Carbohydrate Metabolism Practice Questions

Q: Which of the following hormones stimulates glucose utilization?

Insulin. **Explanation:** The regulation of blood glucose is a balance between **anabolic (hypoglycemic)** and **catabolic (hyperglycemic)** hormones. **Why Insulin is Correct:** Insulin is the only major anabolic hormone that lowers blood glucose by stimulating **glucose utilization**. It achieves this through three primary mechanisms: 1. **Increased Uptake:** It promotes the translocation of **GLUT-4** transporters to the cell membranes of skeletal muscle and adipose tissue. 2. **Glycolysis:** It activates key enzymes like Phosphofructokinase-1 (PFK-1) and Glucokinase, favoring glucose breakdown. 3. **Glycogenesis:** It stimulates Glycogen Synthase to store glucose as glycogen in the liver and muscles. **Why Other Options are Incorrect:** Options B, C, and D are all **counter-regulatory (diabetogenic) hormones** that increase blood glucose levels: * **Glucagon:** Stimulates hepatic glycogenolysis and gluconeogenesis during fasting states. * **Corticosteroids (Cortisol):** Increase gluconeogenesis and decrease peripheral glucose uptake (insulin resistance) to ensure glucose availability during stress. * **Growth Hormone:** Inhibits glucose uptake in peripheral tissues (anti-insulin effect) and stimulates lipolysis. **High-Yield NEET-PG Pearls:** * **GLUT-4** is the only insulin-dependent glucose transporter (found in heart, skeletal muscle, and adipose tissue). * **Brain and Liver** do not require insulin for glucose uptake (GLUT-1 and GLUT-2 respectively). * **Rate-limiting enzyme of Glycolysis:** Phosphofructokinase-1 (PFK-1), which is induced by insulin via Fructose 2,6-bisphosphate. * **C-peptide** levels can be used to differentiate endogenous insulin production from exogenous insulin injection.

Q: All of the following are glycogen storage disorders except?

All of the above. **Explanation:** This question tests your knowledge of **Glycogen Storage Disorders (GSDs)**, which are a group of inherited metabolic disorders caused by enzyme deficiencies affecting glycogen synthesis or breakdown. **1. Why "All of the above" is correct:** All three options listed are classic examples of Glycogen Storage Disorders. Each represents a deficiency in a specific enzyme required for glycogen metabolism: * **Pompe Disease (GSD Type II):** Caused by a deficiency of **Acid α-1,4-glucosidase** (Acid Maltase). It is unique because it is also a lysosomal storage disorder, leading to glycogen accumulation in the heart and skeletal muscles. * **Anderson Disease (GSD Type IV):** Caused by a deficiency of the **Branching enzyme**. This leads to the formation of abnormal glycogen with long outer chains (amylopectin-like), which triggers an immune response leading to liver cirrhosis. * **Hers Disease (GSD Type VI):** Caused by a deficiency of **Liver Phosphorylase**. This results in the inability to break down glycogen in the liver, leading to hepatomegaly and mild hypoglycemia. **2. Clinical Pearls for NEET-PG:** * **Von Gierke Disease (Type I):** Most common GSD; deficiency of Glucose-6-Phosphatase. Presents with severe hypoglycemia, lactic acidosis, and hyperuricemia. * **Cori Disease (Type III):** Deficiency of Debranching enzyme; presents with milder hypoglycemia than Type I. * **McArdle Disease (Type V):** Deficiency of Muscle Phosphorylase; presents with exercise-induced cramps and myoglobinuria. * **Mnemonic for Types I-VI:** "**V**on **P**ompe **C**orrects **A**nderson's **M**uscular **H**ers" (Von Gierke, Pompe, Cori, Anderson, McArdle, Hers). **Conclusion:** Since Pompe, Anderson, and Hers are all recognized types of GSDs, the correct answer is "All of the above."

Q: Which one of the following human tissues contains the greatest amount of body glycogen?

