Biochemical Techniques Practice Questions

Q: What is the study of the multiplication of proteins in a disease process called?

Proteomics. ### Explanation **1. Why Proteomics is Correct:** **Proteomics** is the large-scale study of the entire set of proteins (the proteome) expressed by a genome, cell, tissue, or organism. In a disease process, protein expression patterns change—certain proteins may be overexpressed (multiplied), modified, or downregulated. Studying these changes helps in identifying biomarkers for diagnosis and understanding the pathophysiology of diseases like cancer or neurodegenerative disorders. **2. Analysis of Incorrect Options:** * **Genomics (Option B):** This is the study of the complete set of DNA (genes) within an organism. While it provides the blueprint, it does not account for post-translational modifications or the actual functional state of the cell during disease. * **Glycomics (Option C):** This focuses on the study of **glycans** (sugars/carbohydrates) and their structures and functions, particularly how they attach to proteins and lipids. * **Nucleomics (Option D):** This is a less common term referring to the study of the **nucleome**—the complete set of components in the cell nucleus, including its 3D architecture and regulatory elements. **3. Clinical Pearls & High-Yield Facts for NEET-PG:** * **Central Dogma Flow:** Genomics (DNA) → Transcriptomics (mRNA) → Proteomics (Proteins) → Metabolomics (Metabolites). * **Techniques:** The "Gold Standard" for proteomics is **Mass Spectrometry (MS)**, often preceded by **2D-Gel Electrophoresis** to separate proteins. * **Dynamic Nature:** Unlike the genome, which is relatively constant, the **proteome is highly dynamic** and changes constantly in response to internal and external stimuli (stress, drugs, or disease). * **Clinical Application:** PSA (Prostate-Specific Antigen) and Troponin are classic examples of protein biomarkers studied via proteomic principles for clinical diagnosis.

Q: Fluoride is used in which type of samples for biochemical estimations?

Blood glucose estimation samples. **Explanation:** **1. Why Option A is Correct:** Sodium fluoride (NaF) is the preferred additive for **blood glucose estimation** because it acts as a potent **antiglycolytic agent**. In a blood sample, RBCs and WBCs continue to metabolize glucose via the glycolytic pathway even after collection, leading to a decrease in glucose levels by approximately 5–7% per hour. Fluoride ions inhibit the enzyme **Enolase** (which converts 2-phosphoglycerate to phosphoenolpyruvate) by forming a complex with magnesium and phosphate. This "locks" the glucose concentration, ensuring an accurate measurement of the patient's glycemic status at the time of draw. It is typically used in combination with Potassium Oxalate (anticoagulant) in the **Grey-top Vacutainer**. **2. Why Other Options are Incorrect:** * **Option B & C:** Fluoride is not used for **urine glucose estimation**. In urine, glucose is typically detected using semi-quantitative methods like Benedict’s test or glucose oxidase strips. The primary concern in urine samples is bacterial growth, which is managed by preservatives like Thymol or Toluene, rather than antiglycolytic agents. * **Option D:** This is incorrect as the application of fluoride in blood chemistry is a standard laboratory practice. **3. NEET-PG High-Yield Pearls:** * **The "Enolase" Connection:** Always remember that Fluoride inhibits Enolase. This is a frequent "match the following" or "assertion-reason" question. * **Urease Inhibition:** Fluoride also inhibits the enzyme **Urease**. Therefore, fluoride-containing samples **cannot** be used for urea estimation if the laboratory uses the urease method. * **Timing:** While fluoride inhibits glycolysis, its effect is not instantaneous (it takes 1-2 hours to fully inhibit the enzyme). For immediate results, the sample should be centrifuged and plasma separated promptly.

Q: Which enzyme is used in Polymerase Chain Reaction (PCR)?

Taq polymerase. **Explanation:** **Taq polymerase** is the correct answer because it is a **thermostable DNA polymerase** derived from the bacterium *Thermus aquaticus*. The PCR process involves repeated cycles of high temperatures (94–96°C) for DNA denaturation. Unlike human DNA polymerase, which would denature and lose function at these temperatures, Taq polymerase remains stable and active, allowing it to synthesize new DNA strands by adding deoxynucleotides (dNTPs) to a primer. **Analysis of Incorrect Options:** * **Reverse transcriptase:** This enzyme synthesizes DNA from an RNA template. While used in **RT-PCR** (to study RNA viruses like HIV or SARS-CoV-2), it is not the standard enzyme for the classical PCR process which amplifies DNA. * **RNA polymerase:** This enzyme synthesizes RNA from a DNA template during transcription. It is not involved in DNA amplification or the PCR cycle. **High-Yield Clinical Pearls for NEET-PG:** * **Steps of PCR:** 1. Denaturation (~95°C), 2. Annealing (~55°C), 3. Extension (~72°C). * **Components required:** Template DNA, Primers (forward and reverse), dNTPs, Taq polymerase, and $Mg^{2+}$ (cofactor). * **Applications:** Diagnosis of genetic mutations (e.g., Sickle cell anemia), detection of infectious agents (TB, Hepatitis), and forensic medicine (DNA fingerprinting). * **Pfu Polymerase:** Another thermostable enzyme used when higher "proofreading" accuracy is required, as Taq lacks 3' to 5' exonuclease activity.

