NEET-PG 2013 - Biochemistry Practice Questions

Q: What is the effect of moderate alcohol consumption on lipid profiles in dyslipidemia?

Increased HDL levels. ***Increased HDL levels*** - Moderate alcohol consumption is known to **increase high-density lipoprotein (HDL) cholesterol levels**, which is often considered beneficial for cardiovascular health. - This effect is thought to be mediated by alcohol's influence on **hepatic lipoprotein metabolism**, leading to enhanced HDL production and reduced catabolism. *Decreased HDL levels* - This is incorrect, as multiple studies have consistently shown that **moderate alcohol consumption** tends to elevate, rather than decrease, HDL cholesterol. - Low HDL levels are associated with increased cardiovascular risk, making this effect an undesirable outcome that is not typical of moderate drinking. *Increased triglyceride levels* - While heavy or chronic alcohol consumption can lead to **increased triglyceride levels**, moderate intake typically has a neutral or only slightly elevated effect, if any, often overshadowed by the HDL increase. - Significant hypertriglyceridemia is a concern with **excessive alcohol use**, not usually with moderate consumption in healthy individuals. *Decreased LDL levels* - Moderate alcohol consumption generally has **little to no significant effect** on **low-density lipoprotein (LDL) cholesterol levels**, often referred to as "bad" cholesterol. - While HDL increases are observed, alcohol does not effectively lower LDL, which is a primary target in the management of dyslipidemia.

Q: Which of the following statements about Maple Syrup Urine Disease (MSUD) is true?

Deficiency of branched chain amino acid enzymes. ***Deficiency of branched chain amino acid enzymes*** - MSUD is caused by a deficiency in the **branched-chain alpha-keto acid dehydrogenase complex (BCKDC)**, an enzyme responsible for metabolizing **leucine, isoleucine, and valine**. - This enzyme deficiency leads to the accumulation of these **branched-chain amino acids (BCAAs)** and their corresponding branched-chain alpha-keto acids in the body. *Asymptomatic* - MSUD is a severe metabolic disorder that is **not asymptomatic**; it typically presents with distinct neurological and metabolic symptoms shortly after birth. - Clinical manifestations can include **poor feeding, lethargy, seizures**, and a characteristic **maple syrup odor** in urine and earwax. *FeCl3 turns navy blue* - The **ferric chloride test (FeCl3 test)** in MSUD typically yields a **green-gray or dark-green color** when testing for the accumulation of alpha-keto acids (specifically alpha-ketoisocaproic acid). - A **navy blue color** with FeCl3 is more characteristic of **alkaptonuria** due to the presence of homogentisic acid. *Hyperaminoaciduria of aromatic amino acids* - MSUD is characterized by the accumulation and excretion of **branched-chain amino acids (leucine, isoleucine, valine)** and their corresponding keto acids. - **Hyperaminoaciduria of aromatic amino acids** (e.g., phenylalanine, tyrosine, tryptophan) is seen in other conditions like **phenylketonuria (PKU)**, not MSUD.

Q: Which of the following conditions is primarily treated with Vitamin B6?

Homocystinuria. ***Homocystinuria*** - The most common form of **homocystinuria** is caused by **cystathionine β-synthase (CBS) deficiency**, which requires **pyridoxal phosphate (Vitamin B6)** as a cofactor. - Approximately **50% of patients** with CBS deficiency are **B6-responsive**, making **high-dose Vitamin B6 (100-500 mg/day)** a **first-line primary treatment** for these cases. - This is a **clinically significant condition** that requires treatment, manifesting with features like **ectopia lentis, marfanoid habitus, intellectual disability, and thromboembolism**. - B6 supplementation enhances residual CBS enzyme activity and reduces plasma homocysteine levels. *Cystathionuria* - Caused by **cystathionine γ-lyase deficiency**, which also uses **Vitamin B6** as a cofactor. - This is generally a **benign, asymptomatic condition** that does **NOT require treatment**. - While B6 can reduce cystathionine accumulation, it is **not a primary treatment indication** because the condition is clinically insignificant. *Xanthurenic aciduria* - Caused by **kynureninase deficiency** in the **tryptophan metabolism pathway**, which requires **pyridoxal phosphate**. - This is a **rare and usually benign condition** that does not typically require treatment. - Not a primary indication for B6 therapy. *None of the options* - Incorrect, as **Homocystinuria** (CBS deficiency) is a **primary indication** for high-dose Vitamin B6 therapy in B6-responsive patients.