Skeletal muscle. **Explanation:** The correct answer is **Skeletal muscle**. This question hinges on the distinction between **concentration** (percentage per gram of tissue) and **total content** (total mass in the body). 1. **Why Skeletal Muscle is Correct:** While the liver has a higher *concentration* of glycogen (approx. 5–8% of its weight), the total mass of skeletal muscle in the human body is significantly larger (approx. 40% of body weight). Consequently, skeletal muscle stores about **three-quarters (approx. 400g)** of the body's total glycogen, whereas the liver stores only about **one-quarter (approx. 100g)**. 2. **Why Other Options are Incorrect:** * **Liver:** It has the highest *density/concentration* of glycogen, but its smaller total organ mass means it holds less total glycogen than the muscular system. * **Kidney & Cardiac Muscle:** These tissues store only negligible amounts of glycogen for local, emergency metabolic needs. They do not serve as systemic reservoirs. **High-Yield NEET-PG Pearls:** * **Function:** Liver glycogen maintains **blood glucose levels** during fasting (via Glucose-6-Phosphatase). Muscle glycogen is used **locally** for ATP production during contraction because muscles lack Glucose-6-Phosphatase and cannot release glucose into the blood. * **Regulation:** Muscle glycogen is stimulated by **epinephrine** and calcium ions, while liver glycogen is primarily regulated by **glucagon** and insulin. * **Glycogen Storage Diseases (GSD):** Type I (Von Gierke’s) affects the liver; Type II (Pompe) and Type V (McArdle) primarily affect the muscles.

Q: Which one of the following helps in generating oxygen burst in the neutrophils?

NADPH oxidase. ### Explanation **Correct Option: A. NADPH oxidase** The "Oxygen Burst" (or Respiratory Burst) is a critical process in neutrophils and macrophages used to kill phagocytosed bacteria. When a pathogen is ingested, there is a rapid increase in oxygen consumption. The enzyme **NADPH oxidase**, located in the phagosomal membrane, catalyzes the conversion of molecular oxygen ($O_2$) into **superoxide radicals** ($O_2^-$) by transferring an electron from NADPH. This superoxide is the precursor for other potent reactive oxygen species (ROS) like hydrogen peroxide and hypochlorite, which destroy the microbe. **Analysis of Incorrect Options:** * **B. Superoxide dismutase (SOD):** This enzyme actually acts as an antioxidant. It converts the superoxide radical ($O_2^-$) into hydrogen peroxide ($H_2O_2$). While it is part of the pathway, it is not the *generator* of the burst; it processes the product of NADPH oxidase. * **C. Catalase:** This is a protective enzyme that breaks down hydrogen peroxide into water and oxygen. It prevents cellular damage from ROS rather than generating the burst. * **D. Glutathione peroxidase:** This enzyme reduces hydrogen peroxide to water using reduced glutathione. It is a key component of the cellular antioxidant defense system, not the pro-oxidant burst mechanism. **Clinical Pearls for NEET-PG:** * **Chronic Granulomatous Disease (CGD):** A high-yield clinical correlation. It is caused by a genetic deficiency in **NADPH oxidase**. Patients suffer from recurrent infections with **catalase-positive** organisms (e.g., *S. aureus*, *Aspergillus*) because they cannot generate their own oxygen burst. * **MPO (Myeloperoxidase):** This enzyme uses the $H_2O_2$ produced during the burst to create **HOCl (Hypochlorous acid/Bleach)**, which is the most potent bactericidal agent in neutrophils. * **Nitroblue Tetrazolium (NBT) Test:** Used to diagnose CGD; a positive result (blue color) indicates functional NADPH oxidase.

Q: What syndrome is associated with the deficiency of Dermatan sulfate, heparan sulfate, chondroitin 4-sulfate, and chondroitin 6-sulfate?