Q: What is the most accurate technique for quantifying gene expression?

Real-Time Reverse Transcriptase PCR. **Explanation:** **Why Real-Time Reverse Transcriptase PCR (qRT-PCR) is correct:** Gene expression is measured by the amount of mRNA produced by a specific gene. To quantify this, mRNA must first be converted into complementary DNA (cDNA) using the enzyme **Reverse Transcriptase**. While standard PCR only allows for "end-point" detection, **Real-Time PCR (qPCR)** monitors the amplification process as it occurs using fluorescent dyes or probes. This allows for the precise quantification of the initial amount of template RNA. Therefore, qRT-PCR is the "gold standard" for sensitive and accurate quantification of gene expression. **Analysis of Incorrect Options:** * **Northern Blot:** This is a classical technique used to detect specific RNA sequences. However, it is labor-intensive, requires large amounts of RNA, and is significantly less sensitive and less quantitative than PCR-based methods. * **PCR (Polymerase Chain Reaction):** Standard PCR amplifies DNA, not RNA. Without the reverse transcription step, it cannot measure gene expression. * **Reverse Transcriptase PCR (RT-PCR):** While this converts RNA to DNA for amplification, it is typically a **semi-quantitative** or qualitative "end-point" analysis. It tells you if a gene is expressed but does not provide the high-level accuracy of "Real-Time" monitoring for quantification. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard for COVID-19:** qRT-PCR is the definitive diagnostic test for SARS-CoV-2, detecting viral RNA. * **Ct Value (Cycle Threshold):** In Real-Time PCR, a lower Ct value indicates a higher initial viral load or higher gene expression. * **Southern vs. Northern vs. Western:** Remember the mnemonic **SNOW DROP** (Southern-DNA, Northern-RNA, Western-Protein).

Q: What color does a positive Fouchet's test yield?

Green. **Explanation:** **Fouchet’s test** is a qualitative biochemical method used to detect the presence of **bilirubin** in urine. This is a crucial diagnostic tool for identifying obstructive jaundice or hepatocellular jaundice, where conjugated bilirubin is excreted in the urine (bilirubinuria). 1. **Why Green is Correct:** The test relies on the oxidation of bilirubin. When Fouchet’s reagent (which contains trichloroacetic acid and ferric chloride) is added to urine pre-treated with barium chloride, the ferric chloride acts as an oxidizing agent. It oxidizes the yellow-colored **bilirubin** into **biliverdin**, which is **green** in color. A positive result is indicated by the appearance of a green or bluish-green precipitate. 2. **Analysis of Incorrect Options:** * **Red:** This is characteristic of a positive **Rothera’s test** (detecting ketones) or a positive **Benzidine test** (detecting blood/hemoglobin). * **Violet:** A violet or purple ring is seen in the **Hopkins-Cole test** (for tryptophan) or the **Biuret test** (for proteins). * **Yellow:** This is the baseline color of normal urine and the color of bilirubin itself before oxidation. **High-Yield Clinical Pearls for NEET-PG:** * **Principle:** Oxidation of bilirubin to biliverdin. * **Reagent Components:** Trichloroacetic acid (precipitates proteins) and Ferric chloride (oxidizing agent). * **Clinical Significance:** Bilirubin appears in urine only when it is **conjugated** (water-soluble). Therefore, Fouchet’s test is positive in obstructive and hepatic jaundice but **negative in hemolytic jaundice** (where unconjugated bilirubin predominates). * **Pre-step:** Barium chloride is added first to concentrate the bilirubin by adsorbing it onto the barium sulfate precipitate.

Q: Xanthoproteic reaction is due to the formation of?

Trinitrophenol. **Explanation:** The **Xanthoproteic reaction** is a qualitative test used to detect the presence of proteins containing **aromatic amino acids** (specifically Tyrosine and Tryptophan; Phenylalanine gives a weak or negative result). **Why Trinitrophenol is correct:** When concentrated Nitric acid ($HNO_3$) is added to a protein solution, the aromatic rings of the amino acids undergo a **nitration reaction**. For example, Tyrosine reacts with nitric acid to form nitro-derivatives. Upon heating and subsequent addition of an alkali (like NaOH or $NH_4OH$), the yellow color intensifies to orange due to the formation of nitrated salts. **Trinitrophenol** (also known as Picric acid) is a representative polynitrated aromatic compound formed during this process, giving the characteristic yellow precipitate. **Analysis of Incorrect Options:** * **B. Mononitrophenol:** While nitration begins with a single nitro group, the reaction typically proceeds to higher degrees of nitration (polynitration) under the test conditions to produce the characteristic color. * **C. Nitric acid:** This is the **reagent** used to perform the test, not the product formed. * **D. Pyrocatechol:** This is a dihydroxybenzene derivative and is not a product of the nitration of aromatic amino acids in this reaction. **High-Yield Clinical Pearls for NEET-PG:** * **The "Yellow Skin" Sign:** If concentrated nitric acid accidentally spills on the skin, it turns yellow. This is a real-life Xanthoproteic reaction occurring with the proteins (keratin) in the skin. * **Amino Acids involved:** Tyrosine and Tryptophan are the primary responders. Phenylalanine is highly stable and usually does not react easily under standard test conditions. * **Key Reagent:** Concentrated $HNO_3$. * **Color Change:** Yellow (with acid) $\rightarrow$ Orange (with alkali).