Q: 3 beta hydroxysteroid dehydrogenase deficiency causes increased production of -

DHEA. ***DHEA*** - The enzyme **3 beta-hydroxysteroid dehydrogenase (3β-HSD)** is crucial for converting **delta-5 steroids (pregnenolone, 17-OH-pregnenolone, and DHEA)** into **delta-4 steroids (progesterone, 17-OH-progesterone, and androstenedione)**. - A **deficiency** in 3β-HSD leads to the accumulation of its substrates, particularly **DHEA (dehydroepiandrosterone)** and **17-OH-pregnenolone**, due to the impaired conversion in the steroid synthesis pathway. - Among the accumulated substrates, **DHEA** has weak androgenic activity, making it clinically significant in this enzyme deficiency. *Progesterone* - **Progesterone** is a delta-4 steroid, which is synthesized from **pregnenolone** via the action of **3β-HSD**. - A deficiency in this enzyme would **decrease** the production of progesterone, not increase it, as the enzyme is required for its synthesis. *Deoxycortisol* - **Deoxycortisol (11-deoxycortisol)** is a precursor to cortisol, formed later in the adrenal steroid synthesis pathway from **17-hydroxyprogesterone**. - Its production would be **decreased** by a 3β-HSD deficiency, as the pathway is blocked upstream, reducing the formation of downstream products like cortisol and its precursors. *Estradiol* - **Estradiol** is an estrogen, synthesized from androgens (like testosterone) via the enzyme **aromatase**. - A deficiency in 3β-HSD would impair the production of androgens like androstenedione and testosterone, which are precursors for estradiol, thereby leading to a **decrease** in estradiol levels, not an increase.

Q: Which of the following is not classified as a cutaneous porphyria?

Sideroblastic anemia. ***Hereditary coproporphyria*** - This condition is primarily associated with **acute episodes** and **neuropathy**, rather than cutaneous manifestations. [2] - Unlike cutaneous porphyrias, symptoms are more systemic and do not commonly present with **skin lesions**. Although skin features can occur in some instances, they mimic porphyria cutanea tarda. [2] *Congenital erythropoeitic porphyria* - Characterized by severe **cutaneous symptoms** such as blistering and photosensitivity due to **skin exposure**. - Patients exhibit notable **facial disfigurement** and can have **hemolytic anemia**, aligning it clearly with the cutaneous forms of porphyria. *Sideroblastic anemia* - This condition involves issues with **hemoglobin synthesis** and does not fit the porphyria classification. [1] - It primarily presents with **microcytic anemia**, and the symptoms are primarily hematological, not cutaneous. [1] *Erythropoeitic porphyria* - Characterized by **severe photosensitivity** and skin manifestations, similar to congenital erythropoeitic porphyria. [1] - Patients may develop **blisters** and **hyperpigmentation** upon sun exposure, categorizing it among cutaneous porphyrias. [2]

Q: Mechanism of cyanide poisoning is by inhibiting:

Cytochrome oxidase. ***Cytochrome oxidase*** - Cyanide poisoning works by **irreversibly binding** to the ferric ion (Fe3+) in **cytochrome c oxidase** (Complex IV) of the electron transport chain. - This binding prevents the enzyme from carrying electrons to oxygen, thereby **halting cellular respiration** and ATP production. *Mitochondrial DNA synthesis* - While mitochondria are affected, cyanide does not primarily disrupt **DNA synthesis** in these organelles. - Its main target is the process of energy generation, not genetic replication. *ATP production* - Although cyanide poisoning ultimately leads to a **cessation of ATP production**, this is the *consequence* of its action, not the primary mechanism. - The direct mechanism involves inhibiting a key enzyme in the electron transport chain. *Electron transport chain* - Cyanide does indeed inhibit the **electron transport chain**, but this option is too broad. - The most specific mechanism targets a particular complex within the chain, which is **cytochrome oxidase**.

