NEET-PG 2024 - Biochemistry Practice Questions

Q: A patient's relatives sent a message on social media to the consulting doctor, mentioning that the patient's urinary coproporphyrin test is positive. What is the probable cause?

Lead poisoning. ***Lead poisoning*** - **Lead poisoning** is associated with an increase in **urinary coproporphyrin III**, as lead inhibits the enzyme **coproporphyrinogen oxidase** in the heme synthesis pathway. - This leads to the accumulation and excretion of **coproporphyrin III** in the urine, making it a valuable biomarker for lead exposure. *Asbestosis* - **Asbestosis** is a chronic lung disease caused by inhaling **asbestos fibers**, leading to diffuse interstitial fibrosis. - It does not directly affect the **heme synthesis pathway** or cause an increase in urinary coproporphyrins. *Silicosis* - **Silicosis** is a chronic occupational lung disease caused by inhaling **crystalline silica dust**, resulting in pulmonary fibrosis. - It is not associated with alterations in **porphyrin metabolism** or increased urinary coproporphyrin levels. *Mercury poisoning* - While **mercury poisoning** can affect various organ systems, including renal and neurological, it is not primarily associated with disturbances in the **heme synthesis pathway** or elevated urinary coproporphyrins. - **Mercury poisoning** often manifests with symptoms like **tremors**, **neurological deficits**, and **kidney damage**. *Arsenic poisoning* - **Arsenic poisoning** causes a variety of systemic effects including gastrointestinal symptoms, peripheral neuropathy, and skin changes (hyperpigmentation, hyperkeratosis). - Unlike lead poisoning, **arsenic does not significantly elevate urinary coproporphyrin III** levels, making it distinguishable from lead toxicity through this biomarker.

Q: A neonate was brought to the hospital with chief complaints of poor feeding, vomiting, acidosis, and cataract. Benedict's test on urine was positive, but urinary glucose was negative. What is the defective enzyme in the above-mentioned disorder?

Galactose 1-phosphate uridyl transferase. ***Galactose 1-phosphate uridyl transferase*** - This enzyme deficiency leads to **classic galactosemia**, characterized by the accumulation of **galactose-1-phosphate**, which is toxic. - Clinical features like **poor feeding, vomiting, acidosis, and cataracts** are typical, and a positive **Benedict's test** (detecting reducing sugars like galactose) with negative urinary glucose confirms the presence of another reducing sugar. *Fructokinase* - Deficiency of fructokinase causes **essential fructosuria**, a benign condition where **fructose** accumulates in the urine. - Unlike classic galactosemia, it does not present with severe symptoms like **acidosis** or **cataracts**. *Aldolase B* - **Aldolase B deficiency** causes hereditary fructose intolerance, presenting with **vomiting, hypoglycemia, and hepatomegaly** after fructose ingestion. - It does not cause **cataracts**, and Benedict's test would detect fructose, but the clinical context (symptoms with fructose/sucrose intake) differs from galactosemia. *Lactase* - **Lactase deficiency** (lactose intolerance) results in gastrointestinal symptoms such as **bloating, diarrhea, and abdominal pain** upon lactose consumption. - It does not typically cause **acidosis, cataracts**, or a positive Benedict's test in urine unless secondary bacterial fermentation leads to other reducing substances. *Sucrase* - **Sucrase-isomaltase deficiency** leads to the malabsorption of sucrose, causing symptoms similar to lactose intolerance like **diarrhea and abdominal cramping**. - It does not result in the systemic, severe metabolic derangements or signs like **cataracts** seen in classic galactosemia.

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: What is the primary function of IL-8?

