Biochemical Techniques — MCQs

Biochemical Techniques Indian Medical PG Practice Questions and MCQs

Question 231: For DNA extraction from blood samples, the preferred anticoagulant is:

A. EDTA (Correct Answer)
B. Plain bulb
C. Formalin
D. None of the options

Explanation: ***EDTA*** - **EDTA** (ethylenediaminetetraacetic acid) acts as an anticoagulant by **chelating calcium ions**, which are essential for the coagulation cascade, making it ideal for DNA extraction. - Using an EDTA collection tube ensures that the blood sample remains in its liquid state, preventing clot formation which can trap DNA and make isolation difficult. *Plain bulb* - A plain bulb refers to a tube without any anticoagulant, allowing the blood to **clot naturally**. - While serum can be obtained from such a tube, the DNA would be entrapped within the clot, making its extraction **less efficient and potentially damaging**. *Formalin* - **Formalin** (a solution of formaldehyde) is a fixative used to preserve tissue morphology by **cross-linking proteins**. - While useful for histopathology, it **damages DNA** through chemical modifications and fragmentation, making it unsuitable for DNA isolation or genetic analysis. *None of the options* - This option is incorrect because **EDTA is a widely recognized and appropriate** anticoagulant for preserving DNA samples from blood for molecular studies.

Question 232: If a biochemical test gives the same reading for a sample on repeated testing, it is inferred that the measurement is -

A. Specific
B. Accurate
C. Sensitive
D. Precise (Correct Answer)

Explanation: ***Precise*** - **Precision** refers to the consistency or **reproducibility** of measurements. If repeated tests yield similar results, the measurement is considered precise. - A precise test may not necessarily be accurate, but it consistently gives the same value, highlighting its **reliability** in producing repeatable results. *Specific* - **Specificity** refers to a test's ability to correctly identify individuals who do **not** have a particular condition (i.e., true negatives). - It measures how well a test avoids **false positives**, indicating that a positive result is truly associated with the target analyte. *Accurate* - **Accuracy** refers to how close a measured value is to the true or **actual value**. - A test is accurate if it provides results that are close to the correct value, not simply if they are consistently the same. *Sensitive* - **Sensitivity** refers to a test's ability to correctly identify individuals who **do** have a particular condition (i.e., true positives). - It measures how well a test avoids **false negatives**, indicating that a negative result truly means the condition is absent.

Question 233: Which one of the following enzymes is obtained from Thermus aquaticus bacterium that is heat stable and used in PCR at high temperature?

A. DNA gyrase
B. DNA polymerase III
C. Taq polymerase (Correct Answer)
D. Endonuclease

Explanation: ***Taq polymerase*** - This **heat-stable DNA polymerase** is isolated from the thermophilic bacterium *Thermus aquaticus*. - Its ability to withstand high temperatures makes it ideal for the **polymerase chain reaction (PCR)**, where DNA denaturation steps occur at elevated temperatures. *DNA gyrase* - **DNA gyrase** is a type II topoisomerase that introduces negative supercoils into DNA, which is important for DNA replication and transcription. - It is not heat-stable and is not directly used for DNA amplification in PCR. *DNA polymerase III* - **DNA polymerase III** is the primary enzyme responsible for DNA replication in *E. coli* and other bacteria. - It rapidly synthesizes DNA but is **not heat-stable** and would denature at the temperatures required for PCR. *Endonuclease* - **Endonucleases** are enzymes that cleave phosphodiester bonds within a polynucleotide chain. - While essential for processes like DNA repair and restriction mapping, they are not primarily involved in and are not heat-stable for DNA synthesis in PCR.

Question 234: DNA polymerase used in PCR is derived from which organism?