Q: Which of the following is caused by congenital 17 hydroxylase deficiency:

Hypertension. ***Hypertension*** - **Congenital 17-hydroxylase deficiency** leads to impaired synthesis of **cortisol** and **sex steroids**, resulting in an accumulation of **mineralocorticoid precursors (corticosterone and deoxycorticosterone)** [1]. - Increased levels of these mineralocorticoids cause **sodium and water retention**, leading to **hypertension** and **hypokalemia**. *Virilism* - **17-hydroxylase deficiency** impairs **androgen synthesis**, preventing the development of male secondary sexual characteristics [2]. - Individuals with this deficiency often present with **female external genitalia** regardless of their genetic sex, or **under-virilization** in genetic males, not virilism [2]. *Hyperkalemia* - The excess mineralocorticoids (deoxycorticosterone) in **17-hydroxylase deficiency** promote **sodium reabsorption** and **potassium excretion** in the kidneys [1]. - This leads to **hypokalemia**, which is the opposite of hyperkalemia. *Hermaphroditism* - **17-hydroxylase deficiency** affects the development of gonads and internal reproductive organs depending on genetic sex. - Genetic males (**XY**) with this deficiency typically develop **female external genitalia** (pseudohermaphroditism or 46, XY DSD), while genetic females (**XX**) typically present as normal females but with **primary amenorrhea** [2]. This genetic condition does not result in true hermaphroditism (presence of both ovarian and testicular tissue) [2].

Question 1

What is the effect of moderate alcohol consumption on lipid profiles in dyslipidemia?

Accepted Answer

Increased HDL levels

Answer

Decreased HDL levels

Answer

Increased triglyceride levels

Answer

Decreased LDL levels

Question 2

Which of the following statements about Maple Syrup Urine Disease (MSUD) is true?

Accepted Answer

Deficiency of branched chain amino acid enzymes

Answer

FeCl3 turns navy blue

Answer

Asymptomatic

Answer

Hyperaminoaciduria of aromatic amino acids

Question 3

Which of the following conditions is primarily treated with Vitamin B6?

Accepted Answer

Homocystinuria

Answer

Cystathionuria

Answer

None of the options

Answer

Xanthourenic aciduria

Question 4

3 beta hydroxysteroid dehydrogenase deficiency causes increased production of -

Accepted Answer

DHEA

Answer

Progesterone

Answer

Deoxycortisol

Answer

Estradiol

Question 5

Which one of the following has the maximum ionization potential?

Accepted Answer

Helium ion

Answer

Hydrogen ion

Answer

Neutron

Answer

Helium atom

Question 6

Which of the following is not classified as a cutaneous porphyria?

Accepted Answer

Sideroblastic anemia

Answer

Congenital erythropoietic porphyria

Answer

Erythropoietic protoporphyria

Answer

Hereditary coproporphyria

Question 7

True statement about vitamin K is?

Accepted Answer

Vitamin K affects bone health by activating proteins that bind calcium

Answer

Vitamin K is needed for action of clotting factor 8

Answer

Vitamin K deficiency leads to DVT

Answer

Vitamin K is water soluble

Question 8

Mechanism of cyanide poisoning is by inhibiting:

Accepted Answer

Cytochrome oxidase

Answer

Mitochondrial DNA synthesis

Answer

ATP production

Answer

Electron transport chain

Question 9

Which of the following is caused by congenital 17 hydroxylase deficiency:

Accepted Answer

Hypertension

Answer

Virilism

Answer

Hyperkalemia

Answer

Hermaphroditism

NEET-PG 2013 — Biochemistry