NEET-PG 2013 Practice Questions

Q: Which enzyme catalyzes oxidative deamination?

Glutamate dehydrogenase. ***Glutamate dehydrogenase*** - This enzyme catalyzes the conversion of **glutamate** to **α-ketoglutarate** and ammonia (NH₃), which is an oxidative deamination reaction. - It utilizes **NAD⁺ or NADP⁺** as a coenzyme to remove hydrogen atoms during the oxidation process. - Plays a crucial role in both **amino acid catabolism** and anabolism. *Glutaminase* - This enzyme hydrolyzes **glutamine** to glutamate and ammonia, which is a **hydrolytic deamidation** reaction, not an oxidative deamination. - It does not involve the oxidation of the substrate or require NAD⁺/NADP⁺ as cofactors. *Glutamine synthase* - This enzyme synthesizes **glutamine** from glutamate and ammonia, using ATP, which is a **biosynthetic** reaction, not a catabolic deamination. - It is involved in **ammonia detoxification** and amino acid synthesis, functioning in the opposite direction of deamination. *None of the options* - This option is incorrect because **glutamate dehydrogenase** is a valid correct answer. - Glutamate dehydrogenase is the primary enzyme responsible for oxidative deamination in human metabolism.

Q: Hereditary orotic aciduria Type-I is due to deficiency of?

UMP synthase. ***UMP synthase*** - Hereditary orotic aciduria Type-I is caused by a deficiency of the **bifunctional enzyme UMP synthase** (also called UMP synthase complex). - UMP synthase catalyzes two sequential reactions in the *de novo* pyrimidine synthesis pathway: 1. **OPRT activity**: Converts orotate → orotidine 5'-monophosphate (OMP) 2. **ODC activity**: Converts OMP → uridine 5'-monophosphate (UMP) - This is the **most precise and complete answer** as it identifies the actual enzyme complex that is deficient. - **Clinical features**: Megaloblastic anemia, growth retardation, immunodeficiency; responds to oral uridine supplementation. *Orotate phosphoribosyl transferase* - This represents only **one of the two catalytic activities** of the UMP synthase enzyme (the first step). - While this activity is indeed deficient in Type-I orotic aciduria, naming only this activity is **incomplete** because the enzyme has two functions. - This would be a **partial answer** rather than the complete enzyme name. *Orotic acid decarboxylase* - This represents only **the second catalytic activity** of the UMP synthase enzyme (converts OMP to UMP). - Like OPRT, this activity is also deficient, but naming only this component is **incomplete**. - **Type II orotic aciduria** (extremely rare) involves isolated ODC deficiency without OPRT deficiency. *All of the options* - While technically both OPRT and ODC activities are affected in Type-I orotic aciduria, the **standard nomenclature** refers to the deficient enzyme as **"UMP synthase"** - the name of the complete bifunctional enzyme. - In medical terminology and examination context, we identify enzyme deficiencies by the **name of the enzyme complex**, not by listing all its individual catalytic activities. - Therefore, **"UMP synthase"** is the single most accurate and complete answer.

Q: Which of the following molecular interactions are found in the structure of DNA?

All of the options. ***All of the options*** - All three types of molecular interactions listed are present in DNA structure, making this the correct answer. - **Hydrogen bonds** hold together the two strands of the DNA double helix, forming between complementary base pairs (A-T with 2 hydrogen bonds, G-C with 3 hydrogen bonds). - **Glycosidic bonds** (N-glycosidic bonds) link the nitrogenous bases to the C1' carbon of the deoxyribose sugar in each nucleotide. - **Covalent interactions** (phosphodiester bonds) form the strong, stable sugar-phosphate backbone by linking the 3' hydroxyl group of one sugar to the 5' phosphate group of the next. *Hydrogen bond* - This is a **true statement** - hydrogen bonds are essential structural components of DNA. - However, this option alone is **incomplete** as DNA structure also contains glycosidic bonds and covalent phosphodiester bonds. - If only hydrogen bonds were present, there would be no nucleotides or backbone structure. *Glycosidic bond* - This is a **true statement** - glycosidic bonds are present in every nucleotide of DNA. - However, this option alone is **incomplete** as DNA also requires hydrogen bonds for base pairing and phosphodiester bonds for the backbone. - Without other bonds, individual nucleotides could not form a functional double helix. *Covalent interactions* - This is a **true statement** - covalent phosphodiester bonds form the DNA backbone within each strand. - However, this option alone is **incomplete** as it doesn't account for glycosidic bonds (nucleotide formation) or hydrogen bonds (strand pairing). - While the strongest bonds in DNA, they alone cannot create the complete double helix structure.

Q: What is the major fibril protein associated with Primary Amyloidosis?

