NEET-PG 2012 - Biochemistry Practice Questions

Q: Which amino acid in Jowar is responsible for its pellagragenic effect?

Leucine. ***Leucine*** - A high intake of **leucine**, an essential amino acid, interferes with the metabolism of **tryptophan** and niacin, leading to **pellagra**. - Jowar (sorghum) contains high levels of leucine, which, when it forms a major part of the diet, can induce **niacin deficiency**. *Lysine* - Lysine is an essential amino acid and is generally considered to be in **limited supply** in many cereal grains, making it a desirable amino acid to increase in diets. - It does not directly contribute to the pellagragenic effect; rather, a deficiency in lysine can be a nutritional concern. *Tryptophan* - Tryptophan is a **precursor to niacin (Vitamin B3)** in the body; a deficiency in tryptophan can lead to pellagra. - The high leucine content in jowar interferes with the conversion of tryptophan to niacin, thus exacerbating niacin deficiency. *Methionine* - Methionine is an **essential sulfur-containing amino acid** important for various metabolic functions and protein synthesis. - It is not directly implicated in the pellagragenic effect associated with high jowar consumption.

Q: Mechanism of cyanide poisoning is by inhibiting: NEET 2013

Cytochrome oxidase. ***Cytochrome oxidase*** - **Cyanide** is a potent poison because it binds to the **ferric iron (Fe3+)** in the active site of **cytochrome c oxidase**. - This binding completely inhibits the enzyme, halting **cellular respiration** and **ATP production**, leading to rapid cell death. *DNA synthesis* - **Cyanide** does not directly inhibit **DNA polymerase** or other enzymes involved in DNA replication. - While overall cellular processes are disrupted, its primary toxic effect is not on DNA synthesis. *Protein breakdown* - **Cyanide** does not directly interfere with proteasomes or lysosomal enzymes responsible for **protein degradation**. - Its mechanism of action is upstream, affecting energy production necessary for all cellular processes, including protein turnover. *Protein synthesis* - **Cyanide** does not directly inhibit **ribosomes** or the enzymatic machinery for **protein synthesis**. - The lack of **ATP** caused by cyanide poisoning would eventually shut down protein synthesis, but this is a secondary effect, not the primary mechanism of action.

Q: Which organelle is primarily affected in Fabry's disease?

Lysosome. ***Lysosome*** - Fabry's disease is a **lysosomal storage disorder** caused by a deficiency of the enzyme **alpha-galactosidase A**. - This enzyme deficiency leads to the accumulation of **globotriaosylceramide (Gb3)** within lysosomes in various cells throughout the body. *Endoplasmic Reticulum* - The **endoplasmic reticulum** is involved in protein synthesis and folding, and lipid metabolism. - While cellular stress from Gb3 accumulation can indirectly affect the ER, it is not the primary organelle involved in the storage of the accumulated substrate in Fabry's disease. *Golgi apparatus* - The **Golgi apparatus** modifies, sorts, and packages proteins and lipids. - It is not the site of primary pathology or substrate accumulation in lysosomal storage diseases. *Cell membrane* - The **cell membrane** regulates passage of substances into and out of the cell. - While lysosomal dysfunction can ultimately impact overall cell function, the cell membrane itself is not the organelle where the undigested substrate accumulates in Fabry's disease.

Q: In which of the following conditions is a Barr body absent in females?

45 X0 genome. ***45 X0 genome*** - A Barr body is a **condensed, inactivated X chromosome** found in somatic cells of females with at least two X chromosomes. - Individuals with a **45 X0 genome** (Turner Syndrome) have only one X chromosome, therefore no Barr body is formed. *46 XX genome* - Individuals with a **46 XX genome** are typical females and will have one Barr body per somatic cell, as one of the two X chromosomes is inactivated. - This is the normal female karyotype. *47 XXX* - Individuals with a **47 XXX genome** (triple X syndrome) have two Barr bodies per somatic cell, as two of their three X chromosomes are inactivated. - The number of Barr bodies is typically one less than the number of X chromosomes. *None of the options* - This option is incorrect because the 45 X0 genome indeed leads to the absence of a Barr body in females. - There is a specific condition listed among the options where a Barr body is absent.

