Biochemical Techniques — MCQs

Biochemical Techniques Indian Medical PG Practice Questions and MCQs

Question 201: Western blot is done for:

A. Protein (Correct Answer)
B. RNA
C. Lipid
D. DNA

Explanation: ***Protein*** - **Western blot** is a laboratory technique used to detect specific **proteins** in a sample of tissue homogenate or extract. - It involves separating proteins by **electrophoresis**, transferring them to a membrane, and then detecting them using **antibodies**. *RNA* - **Northern blot** is the technique specifically designed for the detection and analysis of **RNA** molecules. - It involves separating RNA fragments by **electrophoresis**, transferring them to a membrane, and querying with a labeled probe. *Lipid* - There is no direct "lipid blot" technique analogous to Western, Northern, or Southern blots. - **Lipids** are typically analyzed using techniques such as mass spectrometry, thin-layer chromatography, or gas chromatography. *DNA* - **Southern blot** is the molecular biology method used for the detection of specific **DNA** sequences in DNA samples. - It involves fragmenting DNA, separating by **electrophoresis**, and then hybridizing with a labeled DNA probe.

Question 202: Western blot is used for:

A. RNA
B. Maternal DNA
C. DNA
D. Proteins (Correct Answer)

Explanation: ***Proteins*** - **Western blot** (also known as protein immunoblot) is a widely used analytical technique in molecular biology and immunogenetics to **detect specific proteins** in a given sample. - It involves separating proteins by size using gel electrophoresis, transferring them to a membrane, and then detecting the protein of interest using specific **antibodies**. *RNA* - The technique used to detect RNA is called **Northern blot**, which involves separating RNA fragments by size and then detecting specific RNA sequences using nucleic acid probes. - While both Northern and Western blots involve electrophoresis and transfer to a membrane, the target molecule is different. *Maternal DNA* - Detection of specific DNA sequences, including maternal DNA or fetal DNA, is typically performed using techniques like **Southern blot** or, more commonly now, **PCR-based methods** and **next-generation sequencing**. - Maternal DNA itself is not the specific target of a Western blot; proteins derived from any source of DNA, maternal or otherwise, would be the target. *DNA* - The technique primarily used for the detection of specific DNA sequences is **Southern blot**, which involves separating DNA fragments by size and using labeled probes to identify target sequences. - Western blot is fundamentally designed for protein analysis, relying on antibody-antigen recognition rather than DNA hybridization.

Question 203: Northern blot technique is used in the detection of:

A. Plasmid
B. RNA (Correct Answer)
C. Prion
D. DNA

Explanation: ***RNA*** - The **Northern blot** technique specifically detects and measures **RNA** sequences in a sample - It involves separating RNA fragments by **gel electrophoresis**, transferring them to a membrane, and hybridizing with a **labeled complementary probe** - **Memory aid:** SNoW DRoP - **S**outhern = D**NA**, **No**rthern = **R**NA, **W**estern = **P**rotein *Incorrect: Plasmid* - **Plasmids** are circular **DNA** molecules, not RNA - Their detection uses **agarose gel electrophoresis** with staining, or **Southern blotting** for specific DNA sequence identification - Northern blot is designed specifically for RNA, not DNA-based structures *Incorrect: Prion* - **Prions** are **misfolded proteins** causing neurodegenerative diseases (e.g., Creutzfeldt-Jakob disease) - They are **not nucleic acids** (neither DNA nor RNA) - Detection requires **Western blot** or immunohistochemistry for protein analysis *Incorrect: DNA* - Detection of specific **DNA** sequences uses the **Southern blot** technique - Southern blot employs DNA probes to hybridize with target DNA after gel electrophoresis - Northern blot is exclusively for RNA, not DNA

Question 204: Spectroscopy primarily studies the interaction between _____ and matter.