Immunoglobulin Light Chain. ***AL*** - In Primary Amyloidosis, **AL amyloid** is derived from immunoglobulin light chains produced by **plasma cell dyscrasias** [1]. - This type of amyloidosis is commonly associated with conditions like **multiple myeloma** or monoclonal gammopathy [1]. *Transthyretin* - This protein is associated with **Familial Amyloid Polyneuropathy** and **Senile Systemic Amyloidosis**, not Primary Amyloidosis. - Transthyretin amyloidosis (ATTR) results from **mutations** or **aging**, contributing to different clinical presentations than AL. *AA* - AA amyloidosis is secondary and occurs due to **chronic inflammatory** conditions, such as rheumatoid arthritis or chronic infections. - It is not the main fibril protein in **Primary Amyloidosis**, which is specifically linked to **light chains**. *Procalcitonin* - Procalcitonin is a **biomarker** used primarily for diagnosing bacterial infections, particularly sepsis, and is not involved in amyloidogenesis. - It does not relate to amyloidosis and is not a component of amyloid fibrils. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. Diseases of the Immune System, pp. 266-267.

Q: Gastric carcinoma is associated with all of the following EXCEPT:

Activation of RAS. ***Activation of RAS*** - **RAS mutations** are relatively uncommon in gastric carcinoma compared to other gastrointestinal malignancies. While KRAS mutations can occur in approximately 10-15% of gastric cancers (particularly intestinal type), they are **far less frequent** than in **pancreatic adenocarcinoma** (~90%) or **colorectal carcinoma** (~40%). - In the context of gastric carcinoma, RAS pathway alterations are **not considered a major oncogenic driver** compared to the other molecular changes listed, making this the **LEAST characteristically associated** alteration. *Inactivation of p53* - **Inactivation of the p53 tumor suppressor gene** is one of the most frequent molecular events in gastric carcinoma, occurring in approximately **50-60% of cases**. - Loss of p53 function leads to genomic instability, uncontrolled cell proliferation, and resistance to apoptosis, contributing significantly to **tumorigenesis** and **poor prognosis**. *Over expression of C-met* - **Overexpression of C-MET**, a receptor tyrosine kinase for hepatocyte growth factor (HGF), is commonly observed in gastric carcinoma (30-40% of cases) and is strongly linked to **tumor growth**, **invasion**, and **metastasis**. - C-MET amplification and overexpression promote cell proliferation, survival, migration, and angiogenesis, making it an important **therapeutic target** in advanced gastric cancer. *Over expression of C-erb* - **Overexpression of C-erbB-2 (HER2/neu)** is found in approximately **10-20% of gastric adenocarcinomas**, particularly the intestinal type. - HER2 amplification or overexpression is a significant **prognostic and predictive biomarker**, and is specifically targeted by **trastuzumab** (Herceptin) therapy in HER2-positive advanced gastric cancer, improving survival outcomes.

Q: In the breast, lactiferous ducts are formed under the influence of which hormone?

Estrogen. ***Estrogen*** - **Estrogen** plays a primary role in the development and branching of the **lactiferous ducts** in the breast. - It stimulates the proliferation of ductal epithelial cells, contributing to the growth of the duct system. *Progesterone* - **Progesterone** is primarily responsible for the development of the **lobuloalveolar system** and secretory differentiation within the breast. - While essential for lactation, its main function is not duct formation but rather the maturation of secretory units. *LH* - **Luteinizing hormone (LH)** is crucial for ovulation and the formation of the **corpus luteum** in the ovaries. - It has no direct role in the structural development of the lactiferous ducts in the breast. *FSH* - **Follicle-stimulating hormone (FSH)** is essential for the growth and maturation of **ovarian follicles**. - It does not directly influence the formation or development of lactiferous ducts in the breast.

Q: Which type of nerve fibers are responsible for carrying joint position and vibration sense?

A-beta fibers. ***A-beta fibers*** - **A-beta fibers** are **large-diameter, myelinated** sensory fibers that conduct impulses rapidly. - They are primarily responsible for transmitting **light touch, pressure, joint position (proprioception), and vibration sense**. - **This is the correct answer** because A-beta fibers carry **BOTH joint position AND vibration sense together**. *A-alpha fibers* - **A-alpha fibers** are the **largest and fastest** conducting nerve fibers. - They include **motor nerves to skeletal muscles** and **sensory fibers from muscle spindles (Ia) and Golgi tendon organs (Ib)**. - While Ia fibers (A-alpha) do carry **proprioception from muscle spindles**, they do **NOT carry vibration sense**. - The question asks for fibers carrying **BOTH** joint position **AND** vibration sense, making A-beta the correct answer. *C fibers* - **C fibers** are **small-diameter, unmyelinated** nerve fibers with **slow conduction velocities**. - They are responsible for transmitting **dull, aching pain, temperature, and crude touch**. *A-delta fibers* - **A-delta fibers** are **small-diameter, thinly myelinated** nerve fibers with an intermediate conduction velocity. - They primarily transmit **sharp, fast pain** and **cold temperature sensations**.

