NEET-PG 2024 Practice Questions

Q: A patient presents with a skin rash that is exaggerated on sun exposure. What is the repair mechanism involved in this condition?

Nucleotide excision repair. ***Nucleotide excision repair*** - This mechanism is responsible for repairing **bulky lesions** in DNA, such as **pyrimidine dimers** caused by **UV radiation** from sun exposure. - Patients with defects in nucleotide excision repair (e.g., **xeroderma pigmentosum**) are highly sensitive to sunlight and develop skin rashes, pigment changes, and skin cancers. *Base excision repair* - This pathway primarily corrects **small damaged bases** that do not cause significant distortion of the DNA helix, such as deaminated, oxidized, or alkylated bases. - It does not primarily address the bulky lesions induced by UV light that cause exaggerated sun sensitivity. *Mismatch repair* - This system corrects errors, like **mismatched base pairs**, that are incorporated during DNA replication. - It is not directly involved in repairing DNA damage caused by environmental factors like UV radiation. *Double stranded DNA break repair* - This mechanism repairs **double-strand breaks** in DNA, which are highly deleterious lesions caused by ionizing radiation or oxidative stress. - While critical for genome stability, it is not the primary repair pathway for UV-induced DNA lesions or the direct cause of sun sensitivity.

Q: A 45-year-old patient presents with joint pain and weakness and is known to have homocystinuria. Which vitamin is required in the treatment?

Vitamin B6. ***Vitamin B6*** - **Homocystinuria** is often caused by a deficiency in the enzyme **cystathionine beta-synthase**, which requires **pyridoxal phosphate (active form of B6)** as a cofactor. - Supplementation with high-dose **vitamin B6** can help some patients by increasing the residual activity of the enzyme, thereby reducing **homocysteine levels**. - This is the **primary treatment** for **B6-responsive homocystinuria** (approximately 50% of cases respond to B6 therapy). *Vitamin B12* - Vitamin B12 is a cofactor for the enzyme **methionine synthase**, which converts homocysteine back to methionine. - While it plays a role in homocysteine metabolism, **vitamin B6** is typically the primary treatment for homocystinuria caused by **cystathionine beta-synthase deficiency**. *Vitamin B9* - Vitamin B9 (folic acid) works together with **vitamin B12** as a cofactor in the **remethylation pathway** via methionine synthase. - While folate supplementation may help lower homocysteine levels, it is **not the primary treatment** for classical homocystinuria due to cystathionine beta-synthase deficiency. - **Vitamin B6** remains the first-line vitamin therapy for enzyme deficiency-related homocystinuria. *Vitamin B7* - Vitamin B7, or **biotin**, is a cofactor for carboxylase enzymes and is involved in fatty acid synthesis and gluconeogenesis. - It has no direct role in the metabolism of **homocysteine** or the treatment of homocystinuria. *Vitamin B1* - Vitamin B1, or **thiamine**, is essential for carbohydrate metabolism and nerve function. - It is not involved in the metabolic pathways that regulate **homocysteine levels** or the treatment of homocystinuria.

Q: Identify the type of inhibition exhibited by A?

Competitive inhibition. ***Competitive inhibition*** - In competitive inhibition, the Lineweaver-Burk plot shows that the lines for inhibited and uninhibited reactions **intersect at the Y-axis**, indicating **Vmax is unchanged**. - The X-intercept moves closer to zero (or to the right if the intercept is negative), signifying an **increase in apparent Km**. *Uncompetitive inhibition* - This type of inhibition is characterized by **parallel lines** on a Lineweaver-Burk plot, as both **Vmax and Km are decreased proportionally**. - The lines do not intersect with each other or with the uninhibited line at either axis. *Mixed inhibition* - In mixed inhibition, the inhibitor can bind to both the free enzyme and the enzyme-substrate complex. - The lines on the Lineweaver-Burk plot **intersect to the left of the Y-axis but not on the X-axis**, indicating changes in both Km and Vmax. *Non-competitive inhibition* - This is a specific type of mixed inhibition where the inhibitor binds equally well to the free enzyme and the enzyme-substrate complex. - The Lineweaver-Burk plot shows lines that **intersect at the X-axis**, indicating **Km is unchanged** while **Vmax is decreased**. *Allosteric inhibition* - Allosteric inhibition involves binding of an inhibitor to a site other than the active site, causing conformational changes. - This type of inhibition **cannot be reliably distinguished using Lineweaver-Burk plots alone**, as it may show patterns similar to mixed or non-competitive inhibition depending on the mechanism.

