Biochemical Techniques — MCQs

A 45-year-old male patient presents to the emergency department with severe pain and swelling in the big toe joint. He has a history of recurrent joint pain and dietary indiscretion. A specimen from the affected joint is subjected to a test that produces a purple color reaction. What is the test being performed?

Q250

Shadow casting is used in -

Biochemical Techniques Indian Medical PG Practice Questions and MCQs

Question 241: FeCl3 test is used in detection of:

A. Alcohol
B. Acetic acid
C. Phenol (Correct Answer)
D. Hydrochloric acid

Explanation: ***Phenol*** - The ferric chloride (FeCl3) test is used to detect the presence of **phenolic hydroxyl groups** in a compound. - Phenols react with iron(III) ions to form distinctive **colored complexes** (often violet, blue, or green), indicating their presence. *Alcohol* - Alcohols typically do not react with **ferric chloride** to produce a color change. - While some alcohols can be oxidized, the FeCl3 test is not a standard diagnostic tool for alcohols. *Acetic acid* - **Carboxylic acids** like acetic acid do not react with ferric chloride in a way that produces a characteristic color change for identification. - Other tests are used to identify carboxylic acids, such as their **acidity** or reaction with bicarbonates. *Hydrochloric acid* - Hydrochloric acid is a **strong inorganic acid** and does not contain phenolic groups. - It does not react with **ferric chloride** to give a color change that would be used for its diagnosis or identification in this context.

Question 242: Which of the following is a primarily RNA based technique?

A. Western blotting
B. Northern blotting (Correct Answer)
C. Southern blotting
D. Sanger's technique

Explanation: ***Northern blotting*** - **Northern blotting** is a molecular biology technique used to study **gene expression** by detecting specific **RNA molecules** (mRNA) in a sample. - It involves separating RNA fragments by **gel electrophoresis**, transferring them to a membrane, and then detecting specific sequences using **labeled probes**. *Western blotting* - **Western blotting** is a technique used to detect specific **proteins** in a sample. - It involves separating proteins by **gel electrophoresis**, transferring them to a membrane, and then detecting specific proteins using labeled **antibodies**. *Southern blotting* - **Southern blotting** is a molecular biology method used for the detection of **specific DNA sequences** in DNA samples. - It involves separating **DNA fragments** by **gel electrophoresis**, transferring them to a membrane, and then hybridizing with a labeled probe. *Sanger's technique* - **Sanger sequencing**, or the **dideoxy chain-termination method**, is a widely used method for **DNA sequencing**. - It uses **dideoxynucleotides** to terminate DNA synthesis at specific bases, allowing the determination of the **DNA sequence**.

Question 243: What is the primary enzyme commonly used in the polymerase chain reaction (PCR) process?

A. RNA polymerase
B. Topoisomerase
C. DNA polymerase
D. Taq polymerase (Correct Answer)

Explanation: ***Taq polymerase*** - This **heat-stable DNA polymerase**, isolated from *Thermus aquaticus*, is the cornerstone of PCR due to its ability to withstand the high temperatures required for DNA denaturation without losing activity. - Its high processivity and thermal stability allow for multiple rounds of DNA amplification, making it ideal for the **thermostable cycles** of PCR. *RNA polymerase* - **RNA polymerase** is primarily involved in **transcription**, synthesizing RNA from a DNA template in gene expression, not DNA amplification. - It lacks the ability to synthesize DNA from a DNA template, which is the core function required for PCR. *Topoisomerase* - **Topoisomerase** enzymes are involved in managing **DNA supercoiling** during replication and transcription by cutting and rejoining DNA strands. - They do not possess the template-dependent DNA synthesis activity necessary for PCR. *DNA polymerase* - While **DNA polymerase** is responsible for DNA synthesis in general (e.g., in DNA replication), typical eukaryotic or prokaryotic DNA polymerases are **heat-labile** and would be denatured during the high-temperature steps of PCR. - The specific requirement for PCR is a **thermostable DNA polymerase**, which is why *Taq* polymerase (a type of DNA polymerase) is preferred.

Question 244: Which technique is most appropriate for separating proteins based on their molecular weight?