A. Bacteriophages
B. Thermus aquaticus (Correct Answer)
C. E. coli
D. Retroviruses

Explanation: ***Thermus aquaticus*** - The **DNA polymerase** used in PCR is typically isolated from the bacterium **Thermus aquaticus**, known as **Taq polymerase**. - This enzyme is chosen because of its **thermostability**, meaning it can withstand the high temperatures required to denature DNA during each PCR cycle without degrading. *Bacteriophages* - **Bacteriophages** are viruses that infect bacteria, and while some encode their own **DNA polymerases**, these are generally not thermostable enough for PCR. - Phage-derived polymerases are used in other molecular biology techniques but not typically in standard PCR due to thermal instability. *E. coli* - **E. coli** produces **DNA polymerase I**, which is essential for DNA replication and repair in the cell but is **not thermostable**. - Its polymerase would denature at the high temperatures used in the PCR denaturation step, rendering it unsuitable for the reaction. *Retroviruses* - **Retroviruses** primarily encode **reverse transcriptase**, which is an RNA-dependent DNA polymerase. - This enzyme synthesizes DNA from an RNA template and is not suitable for the DNA-dependent DNA synthesis required in standard PCR.

Question 235: Isotopes of an element have the same:

A. Atomic number (Correct Answer)
B. Neutron number
C. Mass number
D. Electron number

Explanation: ***Atomic number*** - Isotopes are defined as atoms of the same element, meaning they have the same number of **protons**, which determines the atomic number. - The atomic number is unique to each element and dictates its **chemical properties**. - This is the **defining characteristic** that makes isotopes belong to the same element (e.g., C-12, C-13, and C-14 all have 6 protons). *Neutron number* - Isotopes of an element differ in their number of **neutrons**, leading to variations in their mass. - This difference in neutron count is precisely what distinguishes one isotope from another. - For example, C-12 has 6 neutrons while C-14 has 8 neutrons. *Mass number* - The **mass number** is the sum of protons and neutrons in an atom's nucleus. - Since isotopes have different numbers of neutrons, they will also have different mass numbers. - This is why isotopes have different mass designations (C-12 vs C-14). *Electron number* - While neutral atoms of isotopes have the same electron number (equal to the atomic number), this is not always true for **ions**. - Isotopes can gain or lose electrons to form ions with different electron numbers. - The atomic number (protons) remains the **fundamental invariant property** that defines isotopes as belonging to the same element, regardless of ionization state.

Question 236: Which of the following techniques uses radioisotopes?

A. Sequencing of nucleic acid
B. Mass spectroscopy
C. ELISA
D. RIA (Correct Answer)

Explanation: ***RIA*** - **Radioimmunoassay (RIA)** is a highly sensitive immunoassay that uses **radioisotopes** to label antigens or antibodies. - The detection of the labeled component allows for the quantification of substances in very low concentrations, often in biological fluids. *Sequencing of nucleic acid* - **Nucleic acid sequencing** determines the order of nucleotides in DNA or RNA, historically using methods like Sanger sequencing which employed **dideoxynucleotides** labeled with fluorescent dyes, not radioisotopes for routine detection. Modern methods often use next-generation sequencing technologies without radioisotopes. - While early methods for DNA sequencing, such as the original Maxam-Gilbert method, did utilize radioisotopes for labeling DNA fragments, this is not the technique primarily associated with general nucleic acid sequencing today, which has largely moved to fluorescent or semiconductor-based detection. *Mass spectroscopy* - **Mass spectroscopy** works by ionizing samples and measuring the **mass-to-charge ratio** of the ions to identify compounds, not by incorporating radioisotopes. - It is used for identifying unknown compounds, quantifying known compounds, and elucidating the structure and chemical properties of molecules. *ELISA* - **Enzyme-linked immunosorbent assay (ELISA)** uses an **enzyme** conjugated to an antibody or antigen, which then catalyzes a colorimetric or chemiluminescent reaction for detection. - It does not involve the use of radioisotopes for labeling or detection.

Question 237: Among the biochemical methods of genetic engineering, the Western Blot detects:

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

Explanation: ***Protein*** - **Western blot** (also known as protein immunoblot) is a widely used analytical technique in molecular biology and immunogenetics to detect specific **proteins** in a 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. *DNA* - **DNA** is typically detected using techniques like **Southern blot** or **PCR (Polymerase Chain Reaction)**. - Western blot is not designed to recognize nucleic acids, but rather uses antibodies that bind to specific protein epitopes. *mRNA* - **mRNA** (messenger RNA) is analyzed using methods like **Northern blot** or **RT-PCR (Reverse Transcription PCR)**. - These techniques specifically target RNA sequences and involve RNA extraction, separation, and hybridization with complementary probes. *RNA* - The general term **RNA** encompasses various types including mRNA, tRNA, and rRNA; Northern blot is the most common method for detecting specific RNA molecules. - Western blot, being an antibody-based assay, is specific for the detection and quantification of **proteins**.