Q: A patient who has always neglected his nutrition presented with follicular hyperkeratosis on the extensor aspect of the forearm. What is the diagnosis?

Phrynoderma. ***Phrynoderma*** - **Phrynoderma**, also known as **toad skin**, is characterized by **follicular hyperkeratosis**, particularly on the **extensor surfaces** of limbs like the forearm. - This condition is closely linked to **nutritional deficiencies**, often involving **vitamin A**, **essential fatty acids**, or sometimes **B vitamins**. *Eruptive xanthoma* - **Eruptive xanthomas** are small, yellow-red papules that often appear suddenly, typically on the **buttocks**, **extensor surfaces of the limbs**, and **trunk**. - They are a cutaneous manifestation of **severe hypertriglyceridemia** and not primarily related to general nutritional neglect or follicular hyperkeratosis. *Darier's disease* - **Darier's disease** is a **rare, inherited genetic disorder** characterized by greasy, crusted papules primarily in **seborrheic areas** such as the scalp, forehead, chest, and groin. - It results from a mutation in the **ATP2A2 gene**, affecting calcium signaling in keratinocytes, and is not a nutritional deficiency condition. *Folliculitis* - **Folliculitis** is the inflammation of one or more **hair follicles**, often caused by **bacterial** (e.g., *Staphylococcus aureus*) or **fungal infections**. - It presents as small, red, sometimes pus-filled bumps around hair follicles, distinct from the dry, rough texture of follicular hyperkeratosis seen in phrynoderma.

Q: A child presented with perianal itching. The swab specimen is shown in the image. What is the diagnosis?

Enterobius. ***Enterobius*** - The image shows **D-shaped** (plano-convex) and **transparent eggs**, which are characteristic of *Enterobius vermicularis* (**pinworm** or **threadworm**). - **Perianal itching**, especially at night, is the hallmark symptom due to the female worm migrating to the perianal region to lay eggs. *Ascaris* - *Ascaris lumbricoides* eggs are typically **round to oval**, with a thick, mamillated (bumpy) outer shell, or smooth in the case of decorticated eggs, which is different from the eggs pictured. - Infection with *Ascaris* can cause pulmonary symptoms (Loeffler's syndrome) and intestinal obstruction, but not typically perianal itching. *Trichiura* - *Trichuris trichiura* (**whipworm**) eggs are distinctly **barrel-shaped** with prominent **polar plugs** at each end, which is not seen in the image. - Whipworm infection is often associated with bloody diarrhea, rectal prolapse, and growth retardation, not primarily perianal itching. *Ancylostoma* - *Ancylostoma duodenale* and *Necator americanus* (hookworms) eggs are typically **oval** with a **thin shell** and segmented embryo (morula stage) within, which lacks the distinct D-shape and transparency of the pictured eggs. - Hookworm infection primarily causes iron-deficiency anemia and can lead to cutaneous larva migrans, not perianal itching as a primary symptom.

Q: A frequent traveler presented with 4 days of continuous fever, abdominal pain, and bradycardia. What is the best diagnostic test to confirm the pathogen?

Blood culture. ***Blood culture*** - **Blood culture** is the most sensitive and specific test for confirming **typhoid fever** in the first week of illness. - The presence of **continuous fever** (step-ladder pattern), **abdominal pain**, and **relative bradycardia** in a traveler strongly suggests typhoid fever caused by *Salmonella Typhi*. *Widal test* - The **Widal test** detects antibodies against *Salmonella Typhi* antigens and is often positive later in the disease course. - It has **limited sensitivity and specificity**, especially in endemic areas or with prior vaccination, leading to false positives and negatives. *Urine culture* - **Urine culture** has a low yield for *Salmonella Typhi*, as bacteria are intermittently shed in urine, usually later in the disease. - It's primarily useful for diagnosing **urinary tract infections** or in chronic carriers of typhoid. *Stool culture* - **Stool culture** yield is higher in the later stages of typhoid fever, as *Salmonella Typhi* is shed in feces. - Its sensitivity is lower than blood culture in the early acute phase when bacteremia is most prominent.