A. SDS-PAGE (Correct Answer)
B. Ion exchange chromatography
C. Affinity chromatography
D. Gel filtration chromatography

Explanation: ***SDS-PAGE*** - **SDS-PAGE (Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis)** denatures proteins and coats them with a uniform negative charge, allowing separation solely based on their **molecular weight**. - Proteins migrate through a polyacrylamide gel matrix, with smaller proteins moving faster and further through the gel. *Ion exchange chromatography* - Separates proteins based on their **net surface charge**, not molecular weight. - Proteins bind to a charged resin and are eluted by changing the salt concentration or pH. *Affinity chromatography* - Separates proteins based on **specific reversible binding interactions** between the protein and a ligand immobilized on a stationary phase. - It exploits biological interactions (e.g., antibody-antigen, enzyme-substrate) rather than physical properties like molecular weight. *Gel filtration chromatography* - Also known as **size exclusion chromatography**, this technique separates proteins based on their **hydrodynamic radius** (their size in solution), not strictly molecular weight in a denatured state. - Larger molecules elute first as they cannot enter the pores of the stationary phase, while smaller molecules are retained longer.

Question 245: In the human body, trichloroethylene (trilene) is primarily metabolized by which process?

A. Enzymatic Oxidation (Correct Answer)
B. Thermal Degradation
C. Photodegradation
D. Chemical Hydrolysis

Explanation: ***Enzymatic Oxidation*** - Trichloroethylene (TCE) is primarily metabolized in the human body through **enzymatic oxidation** by hepatic **cytochrome P450 enzymes**, particularly **CYP2E1** - The oxidative pathway converts TCE to reactive intermediates including **chloral hydrate**, which is further metabolized to **trichloroethanol** and **trichloroacetic acid** - A minor pathway involves **glutathione conjugation**, forming reactive metabolites that contribute to nephrotoxicity - This enzymatic oxidation is the principal metabolic pathway in humans and is responsible for both detoxification and generation of toxic metabolites *Thermal Degradation* - Thermal degradation refers to breakdown of compounds at **high temperatures**, which is an industrial or environmental process - This is not a physiological metabolic pathway in the human body, where temperatures remain constant at 37°C - This process is relevant for TCE disposal or industrial accidents, not human metabolism *Photodegradation* - Photodegradation involves breakdown by **light energy (UV radiation)** and occurs in environmental settings like the atmosphere - The human body does not use photodegradation as a metabolic pathway - Internal organs where TCE metabolism occurs (liver, kidneys) are not exposed to UV light *Chemical Hydrolysis* - Chemical hydrolysis is a non-enzymatic reaction with water that can occur with some compounds - While TCE can undergo limited hydrolysis to form **dichloroacetic acid**, this is a **minor pathway** compared to enzymatic oxidation - The predominant metabolic route for TCE in humans is enzymatic, not simple chemical hydrolysis

Question 246: Which of the following techniques does not determine the structure of proteins?

A. Edman's Sequencing
B. X-ray crystallography
C. Optical rotatory dispersion
D. Spectrophotometry (Correct Answer)

Explanation: ***Spectrophotometry*** - **Spectrophotometry** quantifies the **concentration of a substance** by measuring its absorbance or transmittance of light at specific wavelengths. - While it can identify the presence and quantity of proteins (e.g., using Bradford assay, Lowry method), it does **not provide information** about their **three-dimensional structure**, **amino acid sequence**, or **conformational details**. - It is purely a **quantitative technique**, not a **structural determination method**. *Edman's Sequencing* - **Edman degradation** is a chemical method used to determine the **amino acid sequence** of a protein from its N-terminus. - This technique directly reveals the **primary structure** of a protein (the linear sequence of amino acids), which is fundamental to understanding its overall structure. *X-ray crystallography* - **X-ray crystallography** is the gold standard technique to determine the **three-dimensional structure** of proteins at **atomic resolution**. - It involves crystallizing the protein and analyzing the **diffraction pattern** created when X-rays pass through the crystal, revealing precise spatial arrangements of atoms. *Optical rotatory dispersion* - **Optical rotatory dispersion (ORD)** measures the change in optical rotation of polarized light as a function of wavelength, which is sensitive to the **chiral environment** of molecules. - It is used to study the **secondary structure** (e.g., alpha-helices, beta-sheets) and **conformational changes** in proteins, providing structural information.

Question 247: Which method is used to separate DNA fragments?

A. Ultracentrifugation
B. Agarose gel electrophoresis (Correct Answer)
C. Paper chromatography
D. High pressure liquid chromatography

Explanation: ***Agarose gel electrophoresis*** - This method separates **DNA molecules** based on their **size** and **charge** as they migrate through a gel matrix in an electric field. - Smaller DNA fragments move faster and further through the gel pores than larger ones. *Ultracentrifugation* - This technique separates molecules based on their **density** and **sedimentation rate** in a high-speed centrifuge. - While it can separate DNA from other cellular components, it is not the primary method for separating different sized DNA fragments. *Paper chromatography* - This method separates components of a mixture based on their differential distribution between a **stationary phase (paper)** and a **mobile phase (solvent)**. - It is typically used for separating small molecules like amino acids or pigments, not large DNA fragments. *High pressure liquid chromatography* - **HPLC** is a powerful analytical technique used to separate, identify, and quantify each component in a mixture. - It is used for separating and purifying a wide range of molecules, including proteins and small organic compounds, but it is not commonly used for routine separation of DNA fragments by size.

