NEET-PG 2015 Practice Questions

Q: Which type of glial cell is derived from mesodermal origin?

Microglial cells. ***Microglial cells*** - **Microglial cells** are unique among glial cells as they originate from **mesoderm**, specifically from **monocyte/macrophage precursors** in the bone marrow [1]. - They function as the **immune cells of the central nervous system (CNS)**, scavenging for plaques, damaged neurons, and infectious agents [1]. *Macroglial cells* - This is a broad category that includes **astrocytes, oligodendrocytes, and ependymal cells**, all of which are derived from **neuroectoderm**, not mesoderm [1]. - They perform various supportive roles but are distinct in origin from microglial cells [1]. *Oligodendrocytes* - **Oligodendrocytes** are derived from **neuroectoderm** and are responsible for forming the **myelin sheath** around axons in the CNS [2]. - Myelination is crucial for rapid and efficient nerve impulse conduction. *Ependymal cells* - **Ependymal cells** are derived from **neuroectoderm** and line the **ventricles of the brain** and the **central canal of the spinal cord**. - They play a role in the production and circulation of **cerebrospinal fluid (CSF)**.

Q: In the context of energy metabolism, which coenzyme is niacin a precursor to?

NAD. ***NAD*** - Niacin (vitamin B3) is a direct precursor to **nicotinamide adenine dinucleotide (NAD/NAD+)**. - NAD is the crucial coenzyme in **energy metabolism**, primarily involved in **catabolic pathways** such as glycolysis, TCA cycle, and electron transport chain. - Functions as an **electron carrier** in redox reactions, accepting electrons during oxidation of fuel molecules. *Thiamine pyrophosphate (TPP)* - **Thiamine (vitamin B1)** is the precursor to TPP, not niacin. - TPP plays a vital role in **carbohydrate metabolism**, particularly in pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase complexes. *NADP* - While niacin is also a precursor to **NADP/NADPH**, this coenzyme is primarily used in **anabolic (biosynthetic) pathways**, not energy metabolism. - NADP functions in reductive biosynthesis (fatty acid synthesis, cholesterol synthesis) and **oxidative stress protection** via the pentose phosphate pathway. - The question specifically asks about **energy metabolism**, making NAD the correct answer as it participates in catabolic, energy-producing reactions. *Flavin adenine dinucleotide (FAD)* - **Riboflavin (vitamin B2)** is the precursor to FAD, not niacin. - FAD is a coenzyme involved in various metabolic reactions, especially in the **TCA cycle** and **electron transport chain**, acting as an electron acceptor.

Q: How many molecules of Acetyl CoA are produced from β-oxidation of palmitic acid?

8 acetyl CoA. ***8 acetyl CoA*** - Palmitic acid is a **16-carbon saturated fatty acid (C16:0)**. During β-oxidation, each cycle cleaves two carbons as **acetyl CoA**. - The formula for acetyl CoA produced is **n/2**, where n = number of carbons. For palmitic acid: 16/2 = **8 acetyl CoA molecules**. - Alternatively: Palmitic acid undergoes **7 cycles of β-oxidation** [(n/2) - 1 = 7], each producing 1 acetyl CoA (7 total), plus the final 2-carbon fragment forming the 8th acetyl CoA. *3 acetyl CoA* - This number is too low for a 16-carbon fatty acid. **Short-chain fatty acids** would produce fewer acetyl CoA molecules. - This value corresponds to β-oxidation of a **6-carbon fatty acid** (hexanoic acid), not palmitic acid. *6 acetyl CoA* - This number is also too low for a 16-carbon fatty acid. - This quantity would be produced from a **12-carbon fatty acid** (lauric acid), not palmitic acid. *16 Acetyl CoA* - This number is too high and would incorrectly imply that each carbon forms an acetyl CoA independently. - Sixteen acetyl CoA molecules would be produced from a **32-carbon fatty acid**, which is extremely rare in biological systems.

Q: Which of the following is not a metabolic product of the urea cycle?