Q: Diagnosis of carcinoid tumour is done by urinary estimation of:

5HIAA. ***5HIAA*** - The urinary estimate of **5-hydroxyindoleacetic acid (5HIAA)** is the primary diagnostic test for **carcinoid tumors** [1], particularly those secreting serotonin. - Elevated levels of **5HIAA** in urine indicate excessive serotonin production, which is characteristic of these tumors. *VMA* - **Vanillylmandelic acid (VMA)** is a metabolite of catecholamines and is primarily used in diagnosing **neuroblastoma** or **pheochromocytoma**, not carcinoid tumors. - Although it indicates catecholamine secretion, it does not correlate with **serotonin** levels associated with carcinoid tumors. *Metanephrines* - **Metanephrines** represent metabolites of catecholamines and are mainly evaluated for **pheochromocytoma**. - They do not provide information on serotonin metabolism or carcinoid tumor activity. *Catecholamines* - Catecholamines such as **epinephrine and norepinephrine** are not specifically related to carcinoid tumors and often indicate other neuroendocrine tumors. - Their levels do not correlate with serotonin or its metabolite, **5HIAA**, used for carcinoid diagnosis. **References:** [1] Cross SS. Underwood's Pathology: A Clinical Approach. 6th ed. (Basic Pathology) introduces the student to key general principles of pathology, both as a medical science and as a clinical activity with a vital role in patient care. Part 2 (Disease Mechanisms) provides fundamental knowledge about the cellular and molecular processes involved in diseases, providing the rationale for their treatment. Part 3 (Systematic Pathology) deals in detail with specific diseases, with emphasis on the clinically important aspects., pp. 12-15.

Q: In a patient with suspected vitamin B12 deficiency, which condition would result in an abnormal Schilling test?

Intrinsic factor deficiency. ***Intrinsic factor deficiency*** - The Schilling test assesses the absorption of **vitamin B12**. **Intrinsic factor** is crucial for B12 absorption in the ileum. - Deficiency of intrinsic factor, as seen in **pernicious anemia**, directly impairs B12 absorption, leading to an abnormal Schilling test result [1]. *Amylase deficiency* - **Amylase** is an enzyme involved in the digestion of carbohydrates, not vitamin B12 absorption [2]. - Its deficiency would primarily cause carbohydrate malabsorption symptoms, not an abnormal Schilling test. *Pancreatic endocrine insufficiency* - **Pancreatic endocrine function** relates to hormone production (e.g., insulin, glucagon), while exocrine function involves digestive enzymes. - Impairment of endocrine function does not directly affect vitamin B12 absorption or the Schilling test. *Lipase deficiency* - **Lipase** is an enzyme essential for the digestion of fats [2]. - Its deficiency would lead to fat malabsorption (steatorrhea) but would not affect vitamin B12 absorption or the Schilling test results.

Q: Selenium deficiency is seen in -

Keshan disease. ***Keshan disease*** - **Keshan disease** is a form of **cardiomyopathy** caused by **selenium deficiency**, particularly prevalent in regions with selenium-poor soil. - It presents with **heart failure**, arrhythmias, and cardiac enlargement. *Wilson disease* - **Wilson disease** is a disorder of **copper metabolism**, leading to excessive copper accumulation in organs, primarily the liver and brain. - It is not related to selenium deficiency. *Acrodermatitis enteropathica* - **Acrodermatitis enteropathica** is a genetic disorder of **zinc deficiency**, characterized by dermatitis, diarrhea, and alopecia. - It does not involve selenium deficiency. *None of the options* - This option is incorrect because Keshan disease is directly linked to selenium deficiency.

Q: Which vitamin deficiency is most commonly associated with chronic alcohol consumption and may require supplementation in alcohol use disorders?

