Glycosylation and Glycoproteins — MCQs
Which of the following protein molecules is responsible for cell-to-cell adhesion?
Which of the following is the platinum-based chemotherapeutic agent used as first-line treatment for ovarian carcinoma?
Which carbon of glucose is oxidized to form glucuronic acid?
Glycogen storage disorders are primarily classified under which type of disorders?
GlcNAc-P-P-oligosaccharide is -
Which of the following binds to Tyrosine Kinase receptor?
Name the antigen marked as X determining blood group A.
Protein segregation occurs in which organelle?
Insulin is essential for the entry of glucose into which of the following tissues?
Which carbohydrate is most lipogenic?
Glycosylation and Glycoproteins Indian Medical PG Practice Questions and MCQs
Question 1: Which of the following protein molecules is responsible for cell-to-cell adhesion?
- A. Laminin
- B. Fibronectin
- C. Collagen
- D. Cadherin (Correct Answer)
Explanation: ***Cadherin*** - **Cadherins** are transmembrane proteins that mediate **direct cell-to-cell adhesion** in a calcium-dependent manner - They form **adherens junctions** and **desmosomes**, which are essential for maintaining tissue integrity - Cadherins on adjacent cells bind to each other (**homophilic binding**), creating strong cell-cell connections - Critical for **embryonic development**, tissue architecture, and **epithelial barrier function** *Fibronectin* - **Fibronectin** is an extracellular matrix glycoprotein that mediates **cell-to-ECM adhesion**, not direct cell-to-cell adhesion - It binds to **integrins** on the cell surface, facilitating cell attachment to the extracellular matrix - Important for cell migration, wound healing, and embryonic development - Does not directly connect cells to each other *Collagen* - **Collagen** is the most abundant structural protein providing **tensile strength** to connective tissues - Primarily functions as **extracellular scaffolding**, not as an adhesion molecule - Provides mechanical support but does not mediate cell-cell adhesion *Laminin* - **Laminins** are major components of the **basal lamina** (basement membrane) - Mediate **cell-to-basal lamina adhesion** through integrin receptors - Important for cell differentiation, migration, and tissue organization - Function in cell-to-ECM adhesion, not cell-to-cell adhesion
Question 2: Which of the following is the platinum-based chemotherapeutic agent used as first-line treatment for ovarian carcinoma?
- A. Cyclophosphamide
- B. Methotrexate
- C. Cisplatin (Correct Answer)
- D. Dacarbazine
Explanation: ***Cisplatin*** - **Cisplatin** is a platinum-based chemotherapy drug that forms **DNA cross-links**, inhibiting DNA synthesis and leading to the death of rapidly dividing cells, making it highly effective against **ovarian carcinoma**. - It is a cornerstone of chemotherapy regimens for ovarian cancer, often used in combination with other agents such as paclitaxel. *Methotrexate* - **Methotrexate** is an **antimetabolite** that inhibits dihydrofolate reductase, thereby interfering with DNA synthesis. - While it is used in various cancers like leukemia, lymphoma, and some solid tumors (e.g., breast cancer, gestational trophoblastic disease), it is **not a primary recommended drug for ovarian carcinoma**. *Cyclophosphamide* - **Cyclophosphamide** is an **alkylating agent** that causes DNA damage, leading to cell death. - It is used in many cancers, including lymphoma, breast cancer, and some leukemias, but it is **not a first-line or primary agent for ovarian carcinoma** in contemporary treatment guidelines. *Dacarbazine* - **Dacarbazine** is an **alkylating agent** primarily used in the treatment of **malignant melanoma** and Hodgkin lymphoma. - It is **not indicated for the treatment of ovarian carcinoma**.
Question 3: Which carbon of glucose is oxidized to form glucuronic acid?