Chemotaxis. ***Chemotaxis*** - **IL-8** (also known as **CXCL8**) is a potent **chemokine** that primarily functions to recruit and activate **neutrophils** to sites of inflammation. - It guides these immune cells by forming a chemical gradient, allowing them to extravasate from blood vessels and migrate to the infected or injured tissue. *Lymphocyte proliferation* - Lymphocyte proliferation is primarily stimulated by **IL-2**, which acts as a growth factor for T cells. - While IL-8 contributes to the inflammatory environment, its direct role in inducing lymphocyte cell division is minor compared to its chemotactic function. *TH1 activation* - **TH1 cell activation** is mainly driven by **IL-12** and **IFN-γ**, which promote the differentiation and function of T helper 1 cells, crucial for fighting intracellular pathogens. - IL-8's role is unrelated to guiding TH1 cell differentiation. *Fever* - Fever is primarily induced by **pyrogenic cytokines** such as **IL-1**, **IL-6**, and **TNF-α**, which act on the hypothalamus to raise body temperature. - While IL-8 is part of the inflammatory response that can sometimes coincide with fever, it does not directly act as a pyrogen. *B cell activation* - **B cell activation** and differentiation are primarily regulated by interleukins such as **IL-4**, **IL-5**, **IL-6**, and **IL-21**, which promote antibody production and class switching. - IL-8 does not play a significant role in B cell function; its action is focused on innate immunity, particularly neutrophil recruitment.

Q: An adult tall male presents with a long arm span, pectus excavatum, and cardiac abnormalities. What is the most likely defective protein?

Fibrillin. ***Fibrillin*** - The constellation of **tall stature**, **long arm span**, **pectus excavatum**, and **cardiac abnormalities** (e.g., aortic dissection or mitral valve prolapse) is classic for **Marfan syndrome**. - Marfan syndrome is caused by a defect in the *FBN1* gene, which codes for **fibrillin-1**, a glycoprotein essential for the formation of elastic fibers in connective tissue. *Elastin* - Defects in **elastin** are associated with conditions like **supravalvular aortic stenosis** (due to **Williams syndrome**) or cutis laxa, which have different phenotypic presentations. - While both elastin and fibrillin are components of elastic fibers, the specific features of Marfan syndrome point to fibrillin as the primary defect. *Collagen* - Defects in **collagen** (especially type I, III, or V) are associated with conditions such as **osteogenesis imperfecta** (brittle bones) or **Ehlers-Danlos syndrome** (hypermobility, skin hyperextensibility). - These conditions typically present with different clinical manifestations, lacking the specific combination of features seen in this patient. *Myosin* - **Myosin** is a fibrous protein primarily involved in **muscle contraction** and is not directly implicated in widespread connective tissue disorders affecting skeletal and cardiovascular systems in this manner. - Defects in myosin are more commonly associated with various forms of **cardiomyopathy** or skeletal muscle myopathies, not Marfan-like features. *Laminin* - **Laminin** is a major component of the **basement membrane** and plays a role in cell adhesion, migration, and tissue architecture. - Laminin defects are associated with certain forms of **muscular dystrophy** (e.g., congenital muscular dystrophy) and **epidermolysis bullosa**, not the specific skeletal and cardiovascular features of Marfan syndrome.

Q: A patient with homocystinuria presents with ectopia lentis (dislocation of the lens). Which vitamin should be supplemented?

Vitamin B6. ***Vitamin B6*** - Many cases of **homocystinuria** are due to a deficiency in **cystathionine beta-synthase (CBS)**, an enzyme that requires **pyridoxal phosphate (active B6)** as a cofactor. - Supplementing with **high doses of vitamin B6** can significantly improve outcomes in patients with **B6-responsive homocystinuria** by increasing residual CBS enzyme activity. *Vitamin B12* - While vitamin B12 (cobalamin) is a cofactor for **methionine synthase**, an enzyme involved in homocysteine metabolism, it is not the primary treatment for **homocystinuria due to CBS deficiency**. - B12 deficiency can lead to increased homocysteine levels, but B12 supplementation alone will not address the underlying enzyme defect in most cases of homocystinuria. *Thiamine* - **Thiamine (Vitamin B1)** is essential for carbohydrate metabolism and nerve function, but it has no direct role in the metabolic pathway involved in homocystinuria. - Thiamine deficiency causes **beriberi** and **Wernicke-Korsakoff syndrome**, symptoms distinctly different from homocystinuria. *Vitamin B9 (Folate)* - **Folate** is a cofactor for **methionine synthase**, working alongside vitamin B12 to convert homocysteine back to methionine. - While folate deficiency can contribute to hyperhomocysteinemia, it is not the primary therapeutic intervention for homocystinuria caused by **CBS deficiency**. *Vitamin C* - **Vitamin C (ascorbic acid)** is important for collagen synthesis and acts as an antioxidant, but it has no role in homocysteine metabolism or the treatment of homocystinuria. - Vitamin C deficiency causes **scurvy**, which presents with bleeding gums, petechiae, and poor wound healing—completely unrelated to homocystinuria.

