, and identifying carriers of genetic diseases like Sickle Cell Anemia (where a mutation destroys a restriction site). * **Restriction Endonucleases:** Also known as "molecular scissors," they recognize specific palindromic sequences.

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).

Question 1

The total body radical burden can be estimated by which of the following methods?

Accepted Answer

All of the above

Answer

FOX Assay

Answer

Estimation of Dialdehydes

Answer

Measurement of Pentane and Methane in exhaled air

Question 2

Molecular size of proteins is assessed by which of the following methods?

Accepted Answer

Absorption mass spectroscopy

Answer

Sedimentation

Answer

Lyophilization

Answer

Salting out

Question 3

Which process is used to separate fragments of DNA?

Accepted Answer

Gel electrophoresis

Answer

Paper chromatography

Answer

High-speed centrifugation

Answer

Thin-layer chromatography

Question 4

Flow cytometry analysis is performed for which of the following estimations?

Accepted Answer

CD4/CD8 estimation in AIDS

Answer

Blood glucose estimation

Answer

Separation of proteins

Answer

Estimation of LDL

Question 5

What is the principle of the Benedict's test for urine reducing substances?

Accepted Answer

Cu2+ ions are reduced to Cu+ ions by enediols

Answer

Cu+ ions are oxidized to Cu2+ ions by enediols

Answer

Fe2+ ions are reduced to Fe+ ions by enediols

Answer

Fe+ ions are reoxidized to Fe2+ ions by enediols

Question 6

Which of the following correctly defines the relationship between Quality Assurance (QA), Quality Control (QC), Internal Quality Assurance (IQA), and External Quality Assurance (EQA)?

Accepted Answer

QA = QC + IQA + EQA

Answer

QC = QA + IQA - EQA

Answer

QC = QA + IQA + EQA

Answer

QA = QC + IQA - EQA

Question 7

Sodium fluoride is added to:

Accepted Answer

Prevent glycolysis

Answer

Prevent glucogenolysis

Answer

Prevent coagulation

Answer

All

Question 8

Mutations that completely disrupt the function of a gene are used in which of the following techniques?

Accepted Answer

Targeted gene disruption

Answer

Non-sense mutation

Answer

Restriction fragment length polymorphism

Answer

Knock-in

Question 9

Restriction fragment length polymorphism uses which of the following techniques?

Accepted Answer

Southern blotting

Answer

Northern blotting

Answer

Western blotting

Answer

Eastern blotting

Question 10

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

Biochemical Techniques — MCQs

Biochemical Techniques — MCQs

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