Sly syndrome. ### Explanation **Correct Answer: C. Sly syndrome** **Underlying Medical Concept:** Sly syndrome (Mucopolysaccharidosis type VII) is caused by a deficiency of the enzyme **β-glucuronidase**. This specific enzyme is required for the degradation of glucuronic acid residues found in multiple glycosaminoglycans (GAGs). Because glucuronic acid is a common constituent of **Dermatan sulfate, Heparan sulfate, and Chondroitin 4/6-sulfates**, a deficiency in β-glucuronidase leads to the systemic accumulation of all four substances. This distinguishes it from other MPS types which typically involve only one or two GAGs. **Analysis of Incorrect Options:** * **A. Hunter syndrome (MPS II):** Caused by a deficiency of **Iduronate sulfatase**. It leads to the accumulation of **Dermatan sulfate and Heparan sulfate** only. (Key NEET-PG fact: It is X-linked recessive and lacks corneal clouding). * **B. Morquio syndrome B (MPS IVB):** Caused by a deficiency of **β-galactosidase**. It primarily results in the accumulation of **Keratan sulfate**. * **D. Hurler syndrome (MPS IH):** Caused by a deficiency of **α-L-iduronidase**. Like Hunter syndrome, it leads to the accumulation of **Dermatan sulfate and Heparan sulfate**, but presents with more severe features and corneal clouding. **High-Yield Clinical Pearls for NEET-PG:** * **Sly Syndrome Unique Feature:** It is the only MPS that can present as **Hydrops fetalis** in utero. * **GAG Triad:** If a question mentions the accumulation of **Chondroitin sulfates** alongside Dermatan and Heparan, always think of **Sly Syndrome**. * **Enzyme Mnemonic:** "Sly (7) Glucuronidase" — MPS **VII** is **β-glucuronidase** deficiency.

Q: Muscle cannot participate in gluconeogenesis due to the absence of which enzyme?

Glucose 6 phosphatase. **Explanation:** The primary goal of gluconeogenesis is to maintain blood glucose levels during fasting. While the liver (and to a lesser extent, the kidney) can perform this task, skeletal muscle cannot. **Why Glucose-6-Phosphatase is the Correct Answer:** Gluconeogenesis involves the synthesis of glucose from non-carbohydrate precursors. The final step of this pathway is the conversion of **Glucose-6-Phosphate to free Glucose**. This reaction is catalyzed by the enzyme **Glucose-6-Phosphatase**. Skeletal muscle lacks this enzyme; therefore, even though muscle can break down glycogen to Glucose-6-Phosphate, it cannot dephosphorylate it to release free glucose into the bloodstream. Instead, the Glucose-6-Phosphate enters the glycolytic pathway to provide energy (ATP) for muscle contraction. **Why the Other Options are Incorrect:** * **Enolase:** This is a reversible enzyme used in both glycolysis and gluconeogenesis. It is present in almost all tissues, including muscle. * **Pyruvate Kinase:** This is a key regulatory enzyme of glycolysis. While it is bypassed during gluconeogenesis (by Pyruvate Carboxylase and PEP Carboxykinase), its presence or absence does not define a tissue's ability to perform gluconeogenesis. **High-Yield Clinical Pearls for NEET-PG:** * **The Cori Cycle:** Since muscle cannot release glucose, it exports **Lactate** to the liver. The liver then converts lactate back to glucose via gluconeogenesis and sends it back to the muscle. * **Von Gierke’s Disease (GSD Type I):** This condition is caused by a deficiency of Glucose-6-Phosphatase. It leads to severe fasting hypoglycemia because neither glycogenolysis nor gluconeogenesis can release glucose from the liver. * **Key Gluconeogenic Organs:** Liver (90%) and Kidney (10%). During prolonged starvation, the kidney's contribution increases significantly.

Q: Amino sugars are formed from which of the following precursors?

