Biochemical Techniques Practice Questions

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

SDS-PAGE. ***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.

Q: Which method is used to separate DNA fragments?

Agarose gel electrophoresis. ***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.

Q: Stain used for tubulin is

SiR stain (used for tubulin). ***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.

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

Spectrophotometry. ***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.

Q: 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?

Murexide test for uric acid detection. ***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.

Q: Which of the following acids is MOST commonly used as a reagent in medical laboratory analytical procedures?

Sulphuric acid is used in various laboratory processes.. ***Sulphuric acid*** is the most commonly used acid in medical laboratory analytical procedures. - **Sulfuric acid (H₂SO₄)** is a strong mineral acid with the **widest range of applications** in clinical and research laboratories - Used extensively as a **catalyst and reagent** in numerous analytical procedures including **protein digestion**, **Kjeldahl nitrogen estimation**, and **enzymatic assays** - Essential in **sample preparation** for heavy metal analysis and trace element detection - Utilized in **deproteinization** procedures and various **colorimetric assays** - Its strong **dehydrating properties** make it valuable in multiple biochemical protocols *Nitric acid* - **Nitric acid (HNO₃)** is primarily used for **acid digestion** of samples in trace element analysis - Strong **oxidizing agent** but has more **specialized applications** compared to sulfuric acid - More commonly used in **environmental and toxicology testing** than routine clinical biochemistry - Its highly **corrosive and oxidizing nature** limits its use in routine procedures *Carbolic acid* - **Carbolic acid (phenol/C₆H₅OH)** is technically not a mineral acid but a weak organic acid - Historically used as an **antiseptic and disinfectant** (Lister's antiseptic) - Modern laboratory use is **limited** to specific applications like **phenol-chloroform extraction** in molecular biology - Due to **toxicity concerns**, largely replaced by safer alternatives in routine disinfection *Oxalic acid* - **Oxalic acid (C₂H₂O₄)** is an organic dicarboxylic acid with **specialized applications** - Used in **decalcification of bone samples** for histopathology - Functions as a **reducing agent** in specific analytical procedures - Not a routine reagent in general medical laboratory practice compared to sulfuric acid

Q: What type of radiation is primarily investigated using spectroscopy?

Electromagnetic radiation. ***Electromagnetic radiation*** - **Spectroscopy** is the study of the interaction between matter and **electromagnetic radiation**, covering a wide range from radio waves to gamma rays. - Different forms of **spectroscopy** (e.g., UV-Vis, IR, NMR) analyze how atoms and molecules absorb or emit specific wavelengths of electromagnetic radiation. *Subatomic particles* - While subatomic particles like electrons and protons can be studied using techniques like **mass spectrometry** or **particle detectors**, these are not forms of conventional **spectroscopy**. - **Spectroscopy** primarily focuses on the energy transitions within atoms and molecules induced by electromagnetic waves, not the direct observation of subatomic particle interactions. *Alpha radiation* - **Alpha radiation** consists of **helium nuclei** and is a type of **particulate radiation**, not electromagnetic radiation. - Its study typically involves **particle detectors** to measure its energy and trajectory, rather than spectroscopic methods. *Beta radiation* - **Beta radiation** consists of **high-energy electrons or positrons** and is also a form of **particulate radiation**. - Similar to alpha radiation, its detection and analysis rely on techniques designed for charged particles, not the direct interaction with electromagnetic fields as measured in spectroscopy.

Q: Which method is used to separate a mixture of lipids?

Chromatography. ***Chromatography*** - **Chromatography** (e.g., thin-layer chromatography, gas chromatography, high-performance liquid chromatography) is widely used to separate lipids based on differences in their **polarity**, **molecular weight**, or **solubility** in various solvents. - This method allows for the isolation and identification of different lipid classes and individual lipid species from a complex mixture. *Electrophoresis* - **Electrophoresis** separates molecules based on their **charge** and **size** in an electric field, making it more commonly used for proteins and nucleic acids. - Lipids are generally **uncharged** or have very low charge, which makes them poorly suited for separation by standard electrophoretic methods without modification. *Isoelectric focusing* - **Isoelectric focusing** is a type of electrophoresis that separates molecules based on their **isoelectric point (pI)**, which is the pH at which a molecule has no net charge. - This technique is primarily used for **proteins** and **peptides**, as lipids typically lack ionizable groups necessary for establishing a distinct pI. *PAGE* - **PAGE** (Polyacrylamide Gel Electrophoresis) is a common method used to separate **proteins** and **nucleic acids** based on their size and charge. - Lipids are **hydrophobic** and do not readily migrate through an aqueous polyacrylamide gel matrix, making PAGE unsuitable for their direct separation.