- A. Oxidation of the aldehyde group only
- B. No oxidation occurs
- C. Oxidation of the terminal alcohol group only (Correct Answer)
- D. Oxidation of both the aldehyde and terminal alcohol groups
Explanation: ***Oxidation of the terminal alcohol group only*** - Glucuronic acid is formed by the **oxidation of the C6 carbon (terminal alcohol group)** of glucose, while the aldehyde group (C1) remains intact. - This specific oxidation converts glucose into a **uronic acid**, essential for detoxification and connective tissue synthesis. *Oxidation of the aldehyde group only* - The oxidation of the **aldehyde group (C1)** of glucose would yield **gluconic acid**, not glucuronic acid. - This reaction typically occurs during the conversion of glucose to gluconolactone, a step in the pentose phosphate pathway for example. *No oxidation occurs* - The formation of glucuronic acid is explicitly an **oxidative process**, as a hydroxyl group is converted to a carboxyl group. - If no oxidation occurred, glucose would remain glucose, or undergo other non-oxidative transformations. *Oxidation of both the aldehyde and terminal alcohol groups* - Oxidation of **both the aldehyde (C1) and terminal alcohol (C6)** groups of glucose would lead to the formation of **glucaric acid (saccharic acid)**. - Glucaric acid has carboxyl groups at both ends, making it different from glucuronic acid, which only has a carboxyl group at C6.
Question 4: Glycogen storage disorders are primarily classified under which type of disorders?
- A. Endocrine disorders
- B. Metabolic disorders (Correct Answer)
- C. Genetic disorders
- D. Lysosomal storage disorders
Explanation: ***Metabolic disorders*** - Glycogen storage disorders involve defects in the enzymes responsible for **glycogen synthesis** or degradation. - These enzymatic defects lead to abnormal accumulation or breakdown of **glycogen**, thus affecting cellular metabolism. *Genetic disorders* - While glycogen storage disorders are **inherited** and thus genetic, their primary classification focuses on the **metabolic pathways** affected. - This category is too broad and refers to the origin, not the specific functional impairment. *Lysosomal storage disorders* - These disorders involve defective lysosomal enzymes leading to the accumulation of various **substrates within lysosomes**. - Glycogen storage disorders primarily involve enzymes in the **cytoplasm** (or sometimes lysosomes for Pompe disease, but the general classification is metabolic). *Endocrine disorders* - Endocrine disorders involve dysfunction of **hormone production** or regulation. - Glycogen storage diseases are disorders of **carbohydrate metabolism** and do not directly involve hormonal imbalance as their primary pathology.
Question 5: GlcNAc-P-P-oligosaccharide is -
- A. Proteoglycan
- B. Glycoprotein (Correct Answer)
- C. Collagen
- D. Phospholipid
Explanation: ***Glycoprotein*** - **GlcNAc-P-P-oligosaccharide** refers to the **N-linked oligosaccharide precursor** that is synthesized on a **dolichol pyrophosphate** carrier (`-P-P`). This complex is characteristic of the initial stages of **N-linked glycosylation**, a process that forms glycoproteins. - **N-acetylglucosamine (GlcNAc)** is a crucial sugar residue found at the reducing end of this precursor, linking it to the dolichol carrier. *Proteoglycan* - Proteoglycans consist of a **core protein** covalently attached to long, unbranched **glycosaminoglycan (GAG)** chains, such as chondroitin sulfate or heparin. - While they contain sugar units, their structure and synthesis pathway are distinct from the GlcNAc-P-P-oligosaccharide described, which is specific to N-linked glycoprotein synthesis. *Collagen* - **Collagen** is a fibrous protein, primarily composed of a triple helix of polypeptide chains rich in **glycine, proline, and hydroxyproline**. - Although collagen undergoes some post-translational modifications like **glycosylation**, it does not involve the GlcNAc-P-P-oligosaccharide precursor in its typical synthesis. *Phospholipid* - **Phospholipids** are a major component of cell membranes, composed of a **hydrophilic head** (containing a phosphate group) and two **hydrophobic fatty acid tails**. - They are lipids and do not contain carbohydrate structures like GlcNAc-P-P-oligosaccharide.
