NEET-PG 2012 - Biochemistry Practice Questions

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: 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 organelle is primarily affected in Fabry's disease?

Accepted Answer

Lysosome

Answer

Endoplasmic Reticulum

Answer

Golgi apparatus

Answer

Cell membrane

Question 2

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 3

Diagnosis of carcinoid tumour is done by urinary estimation of:

Accepted Answer

5HIAA

Answer

VMA

Answer

Metanephrines

Answer

Catecholamines

Question 4

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