Fructose-6-phosphate. ### Explanation The synthesis of amino sugars (hexosamines) occurs via the **Hexosamine Biosynthetic Pathway (HBP)**. **1. Why Fructose-6-phosphate is correct:** The key rate-limiting step in the formation of amino sugars is the conversion of **Fructose-6-phosphate (F6P)** into **Glucosamine-6-phosphate**. This reaction is catalyzed by the enzyme **Glutamine-fructose-6-phosphate amidotransferase (GFAT)**. In this process, an amino group is transferred from the donor amino acid, **Glutamine**, to Fructose-6-phosphate. Glucosamine-6-phosphate then serves as the precursor for N-acetylglucosamine (GlcNAc), N-acetylgalactosamine (GalNAc), and sialic acids, which are essential components of glycoproteins, glycolipids, and glycosaminoglycans (GAGs). **2. Why the other options are incorrect:** * **Glucose-6-phosphate (B):** While G6P is the starting point of glycolysis and the HMP shunt, it must first be isomerized to Fructose-6-phosphate by phosphohexose isomerase before it can enter the hexosamine pathway. * **Glucose-1-phosphate (A):** This is primarily involved in glycogenesis (glycogen synthesis) and uronic acid pathways, not direct amino sugar formation. * **Fructose-1-phosphate (C):** This is an intermediate of fructose metabolism in the liver (via fructokinase) and does not serve as a substrate for GFAT. ### High-Yield Clinical Pearls for NEET-PG: * **Nitrogen Donor:** Glutamine is the obligatory nitrogen donor for amino sugar synthesis. * **Feedback Inhibition:** The end product, UDP-GlcNAc, inhibits the rate-limiting enzyme GFAT. * **Clinical Significance:** The hexosamine pathway is linked to **insulin resistance**. High intracellular glucose levels increase flux through this pathway, leading to the modification of signaling proteins (O-GlcNAcylation), which can impair insulin sensitivity. * **Essential Amino Sugars:** Glucosamine, Galactosamine, and N-acetylneuraminic acid (NANA/Sialic acid).

Question 1

ATP is an allosteric regulator of which enzymes?

Accepted Answer

PFK 1 and Pyruvate kinase

Answer

Hexokinase and PFK 1

Answer

PFK 1 and PFK 2

Answer

Glyceraldehyde 3 phosphate dehydrogenase and PFK 1

Question 2

Which of the following hormones stimulates glucose utilization?

Accepted Answer

Insulin

Answer

Growth hormone

Answer

Corticosteroid

Answer

Glucagon

Question 3

All of the following are glycogen storage disorders except?

Accepted Answer

All of the above

Answer

Pompe disease

Answer

Hers disease

Answer

Anderson disease

Question 4

Which one of the following human tissues contains the greatest amount of body glycogen?

Accepted Answer

Skeletal muscle

Answer

Liver

Answer

Kidney

Answer

Cardiac muscle

Question 5

Which one of the following helps in generating oxygen burst in the neutrophils?

Accepted Answer

NADPH oxidase

Answer

Superoxide dismutase

Answer

Catalase

Answer

Glutathione peroxidase

Question 6

What syndrome is associated with the deficiency of Dermatan sulfate, heparan sulfate, chondroitin 4-sulfate, and chondroitin 6-sulfate?

Accepted Answer

Sly syndrome

Answer

Hunter syndrome

Answer

Morquio syndrome B

Answer

Hurler syndrome

Question 7

Muscle cannot participate in gluconeogenesis due to the absence of which enzyme?

Accepted Answer

Glucose 6 phosphatase

Answer

Enolase

Answer

Pyruvate kinase

Answer

All of the above

Question 8

Amino sugars are formed from which of the following precursors?

Accepted Answer

Fructose-6-phosphate

Answer

Glucose-1-phosphate

Answer

Glucose-6-phosphate

Answer

Fructose-1-phosphate

Question 9

An 8-day-old child presents with yellow sclera, whitish stool, and turmeric-colored urine on the 3rd day of septicemia treated with broad-spectrum antibiotics. What is the likely diagnosis?

Accepted Answer

Galactose-1-phosphate uridyltransferase deficiency

Answer

Galactosidase deficiency

Answer

Ammonia toxicity

Answer

All of the above

Question 10

What are the final products of the Hexose Monophosphate Pathway?

Accepted Answer

6 NADPH

Answer

2 NADPH

Answer

3 NADPH

Answer

Variable

Carbohydrate Metabolism — MCQs

Carbohydrate Metabolism — MCQs

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