Q: The diagrammatic representation of the karyotype of an individual indicates a specific genetic abnormality. What is the diagnosis?

Prader-Willi syndrome. ***Prader-Willi syndrome*** - The karyotype shows an abnormality on **chromosome 15**, which is consistent with Prader-Willi syndrome caused by **deletion of 15q11-q13** inherited from the **paternal** chromosome or **maternal uniparental disomy**. - While PWS deletions are typically **submicroscopic**, larger deletions can occasionally be visible on standard karyotyping, particularly when they represent **class I deletions** that are more extensive and involve additional chromosomal material beyond the typical PWS critical region. *Angelman syndrome* - Although Angelman syndrome also involves **chromosome 15q11-q13 deletion**, it results from **maternal** deletion or **paternal uniparental disomy**, and presents with distinctly different clinical features. - Clinical presentation includes **severe intellectual disability**, **ataxia**, **seizures**, **absent speech**, and **inappropriate laughter** (happy demeanor), which differs significantly from the PWS phenotype. *DiGeorge syndrome* - DiGeorge syndrome is caused by **deletion of chromosome 22q11.2**, not chromosome 15 as shown in the karyotype. - Clinical features include **cardiac defects** (conotruncal abnormalities), **thymic hypoplasia**, **parathyroid hypoplasia** (hypocalcemia), **cleft palate**, and characteristic facial features (CATCH-22 syndrome). *Cri du Chat syndrome* - This syndrome results from **deletion of chromosome 5p** (short arm of chromosome 5), not chromosome 15 as indicated in the karyotype. - Characteristic features include **high-pitched cry** resembling a cat's meow in infancy, **intellectual disability**, **microcephaly**, and **distinctive facial features**.

Q: A patient with a history of binge alcohol intake presented to the emergency department with convulsions, altered sensorium, and a plasma glucose level of $45 \mathrm{mg} / \mathrm{dL}$. Which of the following treatments is needed?

Thiamine followed by Dextrose. ***Thiamine followed by Dextrose*** - In patients with **alcoholism** and suspected **hypoglycemia**, thiamine should always be administered before or concurrently with dextrose to prevent **Wernicke encephalopathy**. - Dextrose alone can precipitate or worsen Wernicke encephalopathy in **thiamine-deficient** individuals by increasing carbohydrate metabolism, thereby depleting residual thiamine. *Thiamine* - While **thiamine** is crucial for patients with chronic alcohol intake, administering it alone will not immediately resolve the **hypoglycemia** and associated neurological symptoms like convulsions and altered sensorium. - Thiamine is essential to prevent complications like **Wernicke-Korsakoff syndrome**, but the immediate life-threatening issue is the low blood glucose. *25% Dextrose* - Administering **dextrose** alone to an **alcohol-dependent** patient is risky because it can precipitate or worsen **Wernicke's encephalopathy** by increasing glucose metabolism without adequate thiamine. - While dextrose will correct the **hypoglycemia**, its administration without prior thiamine is contraindicated in this patient population. *Glucagon* - **Glucagon** works by mobilizing hepatic glycogen stores to raise blood glucose levels. - In patients with **chronic alcohol intake**, hepatic glycogen stores are often **depleted**, making glucagon ineffective. - Additionally, glucagon has a **slower onset** compared to intravenous dextrose, making it unsuitable for this emergency situation with convulsions and altered sensorium. *Fomepizole* - **Fomepizole** is an antidote used in cases of **methanol** or **ethylene glycol poisoning** to inhibit alcohol dehydrogenase. - It is not indicated for treating **alcohol withdrawal**, **hypoglycemia**, or related complications in patients with binge alcohol intake.

Q: Methotrexate use causes reduced synthesis of which of the following?