Question 248: Stain used for tubulin is

A. Luna stain (used for eosinophils)
B. Cajal stain (used for nerve cells)
C. SiR stain (used for tubulin) (Correct Answer)
D. Masson's trichrome (used for connective tissue)

Explanation: ***SiR stain (used for tubulin)*** - **SiR-tubulin** is a live-cell dye that specifically labels **microtubules**, which are polymers of tubulin. - It allows for **super-resolution imaging** of tubulin structures without genetic manipulation. *Luna stain (used for eosinophils)* - **Luna stain** is used to identify **eosinophils** in tissue sections, often in conditions like **eosinophilic esophagitis**. - It specifically stains the **cytoplasmic granules** of eosinophils, not tubulin. *Cajal stain (used for nerve cells)* - **Cajal stain** (e.g., gold chloride sublimate method) is a classical histological technique used to impregnate and visualize **dendritic spines** and **neuronal morphology** in nerve cells. - It focuses on the visualization of neurons and their processes, not microtubule proteins. *Masson's trichrome (used for connective tissue)* - **Masson's trichrome** is a differential stain used to visualize **collagen fibers** (blue or green), **muscle fibers** (red), and **nuclei** (dark brown to black) in tissue sections. - It is primarily used for assessing fibrosis and connective tissue, not specifically for tubulin.

Question 249: A 45-year-old male patient presents to the emergency department with severe pain and swelling in the big toe joint. He has a history of recurrent joint pain and dietary indiscretion. A specimen from the affected joint is subjected to a test that produces a purple color reaction. What is the test being performed?

A. Florence test for choline compounds
B. Teichmann test for blood
C. Acid phosphatase test for prostate
D. Murexide test for uric acid detection (Correct Answer)

Explanation: ***Murexide test for uric acid detection*** - The patient's presentation with **severe pain and swelling in the big toe**, recurrent joint pain, and dietary indiscretion is highly suggestive of **gout**, which is caused by the accumulation of **uric acid crystals**. - The **Murexide test** is a specific qualitative chemical test used to detect the presence of **uric acid** and its derivatives, yielding a characteristic **purple** color in the presence of uric acid. *Florence test for choline compounds* - The **Florence test** is used to identify **choline compounds**, primarily in forensic science for detecting **spermatozoa** by reacting with choline to form dark brown or black crystals. - While it involves a chemical reaction, its application and the compounds it detects are unrelated to the diagnosis of **gout** or uric acid. *Teichmann test for blood* - The **Teichmann test** (hemin test) is a microscopic chemical test used to confirm the presence of **blood** by detecting **hemin crystals**. - This test is not used for diagnosing joint conditions like gout or identifying **uric acid**. *Acid phosphatase test for prostate* - The **acid phosphatase test** measures the level of **acid phosphatase**, an enzyme mainly found in the **prostate gland**, and is used as a marker for **prostate cancer** or other prostatic conditions. - This test is entirely unrelated to the diagnosis of **gout** or the detection of **uric acid** in synovial fluid.

Question 250: Shadow casting is used in -

A. Light microscopy
B. Electron microscopy (Correct Answer)
C. Fluorescence microscopy
D. Phase contrast microscopy

Explanation: ***Electron microscopy*** - **Shadow casting** is a technique used in **electron microscopy** to enhance contrast and reveal the three-dimensional topography of small structures and molecules by depositing a thin film of heavy metal at an angle. - This process creates areas with more metal (which appears darker) and areas shielded from the metal deposition (appearing lighter, like a shadow), thereby outlining the specimen. *Light microscopy* - **Light microscopy** uses visible light to illuminate specimens and a system of lenses to magnify images, and it does not typically employ shadow casting techniques for contrast enhancement. - While various techniques like staining are used for contrast, the principle of creating shadows by metal deposition is not applicable to light interactions with the sample. *Fluorescence microscopy* - **Fluorescence microscopy** utilizes the property of some substances to emit light of a longer wavelength when excited by light of a shorter wavelength (fluorescence), and it relies on fluorochromes for visualization, not shadow casting. - This technique creates contrast based on specific labels or autofluorescence, highlighting particular structures without direct shadowing. *Phase contrast microscopy* - **Phase contrast microscopy** converts phase shifts in light passing through a transparent specimen into changes in amplitude (brightness), which are then visible as differences in image contrast, and it does not involve metal deposition or shadow casting. - This method is particularly useful for observing live, unstained biological samples by detecting optical path differences.

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