Q: Ninhydrin test is used for?

Amino acids. ***Amino acids*** - The **ninhydrin test** is a chemical test used to detect the presence of **amino acids** and primary and secondary amines. - It produces a **purple-blue color** when it reacts with most amino acids, due to the formation of a colored complex called Ruhemann's purple. *Bile salts* - The detection of **bile salts** typically involves tests like Hay's test or Pettenkofer's test, which are distinct from the ninhydrin reaction. - These tests rely on the physical or chemical properties of bile salts, such as changes in surface tension or specific color reactions with sulfuric acid. *Nucleic acid* - **Nucleic acids** (DNA and RNA) are detected using specific tests like the **diphenylamine test** (for DNA) or orcinol test (for RNA). - These tests target the deoxyribose or ribose sugars present in their structures and result in different color changes compared to ninhydrin. *Lipids* - **Lipids** are typically identified using tests that exploit their nonpolar nature, such as the **emulsion test** or solubility tests in organic solvents. - Their detection does not involve ninhydrin, as they lack the primary or secondary amine groups that react with this reagent.

Q: Which technique is used for the separation of proteins based on their mass?

SDS-PAGE. ***Correct Option: SDS-PAGE*** - **SDS-PAGE (Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis)** separates **denatured proteins** almost exclusively by their **molecular mass**. - **SDS** binds to proteins, imparting a uniform negative charge-to-mass ratio, ensuring that separation is primarily based on their size as they migrate through a **polyacrylamide gel**. - This is the gold standard technique for analyzing proteins by molecular weight. *Incorrect Option: Electrophoresis* - This is a general technique that uses an **electric field** to separate molecules based on their **charge** and **size**. - While it can separate proteins, it doesn't exclusively rely on **mass** without additional modifications (like SDS). - Native electrophoresis separates by charge-to-mass ratio, not mass alone. *Incorrect Option: Salting out* - This technique separates proteins based on their **solubility** in high salt concentrations. - Proteins "salt out" or precipitate at different salt concentrations, which is not directly related to their **mass**. - Based on protein surface properties and hydrophobicity. *Incorrect Option: Ion exchange chromatography* - This method separates proteins based on their **net charge** at a particular pH. - Proteins bind to a charged resin and are eluted by changing the **ionic strength** or **pH** of the buffer. - Two types: cation exchange (negative resin) and anion exchange (positive resin).

Question 1

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

Accepted Answer

SDS-PAGE

Answer

Ion exchange chromatography

Answer

Affinity chromatography

Answer

Gel filtration chromatography

Question 2

Which method is used to separate DNA fragments?

Accepted Answer

Agarose gel electrophoresis

Answer

Ultracentrifugation

Answer

Paper chromatography

Answer

High pressure liquid chromatography

Question 3

Stain used for tubulin is

Accepted Answer

SiR stain (used for tubulin)

Answer

Luna stain (used for eosinophils)

Answer

Cajal stain (used for nerve cells)

Answer

Masson's trichrome (used for connective tissue)

Question 4

Which of the following techniques does not determine the structure of proteins?

Accepted Answer

Spectrophotometry

Answer

Edman's Sequencing

Answer

X-ray crystallography

Answer

Optical rotatory dispersion

Question 5

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?

Accepted Answer

Murexide test for uric acid detection

Answer

Florence test for choline compounds

Answer

Teichmann test for blood

Answer

Acid phosphatase test for prostate

Question 6

Which of the following acids is MOST commonly used as a reagent in medical laboratory analytical procedures?

Accepted Answer

Sulphuric acid is used in various laboratory processes.

Answer

Nitric acid is used in chemical analysis.

Answer

Carbolic acid is used as a disinfectant.

Answer

Oxalic acid is used in various laboratory applications.

Question 7

What type of radiation is primarily investigated using spectroscopy?

Accepted Answer

Electromagnetic radiation

Answer

Subatomic particles

Answer

Alpha radiation

Answer

Beta radiation

Question 8

Which method is used to separate a mixture of lipids?

Accepted Answer

Chromatography

Answer

Electrophoresis

Answer

Isoelectric focusing

Answer

PAGE

Question 9

Ninhydrin test is used for?

Accepted Answer

Amino acids

Answer

Bile salts

Answer

Nucleic acid

Answer

Lipids

Question 10

Which technique is used for the separation of proteins based on their mass?

Accepted Answer

SDS-PAGE

Answer

Electrophoresis

Answer

Salting out

Answer

Ion exchange chromatography

Biochemical Techniques — MCQs

Biochemical Techniques — MCQs

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