What is the classification of Carcinoembryonic Antigen (CEA)?
Level of which of the following is not elevated in heart disease
The predominant isozyme of LDH in lung is:
What is the primary receptor for High-Density Lipoprotein (HDL) in cholesterol metabolism?
What is the primary role of calnexin and calreticulin in the endoplasmic reticulum?
Which gene is responsible for the production of COX type 3?
Which of the following acids is MOST commonly used as a reagent in medical laboratory analytical procedures?
Shadow casting is used in -
What is the molecular mass of Immunoglobulin G (IgG) in kilodaltons (kDa)?
What is the Net Protein Utilization (NPU) for eggs?
NEET-PG 2015 - Biochemistry NEET-PG Practice Questions and MCQs
Question 91: What is the classification of Carcinoembryonic Antigen (CEA)?
- A. Glycoprotein (Correct Answer)
- B. Lipoprotein
- C. Phosphoprotein
- D. Nucleoprotein
Explanation: ***Glycoprotein*** - Carcinoembryonic Antigen (CEA) is classified as a **glycoprotein** due to its structure, which consists of both **carbohydrate** and **protein** components. - This glycosylation is crucial for its function as a cell adhesion molecule and its recognition in diagnostic assays. *Lipoprotein* - **Lipoproteins** are complexes of lipids and proteins that function primarily in **lipid transport** in the blood. - CEA's primary role and structure are not related to lipid transport or being predominantly lipid-based. *Phosphoprotein* - A **phosphoprotein** is a protein that has been **covalently modified by the addition of a phosphate group**, a process crucial for cell signaling. - While proteins can be phosphorylated, the defining characteristic and major classification of CEA is its extensive glycosylation rather than phosphorylation state. *Nucleoprotein* - **Nucleoproteins** are proteins that are **structurally associated with nucleic acids** (DNA or RNA), such as histones or ribosomal proteins. - CEA does not have a structural or functional association with nucleic acids.
Question 92: Level of which of the following is not elevated in heart disease
- A. SGOT
- B. ALP
- C. LDH
- D. 5-nucleotidase (Correct Answer)
Explanation: ***5-nucleotidase*** - While other enzymes like LDH, SGOT, and ALP can be elevated in various conditions including heart disease (especially in the context of tissue damage), 5-nucleotidase is **not typically elevated in heart disease**. - Its elevation is more commonly associated with **biliary obstruction** or certain liver pathologies. *LDH* - **Lactate dehydrogenase (LDH)** is a marker of **cellular damage** and can be elevated in myocardial infarction, though it is less specific than troponins. - LDH levels rise later than CK-MB and remain elevated longer, indicating persistent tissue injury. *SGOT* - **Serum glutamic oxaloacetic transaminase (SGOT)**, also known as **aspartate aminotransferase (AST)**, is elevated in acute **myocardial infarction** due to cardiac muscle damage. - While it's a marker for cardiac injury, it's not specific as it's also highly concentrated in the liver. *ALP* - **Alkaline phosphatase (ALP)** can be mildly elevated in heart failure due to **hepatic congestion** caused by reduced cardiac output. - While its primary diagnostic significance is in bone and liver disease, its elevation in advanced heart disease is usually a secondary consequence.
Question 93: The predominant isozyme of LDH in lung is:
- A. LD-2
- B. LD-5
- C. LD-1
- D. LD-3 (Correct Answer)
Explanation: ***LD-3*** - **LD-3** is the predominant **LDH isozyme** found in the **lungs**, spleen, pancreas, and lymph nodes. - Its elevation often suggests conditions affecting these organs, such as pulmonary embolism or pancreatitis. *LD-1* - **LD-1** is primarily associated with the **heart** and **red blood cells**. - Elevated levels are typically seen in conditions like myocardial infarction and hemolytic anemia. *LD-2* - **LD-2** is also found in the **heart** and **red blood cells**, though typically in lower concentrations than LD-1 in the heart. - It is often elevated after an MI, but typically LD-1 is elevated higher than LD-2 after an MI. *LD-5* - **LD-5** is predominantly found in the **liver** and **skeletal muscle**. - Its increase is indicative of liver damage or muscle injury, such as hepatitis or muscular dystrophy.
Question 94: What is the primary receptor for High-Density Lipoprotein (HDL) in cholesterol metabolism?
- A. SR-BI (Correct Answer)
- B. LDLR
- C. HDLR
- D. SR-82
Explanation: ***SR-BI*** - **Scavenger Receptor class B type 1 (SR-BI)** is the primary receptor responsible for selective uptake of **cholesteryl esters** from HDL into cells, particularly the liver and steroidogenic tissues. - Unlike other lipoprotein receptors, SR-BI mediates the **selective transfer** of cholesterol without internalizing the entire HDL particle. *LDLR* - The **Low-Density Lipoprotein Receptor (LDLR)** is the primary receptor for **LDL** and very low-density lipoprotein (VLDL) remnants, mediating their endocytosis and degradation. - While it plays a crucial role in cholesterol metabolism, its main function is related to the uptake of **LDL cholesterol**, not HDL. *HDLR* - **HDLR** is not a recognized receptor in cholesterol metabolism. - This term may be a distracter created by combining HDL with the common receptor nomenclature. *SR-82* - **SR-82** is not a recognized receptor involved in cholesterol metabolism. - Similar to HDLR, this is a distracter term.