TMP. ***TMP (Thymidylate)*** - Methotrexate is a **folate analog** that inhibits **dihydrofolate reductase (DHFR)**, preventing the regeneration of tetrahydrofolate (THF) from dihydrofolate. - **Tetrahydrofolate** is essential for **thymidylate synthase**, which converts dUMP to **TMP (thymidylate)** - this is the **most directly and significantly affected** nucleotide synthesis pathway. - Reduced TMP synthesis leads to impaired DNA synthesis and is the **primary mechanism** of methotrexate's cytotoxic effects. *CMP (Cytidine monophosphate)* - CMP synthesis occurs via the **de novo pyrimidine pathway** starting from carbamoyl phosphate and aspartate, forming UMP, which is then converted to CMP. - This pathway **does not require tetrahydrofolate** cofactors, so methotrexate does not significantly affect CMP synthesis directly. *GMP (Guanosine monophosphate)* - GMP is a purine nucleotide whose synthesis **does require tetrahydrofolate** derivatives (N10-formyl-THF) at two steps in the de novo purine pathway. - However, the effect on GMP is **less direct and less pronounced** than on TMP synthesis, and cells can partially compensate through salvage pathways. *AMP (Adenosine monophosphate)* - AMP is also a purine nucleotide that requires **N10-formyl-THF** cofactors during de novo synthesis (same pathway branch point as GMP). - Like GMP, it is affected but **less directly than TMP**, and salvage pathways provide alternative synthesis routes. *UMP (Uridine monophosphate)* - UMP is synthesized through the **de novo pyrimidine pathway** which does not require folate cofactors. - Methotrexate does not inhibit the enzymes (carbamoyl phosphate synthetase II, aspartate transcarbamoylase, dihydroorotase, etc.) involved in UMP synthesis.

Question 1

A patient presents with a skin rash that is exaggerated on sun exposure. What is the repair mechanism involved in this condition?

Accepted Answer

Nucleotide excision repair

Answer

Base excision repair

Answer

Mismatch repair

Answer

Double stranded DNA break repair

Question 2

A 45-year-old patient presents with joint pain and weakness and is known to have homocystinuria. Which vitamin is required in the treatment?

Accepted Answer

Vitamin B6

Answer

Vitamin B12

Answer

Vitamin B7

Answer

Vitamin B1

Answer

Vitamin B9

Question 3

A patient came to the hospital with severe abdominal pain, and lipase levels were elevated. On imaging, a stone is found in the common bile duct (CBD). Which enzyme is most likely elevated in this condition?

Accepted Answer

ALP

Answer

ALT

Answer

GGT

Answer

LDH

Answer

AST

Question 4

Identify the type of inhibition exhibited by A?

Accepted Answer

Competitive inhibition

Answer

Uncompetitive inhibition

Answer

Mixed inhibition

Answer

Non competitive inhibition

Answer

Allosteric inhibition

Question 5

A patient who has always neglected his nutrition presented with follicular hyperkeratosis on the extensor aspect of the forearm. What is the diagnosis?

Accepted Answer

Phrynoderma

Answer

Eruptive xanthoma

Answer

Darier's disease

Answer

Folliculitis

Question 6

A child presented with perianal itching. The swab specimen is shown in the image. What is the diagnosis?

Accepted Answer

Enterobius

Answer

Ascaris

Answer

Trichiura

Answer

Ancylostoma

Question 7

A frequent traveler presented with 4 days of continuous fever, abdominal pain, and bradycardia. What is the best diagnostic test to confirm the pathogen?

Accepted Answer

Blood culture

Answer

Widal test

Answer

Urine culture

Answer

Stool culture

Question 8

The diagrammatic representation of the karyotype of an individual indicates a specific genetic abnormality. What is the diagnosis?

Accepted Answer

Prader-Willi syndrome

Answer

Angelman syndrome

Answer

Cri du Chat syndrome

Answer

DiGeorge syndrome

Question 9

A patient with a history of binge alcohol intake presented to the emergency department with convulsions, altered sensorium, and a plasma glucose level of $45 \mathrm{mg} / \mathrm{dL}$. Which of the following treatments is needed?

Accepted Answer

Thiamine followed by Dextrose

Answer

Thiamine

Answer

$25 \% $ Dextrose

Answer

Fomepizole

Answer

Glucagon

Question 10

Methotrexate use causes reduced synthesis of which of the following?

Accepted Answer

TMP

Answer

CMP

Answer

GMP

Answer

AMP

Answer

UMP

NEET-PG 2024

Biochemistry

Dermatology

Microbiology

Pathology

Pharmacology