Biochemical Techniques Practice Questions

Q: Which enzyme is considered a marker enzyme of mitochondria?

Glutamic dehydrogenase. **Explanation** Marker enzymes are specific enzymes used to identify and assess the purity of isolated cell organelles during biochemical analysis. **Why Glutamic Dehydrogenase (GDH) is correct:** Glutamic dehydrogenase is a high-yield marker enzyme for the **mitochondrial matrix**. It plays a crucial role in nitrogen metabolism by catalyzing the oxidative deamination of glutamate. While **Succinate Dehydrogenase (SDH)** is the classic marker for the inner mitochondrial membrane, GDH is the definitive marker for the matrix. **Analysis of Incorrect Options:** * **A. Na+ - K+ ATPase:** This is the classic marker enzyme for the **Plasma Membrane**. It maintains the electrochemical gradient across the cell surface. * **C. Lactate Dehydrogenase (LDH):** This is the marker enzyme for the **Cytosol**. It is the terminal enzyme of anaerobic glycolysis. * **D. No specific enzyme:** Incorrect, as almost every organelle has a specific biochemical marker (e.g., Acid phosphatase for Lysosomes, Catalase for Peroxisomes). **High-Yield Clinical Pearls for NEET-PG:** * **Mitochondrial Markers:** * Outer Membrane: Monoamine Oxidase (MAO). * Inner Membrane: Succinate Dehydrogenase (SDH), Cytochrome Oxidase. * Matrix: Glutamic Dehydrogenase (GDH). * **Other Key Markers:** * **Golgi Apparatus:** Galactosyl transferase. * **Endoplasmic Reticulum:** Glucose-6-phosphatase. * **Lysosomes:** Acid phosphatase. * **Nucleus:** DNA Polymerase / RNA Polymerase. * **Clinical Note:** Elevated serum GDH levels can indicate severe liver cell necrosis, as the enzyme is released from the mitochondria into the bloodstream.

Q: Benedict test is used for the detection of which substance in urine?

Reducing sugars. **Explanation:** **1. Why Reducing Sugars is Correct:** The Benedict’s test is a semi-quantitative test used to detect **reducing sugars** (such as glucose, fructose, lactose, and maltose) in the urine. The Benedict’s reagent contains **cupric ions ($Cu^{2+}$)** in an alkaline medium. When heated with a reducing sugar, the free aldehyde or ketone group of the sugar reduces the blue cupric ions to insoluble **cuprous oxide ($Cu_2O$)**, which forms a colored precipitate. The color change (Green → Yellow → Orange → Brick Red) indicates the concentration of sugar present. **2. Why Other Options are Incorrect:** * **Bile Salts:** Detected using **Hay’s Sulphur Test**, which relies on the property of bile salts to lower the surface tension of urine. * **Bile Pigments (Bilirubin):** Detected using **Fouchet’s Test**, where barium chloride and Fouchet’s reagent produce a green/blue color (biliverdin). * **Ketone Bodies:** Detected using **Rothera’s Test**, where sodium nitroprusside reacts with acetone or acetoacetate to form a purple/permanganate-colored ring. **3. Clinical Pearls & High-Yield Facts:** * **Specificity:** Benedict’s test is **not specific for glucose**. It can give positive results for other reducing substances like Vitamin C (Ascorbic acid), salicylates, and uric acid. * **Glucose Specificity:** To specifically detect glucose (and rule out other sugars), the **Dipstick method (Glucose Oxidase method)** is used. * **Inborn Errors of Metabolism:** A positive Benedict’s test with a negative Dipstick test suggests the presence of non-glucose reducing sugars like **galactose** (Galactosemia) or **fructose** (Hereditary Fructose Intolerance). * **Sucrose:** It is a **non-reducing sugar** and will give a negative Benedict’s test unless it is first hydrolyzed into glucose and fructose.

Q: Which of the following methods is MOST sensitive for glucose estimation?

GOD POD method. **Explanation:** The estimation of blood glucose is a fundamental biochemical investigation. The **GOD-POD (Glucose Oxidase-Peroxidase) method** is considered highly sensitive and specific because it utilizes a coupled enzymatic reaction. 1. **Glucose Oxidase (GOD)** specifically oxidizes $\beta$-D-glucose to gluconic acid and hydrogen peroxide ($H_2O_2$). 2. **Peroxidase (POD)** then breaks down $H_2O_2$ to release nascent oxygen, which reacts with a chromogen (like 4-aminophenazone) to form a colored quinoneimine complex. The intensity of the color is directly proportional to the glucose concentration. Its high sensitivity stems from the enzymatic specificity for glucose, minimizing interference from other substances. **Analysis of Incorrect Options:** * **Hexokinase Method:** While this is the **"Reference Method"** (Gold Standard) due to its extreme accuracy and precision, in many clinical laboratory contexts, the GOD-POD method is preferred for routine high-sensitivity screening due to cost-effectiveness and ease of automation. * **O-Toluidine Method:** A condensation method where glucose reacts with aromatic amines in glacial acetic acid. It is specific but uses corrosive reagents and is less sensitive than enzymatic methods. * **Folin-Wu Method:** A classic copper reduction method. It is the **least specific** because it measures all "reducing sugars" and non-sugar reducing substances (like glutathione and uric acid), leading to falsely elevated values. **High-Yield Clinical Pearls for NEET-PG:** * **Specimen Collection:** Use **Fluoride vials** (Grey top). Sodium fluoride inhibits **enolase**, preventing glycolysis, while Potassium Oxalate acts as the anticoagulant. * **Gold Standard:** Hexokinase method. * **Most Specific:** GOD-POD (specifically for $\beta$-D-glucose). * **Renal Threshold for Glucose:** Approximately **180 mg/dL**. When blood glucose exceeds this, glucosuria occurs.