A. Alpha particles
B. Protons
C. Electromagnetic radiation (Correct Answer)
D. Positrons

Explanation: ***Electromagnetic radiation*** - **Spectroscopy** is the study of the interaction between **matter** and **electromagnetic radiation**, which includes a range from radio waves to gamma rays. - This interaction provides information about the **structure, composition, and physical properties** of matter. *Alpha particles* - **Alpha particles** are composed of two protons and two neutrons, essentially a helium nucleus. - While they interact with matter, their study is more characteristic of **nuclear physics** and **radioactivity**, not the primary focus of spectroscopy. *Protons* - **Protons** are subatomic particles with a positive charge found in the nucleus of an atom. - Their interaction with matter is studied in various fields, but spectroscopy primarily uses **electromagnetic radiation** to probe atomic and molecular energy levels. *Positrons* - **Positrons** are the antimatter counterparts of electrons, having a positive charge. - Their interaction with matter leads to **annihilation events** producing gamma rays, which is fundamental to techniques like Positron Emission Tomography (**PET**), but not the broad field of spectroscopy.

Question 205: Osmotic pressure of 1 mol of ideal solute relative to pure water is:

A. 2 atm.
B. 6.5 atm.
C. 4 atm.
D. 22.4 atm. (Correct Answer)

Explanation: ***22.4 atm.*** - The osmotic pressure (π) is calculated using the formula **π = nRT/V** or **π = CRT**, where C is molar concentration. - For **1 mole of ideal solute in 1 liter** of solution at **standard temperature (273 K, 0°C)**: π = (1 mol × 0.0821 L·atm/mol·K × 273 K) / 1 L = **22.4 atm** - This represents a **colligative property** that depends only on the number of solute particles, not their identity. - Note: The numerical value coincidentally equals the molar volume of an ideal gas at STP (22.4 L), but these are different physical quantities. *2 atm.* - This value is **too low** for 1 molar solution at standard conditions. - This might represent osmotic pressure at much lower concentration or temperature, but doesn't match the calculation for 1 mole/L at STP. *6.5 atm.* - This arbitrary value does **not correspond** to any standard calculation for osmotic pressure. - Using π = CRT with standard values cannot yield this result for a 1 M solution. *4 atm.* - This value is **significantly lower** than the calculated osmotic pressure for 1 mole of ideal solute per liter. - It does not align with the **van't Hoff equation** for osmotic pressure at standard conditions.

Question 206: Substance with same atomic number but different mass number –

A. Isotope (Correct Answer)
B. Mineral
C. Isobar
D. Atom

Explanation: ***Isotope*** - **Isotopes** are atoms of the same element, meaning they have the **same atomic number** (number of protons). - They differ in their **mass number** due to varying numbers of neutrons. *Mineral* - A **mineral** is a naturally occurring solid, inorganic substance with a definite chemical composition and crystal structure. - This definition does not relate to the atomic or mass numbers of individual atoms. *Isobar* - **Isobars** are atoms of different elements that have the **same mass number** but different atomic numbers. - This is the opposite of the given description. *Atom* - An **atom** is the basic unit of a chemical element. - While isotopes are types of atoms, the term "atom" itself is too broad and doesn't specify the relationship described.

Question 207: Which of the following separates proteins solely on the basis of their molecular size?

A. Isoelectric focusing
B. Chromatography on a diethylaminoethyl (DEAE) cellulose column
C. Gel filtration chromatography (Correct Answer)
D. Chromatography on a carboxymethyl (CM) cellulose column

Explanation: ***Gel filtration chromatography*** - Also known as **size-exclusion chromatography**, this method separates proteins based on their **hydrodynamic volume** (molecular size and shape). - Larger proteins pass through the column more quickly because they are excluded from the pores of the stationary phase, while smaller proteins enter the pores and have a longer, more tortuous path. *Isoelectric focusing* - This technique separates proteins based on their **isoelectric point (pI)**, which is the pH at which the protein has no net electrical charge. - Proteins migrate through a pH gradient until they reach the point where their net charge is zero. *Chromatography on a diethylaminoethyl (DEAE) cellulose column* - **DEAE cellulose** is an **anion-exchange resin**, meaning it binds **negatively charged** proteins. - Separation is based on the **net charge** of the protein at a given pH. *Chromatography on a carboxymethyl (CM) cellulose column* - **CM cellulose** is a **cation-exchange resin**, meaning it binds **positively charged** proteins. - Separation is based on the **net charge** of the protein at a given pH.