Question 238: Southern blotting is used for:

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

Explanation: ***DNA*** - **Southern blotting** is a molecular biology technique used to detect specific **DNA sequences** in DNA samples. - It involves **electrophoresis** to separate DNA fragments by size, followed by transfer to a membrane and hybridization with a labeled **DNA probe**. *Protein* - The technique used to detect specific **proteins** is called **Western blotting**, not Southern blotting. - **Western blotting** involves protein separation by **gel electrophoresis**, transfer to a membrane, and detection using specific **antibodies**. *Antibody* - While antibodies are used as probes in techniques like Western blotting, antibodies themselves are not directly analyzed by Southern blotting. - Techniques like ELISA (Enzyme-Linked Immunosorbent Assay) are commonly used to detect and quantify **antibodies** in a sample. *RNA* - The technique used to detect specific **RNA sequences** is called **Northern blotting**. - **Northern blotting** follows a similar principle to Southern blotting but uses **RNA** as the target molecule instead of DNA.

Question 239: Northern blot is used for the detection of which of the following?

A. Protein DNA interaction
B. DNA
C. mRNA (Correct Answer)
D. Protein

Explanation: ***mRNA*** - **Northern blot** is a laboratory technique used to detect specific **mRNA molecules** among a mixture of RNA. - It involves separating RNA samples by size via **gel electrophoresis**, then transferring them to a membrane and hybridizing with a labeled probe. *Protein DNA interaction* - Techniques like **Chromatin Immunoprecipitation (ChIP)** or **Electrophoretic Mobility Shift Assay (EMSA)** are used to study protein-DNA interactions. - Northern blot does not analyze the binding of proteins to DNA. *DNA* - **Southern blot** is the technique specifically designed for the detection and analysis of specific **DNA sequences**. - It involves electrophoresis of DNA, transfer to a membrane, and hybridization with a DNA probe. *Protein* - **Western blot** is the primary technique used for the detection and analysis of specific **proteins**. - It involves protein electrophoresis, transfer to a membrane, and detection using specific antibodies.

Question 240: Techniques used for protein expression proteomics study include:

A. PolyAcrylamide Gel Electrophoresis (PAGE)
B. Gene Expression Analysis (indirectly related to proteomics)
C. Mass Spectrometry
D. All of the options (Correct Answer)

Explanation: ***All of the options*** - All listed techniques—**Polyacrylamide Gel Electrophoresis (PAGE)**, **Gene Expression Analysis**, and **Mass Spectrometry**—are used in protein expression proteomics studies, either directly or indirectly, to analyze and quantify proteins. - The integration of these various techniques provides a comprehensive approach to understanding protein expression profiles. *PolyAcrylamide Gel Electrophoresis (PAGE)* - **PAGE** (including 1D and 2D-PAGE) is a fundamental technique for separating proteins based on their **molecular weight** and **isoelectric point**, which is crucial for visualizing and quantifying expressed proteins. - It often serves as an initial separation step before more detailed analysis, such as **mass spectrometry**. *Gene Expression Analysis (indirectly related to proteomics)* - Although **gene expression analysis** (e.g., using **RT-PCR** or **microarrays**) measures mRNA levels, it is indirectly related to proteomics because mRNA levels often **correlate with protein levels**. - It provides insights into the **transcriptional regulation** that influences protein expression, complementing direct protein analysis. *Mass Spectrometry* - **Mass spectrometry** is a powerful and widely used technique in proteomics for **identifying, quantifying, and characterizing proteins** and peptides by measuring their **mass-to-charge ratio**. - It can be used for both **discovery proteomics** (identifying novel proteins) and **targeted proteomics** (quantifying specific proteins).

Practice by Chapter

Spectrophotometry and Colorimetry

Practice Questions

Chromatography Techniques

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Electrophoresis and Applications

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Centrifugation and Ultracentrifugation

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Radioisotope Techniques

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Enzyme-Linked Immunosorbent Assay (ELISA)

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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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