Question 6: Which of the following binds to Tyrosine Kinase receptor?
- A. Insulin (Correct Answer)
- B. Glucagon
- C. Prolactin
- D. Growth Hormone
Explanation: ***Insulin*** - **Insulin** is a classic example of a hormone that binds to and activates a **tyrosine kinase receptor**, leading to a cascade of intracellular signaling events for glucose uptake and metabolism. - The **insulin receptor** is a heterodimeric protein with intrinsic tyrosine kinase activity that phosphorylates itself and other proteins upon insulin binding. *Glucagon* - **Glucagon** primarily acts on **G protein-coupled receptors (GPCRs)**, specifically the glucagon receptor, to increase cyclic AMP (cAMP) and activate protein kinase A. - Its main roles are to stimulate **glycogenolysis** and **gluconeogenesis** in the liver. *Prolactin* - **Prolactin** binds to a receptor that is a member of the **cytokine receptor superfamily**, which lacks intrinsic enzyme activity. - Upon ligand binding, these receptors associate with and activate **Janus kinases (JAKs)**, leading to the JAK-STAT signaling pathway. *Growth Hormone* - **Growth hormone (GH)** also binds to a receptor belonging to the **cytokine receptor superfamily** (similar to prolactin), which then associates with and activates **JAKs**. - This activation subsequently initiates the **JAK-STAT signaling pathway**, mediating its diverse growth-promoting and metabolic effects.
Question 7: Name the antigen marked as X determining blood group A.
- A. N-Acetyl-Glucosamine
- B. Dermatan sulphate
- C. Keratan sulfate
- D. N-Acetyl-Galactosamine (Correct Answer)
Explanation: ***N-Acetyl-Galactosamine*** - Blood group A antigens are formed by the addition of **N-acetylgalactosamine** to the H antigen precursor molecule on the surface of red blood cells. - This sugar modification is catalyzed by the **A transferase enzyme**, which is specific for N-acetylgalactosamine. *N-Acetyl-Glucosamine* - While N-acetylglucosamine is a component of many glycans, it is not the terminal sugar that defines the **blood group A antigen**. - **N-acetylglucosamine** is a key building block for the H antigen and other blood group precursors, but not the specific modifying sugar for A. *Dermatan sulphate* - **Dermatan sulfate** is a **glycosaminoglycan** primarily found in connective tissues, skin, and blood vessels. - It plays a role in wound healing and coagulation, but is not involved in **ABO blood group determination**. *Keratan sulfate* - **Keratan sulfate** is another **glycosaminoglycan** found in cartilage, cornea, and bone. - It contributes to tissue hydration and structural integrity, but it is not part of the **ABO blood group antigens**.
Question 8: Protein segregation occurs in which organelle?
- A. Peroxisomes
- B. ER
- C. Mitochondria
- D. Golgi apparatus (Correct Answer)
Explanation: ***Golgi apparatus*** - The **Golgi apparatus** is a central organelle for **protein modification, sorting, and packaging** into vesicles for delivery to various cellular destinations. - It acts as a "post office" of the cell, directing proteins to their correct locations through **segregation** into specific secretory or transport pathways. *Peroxisomes* - **Peroxisomes** are involved in **metabolic processes** such as fatty acid oxidation and detoxification. - While they import some proteins, their primary role is not in the overall **segregation** and trafficking of proteins for diverse cellular destinations. *ER* - The **endoplasmic reticulum (ER)** is where proteins are synthesized (rough ER) and undergo initial folding and modification, including glycosylation. - However, the ER's main function is protein synthesis and early modification, not the final **segregation** and sorting for transport to different cellular locations. *Mitochondria* - **Mitochondria** are primarily responsible for **ATP production** through cellular respiration and houses its own genome. - While mitochondria import specific proteins necessary for their function, they are not involved in the general **segregation** of proteins destined for other organelles or secretion.
Question 9: Insulin is essential for the entry of glucose into which of the following tissues?