Question 208: Water is a poor conductor of electricity because it is

A. Neutral solution
B. Dense liquid
C. Non ionised (Correct Answer)
D. Covalently bonded

Explanation: ***Non ionised*** - Pure water is a **covalent compound** and does not dissociate into ions readily. - Electrical conductivity requires the presence of **free-moving ions** to carry charge, which pure water lacks. - This is the **most direct explanation** for poor electrical conductivity. *Neutral solution* - While water is a **neutral solution** (pH 7), its neutrality refers to its balance of H⁺ and OH⁻ ions, not its ability to conduct electricity. - Many neutral solutions, if they contain dissolved ions (e.g., salt water), can be good conductors. *Dense liquid* - The **density of water** (approximately 1 g/mL) has no direct bearing on its electrical conductivity. - Electrical conductivity is determined by the presence and mobility of charge carriers, not mass per unit volume. *Covalently bonded* - While water molecules are indeed **covalently bonded** (electrons shared between oxygen and hydrogen atoms), this describes the **molecular structure** rather than directly explaining conductivity. - The covalent bonding explains **why** water remains non-ionized, but "non-ionised" is the more **direct answer** to the question of electrical conductivity. - Both statements are true, but in the context of electrical conduction, the lack of ions is the immediate cause.

Question 209: Northern blot technique is used in the detection of

A. Protein
B. RNA (Correct Answer)
C. DNA
D. plasmid

Explanation: ***RNA*** - The **Northern blot** is a laboratory technique used to study **gene expression** by detecting specific **RNA molecules** (mRNA, rRNA, or tRNA) in a sample. - It involves separating RNA fragments by size via gel electrophoresis, transferring them to a membrane, and then probing with a labeled nucleic acid sequence complementary to the target RNA. *Protein* - The detection of **proteins** is typically performed using a **Western blot** technique, which identifies specific proteins through antibody binding. - While RNA ultimately codes for proteins, Northern blotting directly analyzes the **RNA transcript** itself, not the protein product. *DNA* - **Southern blot** is the technique specifically designed for the detection of **DNA sequences**, used to analyze genomic DNA or specific DNA fragments. - Northern blot differentiates itself from Southern blot by its application in analyzing **gene expression at the RNA level**. *plasmid* - A **plasmid** is a small, circular, extrachromosomal **DNA molecule** found in bacteria and some other organisms. - Detection of plasmids, being DNA, would primarily involve techniques like **Southern blot** or **PCR**, not Northern blot which targets RNA.

Question 210: Protein Electrophoresis (PE) is a type of:-

A. Chromatographic technique
B. Immunological technique
C. Electrophoretic technique (Correct Answer)
D. Spectroscopic technique

Explanation: ***Electrophoretic technique*** - **Protein electrophoresis (PE)** is fundamentally an **electrophoretic separation technique** that uses an **electric field** to separate charged protein molecules based on their **size, charge, and shape** - The core principle involves **migration of charged particles** through a medium (gel or capillary) under the influence of an electric field - Common types include **SDS-PAGE**, **native PAGE**, **isoelectric focusing**, and **capillary electrophoresis** - This is the standard classification in all major biochemistry textbooks (Harper's, Lehninger) *Chromatographic technique* - **Chromatography** separates molecules based on differential partitioning between a **stationary phase** and a **mobile phase** (not an electric field) - Examples include **HPLC**, **gas chromatography**, and **column chromatography** - Different separation principle from electrophoresis *Immunological technique* - **Immunological techniques** primarily use **antigen-antibody interactions** for detection, such as **ELISA**, **immunoprecipitation**, or **Western blot** - While **immunofixation electrophoresis** combines both principles, standard PE does not rely on immunological reactions for separation *Spectroscopic technique* - **Spectroscopy** involves studying the interaction between matter and **electromagnetic radiation** (e.g., **UV-Vis spectrophotometry**, **NMR**, **mass spectrometry**) - While electrophoresis results may be **detected** using spectroscopic methods (like densitometry after staining), the separation technique itself is electrophoretic, not spectroscopic - Detection method ≠ separation technique

Practice by Chapter

Spectrophotometry and Colorimetry

Practice Questions

Chromatography Techniques

Practice Questions

Electrophoresis and Applications

Practice Questions

Centrifugation and Ultracentrifugation

Practice Questions

Radioisotope Techniques

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Enzyme-Linked Immunosorbent Assay (ELISA)

Practice Questions

Polymerase Chain Reaction (PCR)

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Blotting Techniques: Southern, Northern, Western

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Mass Spectrometry in Biochemistry

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Recombinant DNA Technology

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DNA Sequencing

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Proteomics and Metabolomics

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