NEET-PG 2013 Practice Questions

Q: Which of the following plant components is not fermented by gastrointestinal microorganisms?

Lignin. ***Lignin*** - **Lignin** is a complex polymer found in plant cell walls that is highly resistant to degradation by digestive enzymes and microbial fermentation in the gastrointestinal tract. - Its complex, cross-linked structure makes it **non-fermentable** by the microorganisms typically present in the human gut. *Cellulose* - **Cellulose** is a major component of plant cell walls and is a type of dietary fiber that can be fermented by certain gut bacteria. - While humans lack the enzymes to digest cellulose, colonic microorganisms possess cellulases that break it down into **short-chain fatty acids (SCFAs)**. *Hemicellulose* - **Hemicellulose** is a diverse group of plant polysaccharides that are a significant source of fermentable fiber for gut microbiota. - It is readily broken down by gastrointestinal bacteria into **SCFAs** and gases, contributing to colonic health. *Pectin* - **Pectin** is a soluble dietary fiber found in fruits and vegetables, known for its gel-forming properties. - It is highly fermentable by gut microorganisms, leading to the production of **SCFAs** like butyrate, propionate, and acetate.

Q: Trypsinogen is converted to trypsin by?

Removal of specific amino acids from trypsinogen. ***Removal of specific amino acids from trypsinogen*** - Trypsinogen is an **inactive zymogen** that is activated by the enzymatic cleavage of a **short N-terminal peptide**. - This cleavage event, primarily catalyzed by **enteropeptidase** (or trypsin itself), transforms trypsinogen into active **trypsin**, a process known as **proteolytic activation**. *Combination of 2 molecules of trypsinogen* - The activation of trypsinogen to trypsin is a **unimolecular conformational change** followed by proteolytic cleavage, not a combination reaction between two zymogen molecules. - While trypsin can activate other trypsinogen molecules, the initial activation does not involve the physical combination of two zymogen molecules. *Phosphorylation* - **Phosphorylation** is a common regulatory mechanism in proteins but is not the primary method for activating inactive trypsinogen. - Trypsinogen activation relies on a **proteolytic cleavage event**, rather than the addition of a phosphate group. *Addition of alkyl group* - The addition of an **alkyl group** is not a known mechanism for the physiological activation of trypsinogen. - Enzymatic activation typically involves **hydrolysis of peptide bonds** or other specific post-translational modifications.

Q: What is the primary reason for the detergent action of bile salts?

Amphipathic nature. ***Amphipathic nature*** - Bile salts are **amphipathic molecules**, meaning they have both **hydrophilic (water-loving)** and **hydrophobic (water-fearing)** regions. - This dual nature allows them to emulsify fats by surrounding lipid droplets with their hydrophobic ends dissolving in the fat and their hydrophilic ends facing the aqueous environment, stabilizing the emulsion. *Hydrophobic properties* - While bile salts do possess **hydrophobic regions**, these alone are not sufficient for detergent action. - The ability to interact with both oil and water phases simultaneously is crucial for their role in **emulsification**. *Acts as a zwitterion* - A zwitterion is a molecule with both a **positive and negative charge**, but an overall neutral charge. - This property is not the primary mechanism behind the **detergent action** of bile salts, which relies more on their ability to solubilize fats. *None of the options* - The **amphipathic nature** is indeed the primary reason for the detergent action; therefore, this option is incorrect.

Q: Which of the following is a natural uncoupler found in brown adipose tissue?