- A. Most neurons in the cerebral cortex
- B. Renal tubular cells
- C. Skeletal muscles (Correct Answer)
- D. Mucosa of the small intestine
Explanation: **Explanation:** The entry of glucose into cells is mediated by a family of glucose transporters known as **GLUT**. The correct answer is **Skeletal muscles** because they primarily express **GLUT-4**, which is the only insulin-dependent glucose transporter. 1. **Why Skeletal Muscle is Correct:** In the resting state, GLUT-4 transporters are sequestered in intracellular vesicles. When insulin binds to its receptor, it triggers a signaling cascade that translocates these vesicles to the plasma membrane, allowing glucose uptake. This mechanism is also found in **Adipose tissue** and the **Heart**. 2. **Why Other Options are Incorrect:** * **Neurons (Cerebral Cortex):** Use **GLUT-3** (and GLUT-1), which has a high affinity for glucose and is insulin-independent, ensuring the brain receives glucose even during fasting. * **Renal Tubular Cells & Intestinal Mucosa:** These tissues utilize **SGLT-1 and SGLT-2** (Sodium-Glucose Linked Transporters) for active transport against a concentration gradient, and **GLUT-2** for facilitated diffusion. Both are insulin-independent. **NEET-PG High-Yield Pearls:** * **GLUT-1:** Found in RBCs and the Blood-Brain Barrier (Basal uptake). * **GLUT-2:** Bidirectional transporter found in the **Liver, Pancreas (B-cells), and Kidney**. It acts as a glucose sensor. * **GLUT-4:** The only **insulin-responsive** transporter (Muscle, Fat). * **GLUT-5:** Specifically a **Fructose** transporter found in the small intestine and spermatozoa. * **Exercise** can also trigger GLUT-4 translocation in skeletal muscle independent of insulin, which is why exercise helps manage Blood Glucose in Type 2 Diabetes.
Question 10: Which carbohydrate is most lipogenic?
- A. Glucose
- B. Galactose
- C. Fructose (Correct Answer)
- D. Starch
Explanation: **Explanation:** The correct answer is **Fructose**. Fructose is considered the most lipogenic carbohydrate because it bypasses the major rate-limiting step of glycolysis. **1. Why Fructose is the Correct Answer:** In the liver, glucose metabolism is strictly regulated by the enzyme **Phosphofructokinase-1 (PFK-1)**, which acts as a metabolic "gatekeeper." However, fructose enters glycolysis via the **fructose-1-phosphate pathway**, bypassing PFK-1. This leads to an unregulated, rapid influx of triose phosphates (DHAP and Glyceraldehyde-3-phosphate) into the glycolytic pathway. This "flooding" of the pathway results in an overproduction of **Acetyl-CoA**, which is then diverted toward **de novo lipogenesis** (fatty acid synthesis) and VLDL production, leading to hepatic steatosis and hypertriglyceridemia. **2. Why Other Options are Incorrect:** * **Glucose:** Its metabolism is tightly controlled by PFK-1. When ATP levels are high, PFK-1 is inhibited, slowing down the production of Acetyl-CoA and limiting lipogenesis. * **Galactose:** Galactose is primarily converted to Glucose-1-phosphate and enters the mainstream glucose metabolic pathway, thus remaining subject to the same regulatory constraints as glucose. * **Starch:** Starch is a complex polysaccharide composed of glucose units. Once digested, it is absorbed as glucose and follows the regulated glucose metabolic pathway. **3. High-Yield NEET-PG Clinical Pearls:** * **Essential Fructosuria:** Due to deficiency of **Fructokinase**; it is a benign condition. * **Hereditary Fructose Intolerance (HFI):** Due to deficiency of **Aldolase B**. It leads to intracellular trapping of Fructose-1-P, causing severe hypoglycemia and liver damage. * **Metabolic Syndrome:** High consumption of High-Fructose Corn Syrup (HFCS) is a major contributor to non-alcoholic fatty liver disease (NAFLD) and insulin resistance due to its high lipogenic potential.
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