Alanine. ***Alanine*** - **Alanine** is an amino acid primarily involved in the **glucose-alanine cycle** for glucose production and ammonia transport, not as a direct metabolic product within the urea cycle. - While it plays a role in nitrogen metabolism, it is not synthesized or directly consumed as an intermediate in the reactions that convert ammonia to urea. *Citrulline* - **Citrulline** is a key intermediate formed during the second step of the urea cycle when **ornithine carbamoyltransferase** combines carbamoyl phosphate with ornithine. - It is then transported out of the mitochondrion into the cytosol to continue the cycle. *Ornithine* - **Ornithine** is an amino acid that acts as a **catalytic intermediate** in the urea cycle, being regenerated at the end of the cycle to combine with carbamoyl phosphate. - It does not directly contribute a nitrogen atom to urea but is essential for the cycle's continuation. *Arginine* - **Arginine** is an amino acid that is a direct precursor to urea in the penultimate step of the urea cycle, where **arginase** cleaves it into urea and ornithine. - It provides one of the nitrogen atoms and the carbon atom for the formation of urea.

Q: What primarily forms the core of chylomicrons?

Triglycerides. ***Triglycerides*** - Chylomicrons are primarily responsible for transporting **dietary triglycerides** from the intestines to other tissues. - Their large core, composed mainly of **triglycerides**, allows efficient transport of these hydrophobic molecules. *Triglycerides and Cholesterol together* - While **cholesterol** is present in chylomicrons, it is less abundant than **triglycerides** and primarily exists as **cholesterol esters** in the core. - The core is not an equal mixture; **triglycerides** overwhelmingly dominate the volume. *Free fatty acids* - **Free fatty acids** are transported in the blood primarily bound to **albumin**, not within the core of chylomicrons. - Chylomicrons typically carry **esterified fatty acids** as part of triglycerides. *Triglyceride, Cholesterol and Phospholipids* - **Phospholipids** form the outer monolayer of the chylomicron, along with apoproteins, making them **amphipathic**. - They do not constitute a core component but rather the **surface interface** with the aqueous environment.

Q: Boiled cabbage or rancid butter smelling urine is seen in

Isovaleric Acidaemia. ***Isovaleric Acidaemia*** - **Boiled cabbage or rancid butter odor** in urine is a classic feature of isovaleric acidemia, caused by the accumulation of isovaleric acid. - This **inborn error of metabolism** affects **leucine metabolism** due to deficiency of isovaleryl-CoA dehydrogenase. *Tyrosinemia* - Does NOT present with boiled cabbage or rancid butter odor. The characteristic features are **liver dysfunction** and **renal tubular defects**. - Tyrosinemia Type I is caused by deficiency of **fumarylacetoacetate hydrolase**, leading to accumulation of tyrosine metabolites. *Phenylketonuria* - Characterized by a **mousy or musty odor** in urine, resulting from the accumulation of phenylacetic acid. - The defect is in the enzyme **phenylalanine hydroxylase**, not associated with boiled cabbage odor. *Multiple carboxylase deficiency* - Typically presents with a **"cat urine" smell** due to the accumulation of various organic acids. - The deficiency impairs the function of several **biotin-dependent carboxylases**, not specifically linked to the boiled cabbage odor.

Q: Apo B48 is synthesized in -

Intestine. ***Intestine*** - **Apo B48** is a truncated form of apolipoprotein B-100, uniquely synthesized in the **intestine** through RNA editing. - It is a crucial structural component of **chylomicrons**, which are lipoprotein particles responsible for transporting exogenous dietary lipids from the intestine to other tissues. *Liver* - The liver primarily synthesizes **Apo B100**, which is a full-length apolipoprotein B and a major component of VLDL, IDL, and LDL. - It does not produce Apo B48. *Kidney* - The kidneys are involved in filtering waste products and regulating fluid balance, but they do not play a role in the synthesis of apolipoproteins like Apo B48. - Kidney cells are not equipped with the specific machinery for Apo B mRNA editing. *RBCs* - Red blood cells (RBCs) are primarily responsible for oxygen transport and lack a nucleus and most organelles, including those required for protein synthesis. - Therefore, RBCs cannot synthesize proteins such as Apo B48.

Q: What is the end product of purine metabolism in most mammals?