Thermogenin. ***Correct: Thermogenin*** - Also known as **uncoupling protein 1 (UCP1)**, it is a **mitochondrial inner membrane protein** naturally expressed in **brown adipose tissue** - Thermogenin creates a **proton leak** across the inner mitochondrial membrane, bypassing ATP synthase and dissipating the proton gradient as heat, thereby mediating **non-shivering thermogenesis** - This is the only natural uncoupler among the options listed *Incorrect: 2,4-Nitrophenol* - This compound is **not a naturally occurring uncoupler** in mammalian tissues - While it can act as a synthetic uncoupler in laboratory settings, it is not found in biological systems *Incorrect: 2,4-Dinitrophenol* - This is a well-known **synthetic chemical uncoupler** of oxidative phosphorylation, historically used as a weight-loss drug (now banned due to toxicity) - It works by carrying protons across the inner mitochondrial membrane, but it is **not a natural biological molecule** found in the body *Incorrect: Oligomycin* - Oligomycin is an **inhibitor of ATP synthase (Complex V)**, not an uncoupler - It binds to the F0 subunit of ATP synthase, blocking the flow of protons through the enzyme and thereby preventing ATP synthesis - This blocks both the proton gradient dissipation AND ATP production, which is mechanistically different from uncoupling

Q: Peliosis hepatis is caused by all except?

Analgesics. ***Analgesics*** - While various drugs can cause liver injury, **analgesics** are not typically associated with the development of **peliosis hepatis**. [1] - **Peliosis hepatis** involves blood-filled cysts in the liver and is linked to specific agents, not common pain relievers. *Anabolic steroids* - **Anabolic steroids** are a well-known cause of **peliosis hepatis**, especially with prolonged high-dose use. - They can induce sinusoidal dilation and hemorrhage, leading to **blood-filled cysts** in the liver. *OC pills* - **Oral contraceptive pills** (OCPs) containing estrogen have been implicated in the development of **peliosis hepatis**, though it is rare. - The estrogen component is thought to affect the **vascular endothelium** and sinusoidal integrity of the liver. *Danazol* - **Danazol**, an attenuated androgen, is strongly associated with **peliosis hepatis** and other liver complications. - It can cause severe damage to the **hepatic sinusoids**, leading to the characteristic blood-filled cavities. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Liver and Gallbladder, pp. 847-848.

Q: Daily salivary secretion is

1000-1500 ml. ***1000-1500 ml*** - The average daily salivary secretion in healthy adults ranges from **1000 to 1500 ml**, with variations depending on individual factors and stimulation. - This volume is crucial for various functions, including **digestion**, oral hygiene, and speech. *1500-2000 ml* - This range is generally considered to be on the **higher side** of normal daily salivary output, exceeding the typical average. - While individual variations exist, consistent secretion at this level might suggest **hypersecretion** or ptyalism in some cases. *More than 2000 ml* - Daily salivary secretion **rarely exceeds 2000 ml** in healthy individuals. - Such high volumes could indicate a pathological condition leading to **sialorrhea** or excessive salivation. *Less than 1000 ml* - A daily salivary secretion of **less than 1000 ml** is often indicative of **hyposalivation** or dry mouth (xerostomia). - This reduced volume can lead to problems with chewing, swallowing, speaking, and an increased risk of dental caries.

Q: Sugars are primarily absorbed in?

Jejunum. ***Jejunum*** - The **jejunum** is the primary site for the absorption of most digested nutrients, including the vast majority of **monosaccharides** (simple sugars like glucose, fructose, and galactose). - Its structure, with numerous **plicae circulares**, villi, and microvilli, provides a large surface area optimized for efficient nutrient uptake. *Duodenum* - The **duodenum** is mainly involved in the **chemical digestion** of food, receiving chyme from the stomach and mixing it with digestive enzymes from the pancreas and bile from the liver. - While some minimal absorption can occur, it is not the primary site for extensive sugar absorption. *Ileum* - The **ileum** is mainly responsible for the absorption of **vitamin B12** and **bile salts**. - Although some residual nutrient absorption can happen here if the jejunum is compromised, it is not the primary physiological site for sugar absorption. *Ascending colon* - The **ascending colon** is primarily involved in the absorption of **water and electrolytes**, forming solid stool. - It does not significantly absorb sugars; undigested carbohydrates reaching the colon are typically fermented by gut bacteria.

Q: Lowest pH is seen in which of the gastrointestinal secretions?