Q: Which of the following is NOT required for a standard polymerase chain reaction?

Dideoxynucleotides. ### Explanation **Core Concept: Polymerase Chain Reaction (PCR)** PCR is an *in vitro* enzymatic method used to amplify specific DNA sequences. The process mimics natural DNA replication but requires specific components to function in a thermal cycler. **Why Dideoxynucleotides (ddNTPs) are NOT required:** Dideoxynucleotides (ddNTPs) lack a **3'-OH group**, which is essential for forming phosphodiester bonds. When a ddNTP is incorporated, DNA synthesis terminates immediately. Therefore, ddNTPs are used in **Sanger Sequencing (Chain Termination Method)**, not in standard PCR, where the goal is to synthesize full-length DNA strands. **Analysis of Other Options:** * **Taq Polymerase:** A heat-stable DNA polymerase (derived from *Thermus aquaticus*) required to extend the primers by adding nucleotides at high temperatures. * **dNTPs (dATP, dCTP, dGTP, dTTP):** These are the "building blocks" or substrates required to synthesize the new DNA strand. * **Magnesium ions (Mg²⁺):** These act as a mandatory **cofactor** for DNA polymerase activity. They stabilize the negative charges on the phosphate backbone and facilitate the catalysis of phosphodiester bonds. **High-Yield NEET-PG Pearls:** 1. **Steps of PCR:** Denaturation (94-96°C) → Annealing (50-65°C) → Extension (72°C). 2. **Primers:** PCR requires two synthetic, short oligonucleotide primers that are complementary to the 3' ends of the target DNA. 3. **RT-PCR:** Uses Reverse Transcriptase to convert RNA into cDNA before amplification (Gold standard for COVID-19 diagnosis). 4. **Real-Time PCR (qPCR):** Used to quantify the amount of DNA/RNA in a sample using fluorescent dyes.

Question 1

What is the study of the multiplication of proteins in a disease process called?

Accepted Answer

Proteomics

Answer

Genomics

Answer

Glycomics

Answer

Nucleomics

Question 2

Which of the following is NOT a method used for fusing two cells in genetic recombination techniques?

Accepted Answer

Fusion mediated by altering membrane viscosity

Answer

Fusion mediated by Ethylene Glycol

Answer

Fusion mediated by electric current

Answer

Fusion mediated by viral transformation

Question 3

Fluoride is used in which type of samples for biochemical estimations?

Accepted Answer

Blood glucose estimation samples

Answer

Urine glucose estimation samples

Answer

Both blood and urine glucose estimation samples

Answer

None of the above

Question 4

Movement of proteins from the nucleus to the cytoplasm can be observed using which technique?

Accepted Answer

Fluorescence Recovery After Photobleaching (FRAP)

Answer

Fluorescence in situ hybridization (FISH)

Answer

Confocal microscopy

Answer

Electron microscopy

Question 5

Which enzyme is used in Polymerase Chain Reaction (PCR)?

Accepted Answer

Taq polymerase

Answer

Reverse transcriptase

Answer

RNA polymerase

Answer

None of the above

Question 6

What is the most accurate technique for quantifying gene expression?

Accepted Answer

Real-Time Reverse Transcriptase PCR

Answer

Northern blot

Answer

PCR

Answer

Reverse Transcriptase PCR

Question 7

What color does a positive Fouchet's test yield?

Accepted Answer

Green

Answer

Red

Answer

Violet

Answer

Yellow

Question 8

Xanthoproteic reaction is due to the formation of?

Accepted Answer

Trinitrophenol

Answer

Mononitrophenol

Answer

Nitric acid

Answer

Pyrocathechol

Question 9

The conversion of an optically pure isomer into a mixture of equal amounts of both dextro and levo forms is called as?

Accepted Answer

Racemization

Answer

Polymerization

Answer

Stereoisomerism

Answer

Fractionation

Question 10

Which of the following is NOT required for a standard polymerase chain reaction?

Accepted Answer

Dideoxynucleotides

Answer

Taq polymerase

Answer

Deoxynucleotide triphosphates (dNTPs)

Answer

Magnesium ions

Biochemical Techniques — MCQs

Biochemical Techniques — MCQs

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