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: Ovulation occurs how long after the LH surge peak?

12-24 hours. ***12-24 hours*** - Ovulation, the release of a mature egg from the **ovary**, typically occurs within **12 to 24 hours after the peak of the luteinizing hormone (LH) surge**. - The LH surge itself usually lasts 24 to 48 hours and is a critical signal for the final maturation and release of the oocyte. *24-48 hours* - While the **LH surge** can last up to 48 hours, **ovulation** (the actual release of the egg) generally happens more rapidly, usually within 12-24 hours of the *peak* of this surge. - This timeframe is a common misconception, as it refers more to the duration of the surge rather than the precise timing of ovulation post-peak. *48-72 hours* - Ovulation rarely occurs this late after the peak of the **LH surge**; if it does, it suggests a potential delay or irregularity in the **ovulatory process**. - The window for successful fertilization is relatively narrow and aligns with the more immediate post-surge timing. *72-96 hours* - This time frame is significantly beyond the typical window for **ovulation** following the **LH surge**. - By this point, the egg would have either been released or the ovulatory event would have passed without the egg releasing.

Q: Which of the following does not have sympathetic noradrenergic fibers?

Sweat gland. ***Sweat gland*** - While sweat glands are innervated by the **sympathetic nervous system**, their postganglionic fibers are **cholinergic**, releasing **acetylcholine** rather than noradrenaline. - This is an important exception where sympathetic stimulation leads to acetylcholine release, causing sweating. *Blood vessels* - Most blood vessels, particularly resistance vessels such as **arterioles**, receive substantial **sympathetic noradrenergic innervation** that causes vasoconstriction. - This sympathetic tone is crucial for regulating **blood pressure** and distributing blood flow. *Heart* - The heart is richly innervated by **sympathetic noradrenergic fibers** that increase **heart rate**, **contractility**, and **conduction velocity** via beta-1 adrenergic receptors. - This makes noradrenaline a key neurotransmitter in the sympathetic regulation of cardiac function. *Eye* - The eye receives sympathetic noradrenergic innervation primarily to the **dilator pupillae muscle**, causing **mydriasis** (pupil dilation) upon activation. - These fibers also contribute to the sympathetic control of the **tarsal muscle** (Müller's muscle) in the eyelid.

Question 1

Which enzyme catalyzes oxidative deamination?

Accepted Answer

Glutamate dehydrogenase

Answer

Glutaminase

Answer

Glutamine synthase

Answer

None of the options

Question 2

Hereditary orotic aciduria Type-I is due to deficiency of?

Accepted Answer

UMP synthase

Answer

Orotate phosphoribosyl transferase

Answer

Orotic acid decarboxylase

Answer

All of the options

Question 3

Which of the following molecular interactions are found in the structure of DNA?

Accepted Answer

All of the options

Answer

Hydrogen bond

Answer

Glycosidic bond

Answer

Covalent interactions

Question 4

What is the major fibril protein associated with Primary Amyloidosis?

Accepted Answer

Immunoglobulin Light Chain

Answer

Amyloid Associated protein (AA)

Answer

Procalcitonin (PCT)

Answer

Transthyretin (TTR)

Question 5

Gastric carcinoma is associated with all of the following EXCEPT:

Accepted Answer

Activation of RAS

Answer

Over expression of C-met

Answer

Inactivation of p53

Answer

Over expression of C-erb

Question 6

In the breast, lactiferous ducts are formed under the influence of which hormone?

Accepted Answer

Estrogen

Answer

Progesterone

Answer

LH

Answer

FSH

Question 7

Which type of nerve fibers are responsible for carrying joint position and vibration sense?

Accepted Answer

A-beta fibers

Answer

A-alpha fibers

Answer

C fibers

Answer

A-delta fibers

Question 8

Sugars are primarily absorbed in?

Accepted Answer

Jejunum

Answer

Duodenum

Answer

Ascending colon

Answer

Ileum

Question 9

Ovulation occurs how long after the LH surge peak?

Accepted Answer

12-24 hours

Answer

48-72 hours

Answer

72-96 hours

Answer

24-48 hours

Question 10

Which of the following does not have sympathetic noradrenergic fibers?

Accepted Answer

Sweat gland

Answer

Heart

Answer

Eye

Answer

Blood vessels

NEET-PG 2013

Biochemistry

Pathology

Physiology