Q: If the optical density is 2, what percentage of light is transmitted?

1%. ### Explanation **Concept and Calculation:** Optical Density (OD), also known as **Absorbance (A)**, is a logarithmic measurement of how much light is absorbed by a solution. It is mathematically defined by the **Beer-Lambert Law** using the formula: $$A = \log_{10} \left(\frac{1}{T}\right) \quad \text{or} \quad A = 2 - \log_{10}(\%T)$$ Where **T** is Transmittance (expressed as a fraction) and **%T** is the percentage of light transmitted. Given **OD = 2**: $$2 = \log_{10} \left(\frac{1}{T}\right)$$ $$10^2 = \frac{1}{T} \implies 100 = \frac{1}{T}$$ $$T = 0.01$$ To find the percentage: $0.01 \times 100 = \mathbf{1\%}$. **Analysis of Options:** * **Option C (1%):** Correct. An OD of 2 means the solution is dense enough to absorb 99% of the incident light, allowing only 1/100th (1%) to pass through. * **Option A (100%):** Incorrect. This occurs when **OD = 0** (no light is absorbed), typical of a "blank" solution. * **Option B (10%):** Incorrect. This corresponds to an **OD of 1** ($\log_{10}(10) = 1$). * **Option D (0.10%):** Incorrect. This corresponds to an **OD of 3** ($\log_{10}(1000) = 3$). **Clinical Pearls for NEET-PG:** 1. **Inverse Relationship:** Absorbance and Transmittance are inversely related; as a solution becomes more concentrated (higher OD), less light is transmitted. 2. **Linearity:** According to Beer’s Law, Absorbance is directly proportional to the concentration of the solute. This is the principle used in clinical chemistry to measure blood glucose, urea, and creatinine. 3. **High-Yield Values:** * OD 0 = 100% Transmission * OD 1 = 10% Transmission * OD 2 = 1% Transmission * OD 3 = 0.1% Transmission

Q: Which of the following is the best technique to screen neonates for inherited metabolic disorders?

Tandem mass spectrometry. **Explanation:** **Tandem Mass Spectrometry (TMS/MS-MS)** is the gold standard for newborn screening (NBS) because of its high sensitivity, specificity, and "multiplexing" capability. Unlike traditional methods, TMS can detect over 30–50 different metabolic disorders (including amino acid disorders, organic acidemias, and fatty acid oxidation defects) from a single dried blood spot in just a few minutes. It works by identifying and quantifying diagnostic metabolites (acylcarnitines and amino acids) based on their mass-to-charge ratio. **Analysis of Incorrect Options:** * **Northern Blotting:** Used specifically for the detection and quantification of **RNA** sequences. It is a research tool and not suitable for rapid, high-throughput clinical screening. * **PCR (Polymerase Chain Reaction):** Used to amplify specific **DNA** sequences. While useful for confirming a genetic diagnosis, it is not the primary screening tool for metabolic metabolites in neonates. * **ChIP (Chromatin Immunoprecipitation) technique:** A method used to investigate the interaction between **proteins and DNA** (e.g., transcription factor binding). It has no role in routine metabolic screening. **High-Yield Clinical Pearls for NEET-PG:** * **Guthrie Test:** The historical "heel prick" test used for Phenylketonuria (PKU) screening; it has largely been replaced by TMS. * **Timing:** Newborn screening is ideally performed **24–48 hours after birth** to allow for the accumulation of metabolites after protein ingestion. * **Commonly Screened Disorders:** PKU, Maple Syrup Urine Disease (MSUD), Galactosemia, Congenital Hypothyroidism, and Congenital Adrenal Hyperplasia (CAH).

Q: Which of the following tests can distinguish between monosaccharides and disaccharides?