Allantoin. ***Allantoin*** - **Allantoin** is the primary end product of **purine metabolism** in **most mammals** (except humans and higher primates), formed by the oxidation of uric acid by the enzyme **uricase**. - This conversion makes purine waste products more **water-soluble** and easier to excrete via the kidneys. - **Important clinical note:** Humans lack functional uricase, so **uric acid** is the end product in humans; this distinction is why hyperuricemia and gout occur in humans but not in most other mammals. *Glycogen* - **Glycogen** is a complex carbohydrate and serves as a primary **energy storage molecule** in animals, derived from glucose metabolism, not purine catabolism. - Its metabolism is regulated by hormones like **insulin** and **glucagon**, involved in maintaining blood glucose levels. *Pyrimidine* - **Pyrimidine** is a type of nitrogenous base, structurally distinct from purines, and is a component of DNA and RNA, not an end product of purine catabolism. - **Pyrimidine metabolism** involves the synthesis and breakdown of bases like cytosine, thymine, and uracil, which follows a separate biochemical pathway. *Histidine* - **Histidine** is an **essential amino acid**, a building block of proteins, and is involved in various metabolic processes, including histamine synthesis. - It plays no role as an end product of purine degradation; rather, its own metabolism leads to products like **urocanic acid**.

Q: Abnormal proteins which are bound to ubiquitin are degraded in -

Proteasomes. ***Proteasomes*** - **Proteasomes** are multi-subunit protein complexes responsible for degrading **ubiquitin-tagged proteins**. - This degradation is a tightly regulated process essential for cell cycle control, gene expression, and immune response. *Golgi apparatus* - The **Golgi apparatus** primarily functions in modifying, sorting, and packaging proteins and lipids synthesized in the Endoplasmic Reticulum. - It does not directly participate in the degradation of **ubiquitin-bound proteins**. *Smooth ER* - The **smooth endoplasmic reticulum (SER)** is involved in lipid synthesis, detoxification of drugs and poisons, and storage of calcium ions. - It lacks ribosomes and is not directly implicated in the degradation of misfolded proteins tagged with ubiquitin. *Lysosomes* - **Lysosomes** are organelles containing various hydrolytic enzymes that break down waste materials and cellular debris, as well as foreign invaders like bacteria. - While they degrade proteins, they primarily target **extracellular proteins** taken up by endocytosis or cellular components via **autophagy**, not specifically ubiquitin-bound proteins.

Question 1

Which type of glial cell is derived from mesodermal origin?

Accepted Answer

Microglial cells

Answer

Macroglial cells

Answer

Oligodendrocytes

Answer

Ependymal cells

Question 2

In the context of energy metabolism, which coenzyme is niacin a precursor to?

Accepted Answer

NAD

Answer

Thiamine pyrophosphate (TPP)

Answer

NADP

Answer

Flavin adenine dinucleotide (FAD)

Question 3

How many molecules of Acetyl CoA are produced from β-oxidation of palmitic acid?

Accepted Answer

8 acetyl CoA

Answer

3 acetyl CoA

Answer

16 Acetyl CoA

Answer

6 acetyl CoA

Question 4

Which of the following is not a metabolic product of the urea cycle?

Accepted Answer

Alanine

Answer

Citrulline

Answer

Arginine

Answer

Ornithine

Question 5

What primarily forms the core of chylomicrons?

Accepted Answer

Triglycerides

Answer

Triglycerides and Cholesterol together

Answer

Free fatty acids

Answer

Triglyceride, Cholesterol and Phospholipids

Question 6

Boiled cabbage or rancid butter smelling urine is seen in

Accepted Answer

Isovaleric Acidaemia

Answer

Tyrosinemia

Answer

Phenylketonuria

Answer

Multiple carboxylase deficiency

Question 7

Apo B48 is synthesized in -

Accepted Answer

Intestine

Answer

Liver

Answer

Kidney

Answer

RBCs

Question 8

What is the end product of purine metabolism in most mammals?

Accepted Answer

Allantoin

Answer

Glycogen

Answer

Pyrimidine

Answer

Histidine

Question 9

Abnormal proteins which are bound to ubiquitin are degraded in -

Accepted Answer

Proteasomes

Answer

Golgi apparatus

Answer

Smooth ER

Answer

Lysosomes

Question 10

Which of the following statements about Niemann-Pick disease is false?

Accepted Answer

Type B Niemann-Pick disease is characterized by severe neurological symptoms.

Answer

Due to deficiency of sphingomyelinase.

Answer

CNS symptoms are present in type A.

Answer

Histiocytes show PAS positive inclusions, and Type A is more severe.

NEET-PG 2015

Anatomy

Biochemistry

Pathology