Thiamine. ***Thiamine*** - **Thiamine** (Vitamin B1) deficiency is extremely common in chronic alcoholics due to **poor dietary intake**, impaired absorption, and increased excretion. - Deficiency can lead to serious neurological complications like **Wernicke-Korsakoff syndrome**, characterized by confusion, ataxia, and ophthalmoplegia. *Pyridoxine* - **Pyridoxine** (Vitamin B6) deficiency can occur in alcoholics, but it is less common and less clinically significant than thiamine deficiency. - While it can manifest as peripheral neuropathy or **sideroblastic anemia**, it is not the most common or critical deficiency in this population. *Riboflavin* - **Riboflavin** (Vitamin B2) deficiency can also be seen in chronic alcoholics due to poor nutrition. - Symptoms like **cheilosis** and **angular stomatitis** are mild compared to the severe neurological consequences of thiamine deficiency. *Niacin* - **Niacin** (Vitamin B3) deficiency, known as **pellagra**, is rare in developed countries but can occur in severe malnutrition, including in some alcoholics. - Pellagra presents with the "3 Ds": **dermatitis**, **diarrhea**, and **dementia**, but it is generally less prevalent than thiamine deficiency in alcohol use disorders.

Q: Which of the following is a 17β-OH steroid?

Androgen. ***Androgen*** - **Testosterone** is the classic example of a **17β-hydroxysteroid**, containing a hydroxyl group (-OH) at the **17β-position** of its steroid nucleus. - Other androgens like **androstenediol** and **dehydroepiandrosterone (DHEA)** derivatives also possess the **17β-OH configuration**. - This structural feature is essential for **androgen receptor binding** and biological activity in target tissues. - The 17β-hydroxyl group distinguishes active androgens from their inactive 17-ketosteroid metabolites. *Estrogen* - **Estradiol**, the primary estrogen, also contains a **17β-hydroxyl group**, making it technically a 17β-OH steroid. - However, in the context of steroid chemistry and clinical biochemistry, **testosterone** (androgen) is more commonly referenced as the prototypical **17β-hydroxysteroid**. - Both androgens and estrogens can be 17β-OH steroids, but androgens are the primary class associated with this terminology in medical literature. *Progesterone* - **Progesterone** is a C21 steroid with a **ketone group at C3 and C20**, not a hydroxyl group. - At position 17, progesterone has an **acetyl side chain** (CH3CO-), not a hydroxyl group. - It lacks the 17β-OH configuration that characterizes androgenic and estrogenic steroids. *None of the options* - This is incorrect because **androgen** (specifically testosterone) is a well-established **17β-hydroxysteroid**. - The measurement of **17-ketosteroids** (oxidized metabolites of 17β-OH steroids) in urine was historically used to assess androgen production.

Question 1

Which amino acid in Jowar is responsible for its pellagragenic effect?

Accepted Answer

Leucine

Answer

Lysine

Answer

Tryptophan

Answer

Methionine

Question 2

Mechanism of cyanide poisoning is by inhibiting: NEET 2013

Accepted Answer

Cytochrome oxidase

Answer

DNA synthesis

Answer

Protein breakdown

Answer

Protein synthesis

Question 3

Which organelle is primarily affected in Fabry's disease?

Accepted Answer

Lysosome

Answer

Endoplasmic Reticulum

Answer

Golgi apparatus

Answer

Cell membrane

Question 4

In which of the following conditions is a Barr body absent in females?

Accepted Answer

45 X0 genome

Answer

46 XX genome

Answer

47 XXX

Answer

None of the options

Question 5

Diagnosis of carcinoid tumour is done by urinary estimation of:

Accepted Answer

5HIAA

Answer

VMA

Answer

Metanephrines

Answer

Catecholamines

Question 6

In a patient with suspected vitamin B12 deficiency, which condition would result in an abnormal Schilling test?

Accepted Answer

Intrinsic factor deficiency

Answer

Amylase deficiency

Answer

Pancreatic endocrine insufficiency

Answer

Lipase deficiency

Question 7

Selenium deficiency is seen in -

Accepted Answer

Keshan disease

Answer

Wilson disease

Answer

Acrodermatitis enteropathica

Answer

None of the options

Question 8

Which vitamin deficiency is most commonly associated with chronic alcohol consumption and may require supplementation in alcohol use disorders?

Accepted Answer

Thiamine

Answer

Pyridoxine

Answer

Riboflavin

Answer

Niacin

Question 9

Which of the following is a 17β-OH steroid?

Accepted Answer

Androgen

Answer

Estrogen

Answer

Progesterone

Answer

None of the options

NEET-PG 2012 — Biochemistry