Gastric juice. ***Gastric juice*** - Gastric juice contains **hydrochloric acid (HCl)**, secreted by parietal cells, which gives it a very **low pH (1.5-3.5)**. - This acidic environment is crucial for protein digestion by **pepsin** and for killing ingested microorganisms. *Bile juice* - Bile juice is typically **alkaline**, with a pH ranging from **7.6 to 8.6**. - Its primary role is to **emulsify fats** in the small intestine, and it does not contain significant acidic components. *Saliva* - Saliva has a relatively neutral pH, typically ranging from **6.2 to 7.6**. - It contains enzymes like **amylase** and **lipase** for initial carbohydrate and lipid digestion, but no strong acids. *Pancreatic juice* - Pancreatic juice is highly **alkaline**, with a pH usually between **8.0 and 8.3**, due to its high concentration of bicarbonate. - This alkalinity neutralizes the acidic chyme entering the duodenum from the stomach, creating an optimal environment for pancreatic enzymes.

Q: Inhibition of myenteric plexus results in

Decreased gut motility. ***Decreased gut motility*** - The **myenteric plexus** (Auerbach's plexus) is primarily responsible for regulating **gastrointestinal motility**, including peristalsis and muscle contraction. - Its inhibition would therefore lead to **reduced peristaltic movements** and **decreased gut motility**. *Hyperacidity* - **Gastric acid secretion** is mainly regulated by the vagus nerve (via acetylcholine), gastrin, and histamine, not directly by the myenteric plexus. - While gut motility can indirectly affect acid exposure, a primary and direct consequence of myenteric plexus inhibition is not hyperacidity. *Diarrhea* - **Diarrhea** is typically caused by increased gut motility, increased secretion, or decreased absorption. - Inhibition of the myenteric plexus would lead to **decreased motility**, making diarrhea an unlikely outcome. *Increased secretions* - **Gastrointestinal secretions** are largely controlled by the submucosal plexus (Meissner's plexus) and hormonal factors. - While the myenteric plexus has some indirect influence, its primary role is motility, and its inhibition would not directly lead to increased secretions.

Question 1

Which of the following plant components is not fermented by gastrointestinal microorganisms?

Accepted Answer

Lignin

Answer

Cellulose

Answer

Hemicellulose

Answer

Pectin

Question 2

Trypsinogen is converted to trypsin by?

Accepted Answer

Removal of specific amino acids from trypsinogen

Answer

Combination of 2 molecules of trypsinogen

Answer

Phosphorylation

Answer

Addition of alkyl group

Question 3

What is the primary reason for the detergent action of bile salts?

Accepted Answer

Amphipathic nature

Answer

Hydrophobic properties

Answer

Acts as a zwitterion

Answer

None of the options

Question 4

Which of the following is a natural uncoupler found in brown adipose tissue?

Accepted Answer

Thermogenin

Answer

2,4-Nitrophenol

Answer

2,4-Dinitrophenol

Answer

Oligomycin

Question 5

Dystrophic calcification is seen in

Accepted Answer

Atheromatous plaque

Answer

Vitamin A intoxication

Answer

Milk alkali syndrome

Answer

Hyperparathyroidism

Question 6

Peliosis hepatis is caused by all except?

Accepted Answer

Analgesics

Answer

OC pills

Answer

Danazol

Answer

Anabolic steroids

Question 7

Daily salivary secretion is

Accepted Answer

1000-1500 ml

Answer

1500-2000 ml

Answer

More than 2000 ml

Answer

Less than 1000 ml

Question 8

Sugars are primarily absorbed in?

Accepted Answer

Jejunum

Answer

Duodenum

Answer

Ascending colon

Answer

Ileum

Question 9

Lowest pH is seen in which of the gastrointestinal secretions?

Accepted Answer

Gastric juice

Answer

Bile juice

Answer

Saliva

Answer

Pancreatic juice

Question 10

Inhibition of myenteric plexus results in

Accepted Answer

Decreased gut motility

Answer

Hyperacidity

Answer

Diarrhea

Answer

Increased secretions

NEET-PG 2013

Biochemistry

Pathology

Physiology