Question 95: What is the primary role of calnexin and calreticulin in the endoplasmic reticulum?
- A. Degrade misfolded proteins
- B. Act as chaperones (Correct Answer)
- C. Serve as tumor markers
- D. Facilitate enzymatic reactions
Explanation: ***Act as chaperones*** - **Calnexin** and **calreticulin** are **chaperone proteins** located in the **endoplasmic reticulum (ER)**. - They bind to unfolded or misfolded glycoproteins to assist in their proper folding and assembly. - They are part of the **ER quality control system**, ensuring only properly folded proteins proceed to the Golgi apparatus. *Degrade misfolded proteins* - While misfolded proteins are eventually degraded through **ER-associated degradation (ERAD)**, this is not the primary function of calnexin and calreticulin. - These chaperones first attempt to **rescue and refold** proteins; degradation is a separate process involving other machinery. *Serve as tumor markers* - **Calnexin** and **calreticulin** are not typically used as **tumor markers** in clinical practice. - Their functions are related to protein quality control within the cell, not cancer detection. *Facilitate enzymatic reactions* - While some proteins in the ER are enzymes, **calnexin** and **calreticulin** themselves are not enzymes, nor do they primarily facilitate enzymatic reactions. - Their function is to ensure correct protein folding, distinct from direct catalytic activity.
Question 96: Which gene is responsible for the production of COX type 3?
- A. COX 3 gene
- B. COX 2 gene
- C. None of the above
- D. COX I gene (Correct Answer)
Explanation: ***COX I gene*** - COX-3 is an **alternatively spliced variant** of the **COX-1 gene** (specifically, a splice variant of the COX-1 mRNA that retains intron 1). - While it was initially thought to be a distinct gene, research has shown that it arises from the same genetic locus as COX-1. *COX 2 gene* - The COX-2 gene encodes for the **inducible cyclooxygenase enzyme**, which is responsible for prostaglandin synthesis during inflammation. - It is a separate gene from COX-1 and has distinct regulatory mechanisms and physiological roles. *COX 3 gene* - There is currently **no distinct gene in humans** specifically identified as "COX-3". - COX-3 refers to a protein isoform derived from the COX-1 gene, not a separate genetic locus. *None of the above* - This option is incorrect because COX-3 is indeed derived from the **COX-1 gene** through alternative splicing. - The existence of COX-3 as a distinct protein product has been demonstrated, although its precise physiological role in humans is still under investigation.
Question 97: Which of the following acids is MOST commonly used as a reagent in medical laboratory analytical procedures?
- A. Nitric acid is used in chemical analysis.
- B. Carbolic acid is used as a disinfectant.
- C. Oxalic acid is used in various laboratory applications.
- D. Sulphuric acid is used in various laboratory processes. (Correct Answer)
Explanation: ***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
Question 98: 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.
Question 99: What is the molecular mass of Immunoglobulin G (IgG) in kilodaltons (kDa)?
- A. 150 (Correct Answer)
- B. 400
- C. 1000
- D. 1500
Explanation: **\*Correct Option: 150 kDa\*** - **Immunoglobulin G (IgG)** is the most abundant antibody in human serum and has a characteristic molecular mass of approximately **150 kDa**. - This mass is attributed to its structure, comprising two identical **heavy chains** (~50 kDa each) and two identical **light chains** (~25 kDa each). - IgG represents about **75-80% of total serum immunoglobulins** and is the main antibody involved in secondary immune responses. *Incorrect Option: 400 kDa* - A molecular mass of **400 kDa** is significantly higher than that of a monomeric IgG molecule. - This mass is closer to **IgM pentamers** (~900 kDa) or large protein complexes, but still does not match any standard immunoglobulin structure. *Incorrect Option: 1000 kDa* - A molecular mass of **1000 kDa (1 MDa)** is far too large for a single IgG molecule. - This weight typically corresponds to very large macromolecular structures or aggregates, such as **ribosomes** or large enzyme complexes. *Incorrect Option: 1500 kDa* - A molecular mass of **1500 kDa (1.5 MDa)** is extremely large for an individual antibody. - Such a mass would be characteristic of very large protein assemblies, viral capsids, or cellular components, not a soluble antibody.
Question 100: What is the Net Protein Utilization (NPU) for eggs?
- A. 70
- B. 80
- C. 94 (Correct Answer)
- D. 100
Explanation: ***94*** - **Eggs** are considered a **high-quality protein source** with a Net Protein Utilization (NPU) of approximately **94**, indicating very efficient protein absorption and utilization by the body. - This high NPU reflects the excellent balance of **essential amino acids** in eggs, making them a benchmark for protein quality. *70* - An NPU of 70 is generally considered good but is lower than that of **eggs**, which are among the most efficiently utilized proteins. - This value might be typical for some **plant-based proteins** or mixtures of proteins with slightly less optimal essential amino acid profiles. *80* - An NPU of 80 indicates good protein quality but is still significantly lower than the **NPU of eggs**. - This value is often seen in high-quality **meat proteins** or well-balanced **dairy products**. *100* - An NPU of 100 would mean that all ingested protein is perfectly absorbed and utilized by the body without any loss, which is **theoretically impossible** for biological systems. - While some protein quality metrics might approach 100, **NPU is a measure of actual utilization** and never reaches 100 due to metabolic losses.