Barfoed's test. **Explanation:** **1. Why Barfoed’s Test is Correct:** Barfoed’s test is specifically designed to distinguish **monosaccharides from reducing disaccharides**. The reagent consists of copper acetate in dilute acetic acid (acidic medium). While both monosaccharides and reducing disaccharides can reduce cupric ions to cuprous oxide, **monosaccharides are stronger reducing agents** and react much faster. In an acidic medium, monosaccharides produce a red precipitate within 1–3 minutes, whereas reducing disaccharides require prolonged boiling (7–12 minutes) because they must first undergo slight hydrolysis. **2. Analysis of Incorrect Options:** * **Bial’s Test:** Used to detect **Pentoses** (e.g., ribose). It uses orcinol and HCl to produce a blue-green condensation product. * **Seliwanoff’s test:** Used to distinguish **Ketohexoses** (e.g., fructose) from aldohexoses. It uses resorcinol and HCl to produce a cherry-red complex. * **Hydrolysis test:** This is a general procedure used to break down glycosidic bonds in disaccharides or polysaccharides into their constituent monosaccharides; it is not a specific diagnostic color test for differentiation. **3. High-Yield Clinical Pearls for NEET-PG:** * **Benedict’s vs. Barfoed’s:** Benedict’s test is performed in an **alkaline** medium (detects all reducing sugars), while Barfoed’s is in an **acidic** medium (distinguishes based on the rate of reaction). * **Sucrose:** It is a non-reducing sugar and will give a **negative** result for both Benedict’s and Barfoed’s tests unless hydrolyzed first. * **Osazone Test:** Another method to differentiate sugars based on crystal morphology (e.g., Needle-shaped for Glucosazone, Sunflower-shaped for Maltosazone).

Q: The Biuret reaction is specific for which functional group?

Peptide bonds (-CONH-). **Explanation:** The **Biuret reaction** is a fundamental colorimetric test used for the detection and quantification of proteins. **1. Why Option A is correct:** The test relies on the presence of **peptide bonds (-CONH-)**. In an alkaline medium, cupric ions ($Cu^{2+}$) react with the nitrogen atoms of at least two peptide bonds to form a characteristic **violet or purple-colored coordination complex**. For a positive result, a molecule must contain at least two peptide bonds (i.e., it must be a tripeptide or larger). This is why free amino acids (except histidine) and dipeptides give a negative Biuret test. **2. Why Options B and C are incorrect:** While the Biuret reagent is named after the compound "biuret" (formed by heating urea), the reaction is specifically used in biochemistry to identify the repeating peptide backbone of proteins. * **-CSNH2 (Thiocarbonamide) and -NHNH2 (Hydrazine):** While certain non-protein compounds containing these groups (like oxamide or malonamide) can technically react with copper salts, they are not the physiological targets of this test in a medical biochemistry context. In the scope of the NEET-PG syllabus, the Biuret test is defined by its specificity for the **peptide linkage**. **Clinical Pearls & High-Yield Facts:** * **Minimum Requirement:** A minimum of **two peptide bonds** is required for a positive test. * **Color Intensity:** The intensity of the purple color is directly proportional to the number of peptide bonds present, making it useful for quantitative protein estimation. * **Interference:** High concentrations of ammonium salts can interfere with the reaction. * **Clinical Use:** It is commonly used in laboratories to measure total serum protein levels. * **Note:** Histidine is the only amino acid that may give a positive result due to its imidazole ring.

Question 1

Which enzyme is considered a marker enzyme of mitochondria?

Accepted Answer

Glutamic dehydrogenase

Answer

Na+ - K+ ATPase

Answer

Lactate dehydrogenase

Answer

No specific enzyme

Question 2

Benedict test is used for the detection of which substance in urine?

Accepted Answer

Reducing sugars

Answer

Bile salts

Answer

Bile pigments

Answer

Ketone bodies

Question 3

Atomic absorption Inductively Coupled Plasma Mass Spectroscopy (ICP-MS) is used to measure/detect what?

Accepted Answer

Trace & metal elements

Answer

Hb-derivatives

Answer

Immunoglobulins

Answer

Organic compounds

Question 4

DNA fragments formed by the action of Restriction endonucleases are separated by which technique?

Accepted Answer

Agarose gel electrophoresis

Answer

Gel electrophoresis

Answer

Paper chromatography

Answer

High pressure liquid chromatography

Question 5

Which of the following methods is MOST sensitive for glucose estimation?

Accepted Answer

GOD POD method

Answer

O-Toluidine method

Answer

Folin-Wu method

Answer

Hexokinase method

Question 6

If the optical density is 2, what percentage of light is transmitted?

Accepted Answer

1%

Answer

100%

Answer

10%

Answer

0.10%

Question 7

Which of the following is the best technique to screen neonates for inherited metabolic disorders?

Accepted Answer

Tandem mass spectrometry

Answer

Northern Blotting

Answer

PCR

Answer

ChIP technique

Question 8

Which of the following tests can distinguish between monosaccharides and disaccharides?

Accepted Answer

Barfoed's test

Answer

Bial's Test

Answer

Seliwanoff's test

Answer

Hydrolysis test

Question 9

The Biuret reaction is specific for which functional group?

Accepted Answer

Peptide bonds (-CONH-)

Answer

-CSNH2 group

Answer

-NHNH2 group

Answer

All of the above

Question 10

Which of the following is considered the gold standard for demonstrating human chorionic gonadotropin (hCG)?

Accepted Answer

Radioimmunoassay (RIA)

Answer

Latex agglutination

Answer

Immunofluorescence

Answer

Enzyme-linked immunosorbent assay (ELISA)

Biochemical Techniques — MCQs

Biochemical Techniques — MCQs

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