Q: Which of the following foods should be consumed to prevent thiamine deficiency?

Whole grain cereals and legumes. ***Whole grain cereals and legumes*** - **Whole grain cereals** (brown rice, oats, wheat germ, fortified cereals) and **legumes** (beans, lentils, peas) are **excellent natural sources of thiamine (vitamin B1)** - They retain the **bran and germ** layers where thiamine is concentrated - Regular consumption effectively prevents **thiamine deficiency** and associated conditions like beriberi and Wernicke-Korsakoff syndrome - This is the **primary dietary recommendation** for thiamine adequacy *Polished white rice* - Polished white rice has the **bran and germ removed** during processing, eliminating most of the thiamine content - Consuming polished white rice as a staple **causes thiamine deficiency**, leading to **beriberi** (common in populations with rice-based diets) - Unless fortified with thiamine, polished white rice contributes to deficiency rather than preventing it *Dairy products and eggs* - While nutritious, dairy products and eggs contain **relatively low amounts of thiamine** - Not reliable sources for meeting daily thiamine requirements - Contribute to overall nutrition but insufficient alone to prevent thiamine deficiency *Fresh fruits and vegetables* - Most fruits and vegetables contain **modest amounts of thiamine** compared to whole grains - Some exceptions include peas, asparagus, and Brussels sprouts, but typical servings provide limited thiamine - Important for overall health but not primary thiamine sources *Red meat and poultry* - Pork is actually a **good source of thiamine**, particularly organ meats - However, **whole grains and legumes** remain the most reliable and accessible plant-based sources - Red meat and poultry provide moderate thiamine but are not the best answer for preventing deficiency in general populations

Question 1

A patient came to the emergency room with severe abdominal pain. The serum triglyceride level was $1500 \mathrm{mg} / \mathrm{dL}$. What is the most likely defect?

Accepted Answer

Apo C-II

Answer

Apo B-48

Answer

Apo B-100

Answer

LDL receptor

Answer

Lipoprotein lipase

Question 2

A patient's relatives sent a message on social media to the consulting doctor, mentioning that the patient's urinary coproporphyrin test is positive. What is the probable cause?

Accepted Answer

Lead poisoning

Answer

Asbestosis

Answer

Silicosis

Answer

Mercury poisoning

Answer

Arsenic poisoning

Question 3

A neonate was brought to the hospital with chief complaints of poor feeding, vomiting, acidosis, and cataract. Benedict's test on urine was positive, but urinary glucose was negative. What is the defective enzyme in the above-mentioned disorder?

Accepted Answer

Galactose 1-phosphate uridyl transferase

Answer

Fructokinase

Answer

Lactase

Answer

Sucrase

Answer

Aldolase B

Question 4

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 5

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 6

What is the primary function of IL-8?

Accepted Answer

Chemotaxis

Answer

Lymphocyte proliferation

Answer

TH1 activation

Answer

Fever

Answer

B cell activation

Question 7

An adult male presented with a protruding abdomen, diarrhea, visual symptoms, and neurological manifestations. His LDL is low. Based on the peripheral smear finding shown in the image, what is the likely diagnosis?

Accepted Answer

Abetalipoproteinemia

Answer

EDTA changes

Answer

Uremia

Answer

Burns

Answer

Liver disease

Question 8

An adult tall male presents with a long arm span, pectus excavatum, and cardiac abnormalities. What is the most likely defective protein?

Accepted Answer

Fibrillin

Answer

Elastin

Answer

Collagen

Answer

Myosin

Answer

Laminin

Question 9

A patient with homocystinuria presents with ectopia lentis (dislocation of the lens). Which vitamin should be supplemented?

Accepted Answer

Vitamin B6

Answer

Vitamin B12

Answer

Thiamine

Answer

Vitamin B9 (Folate)

Answer

Vitamin C

Question 10

Which of the following foods should be consumed to prevent thiamine deficiency?

Accepted Answer

Whole grain cereals and legumes

Answer

Dairy products and eggs

Answer

Fresh fruits and vegetables

Answer

Polished white rice

Answer

Red meat and poultry

NEET-PG 2024 — Biochemistry