NEET-PG 2012 Practice Questions

Q: Glucose oxidase converts glucose to?

Gluconic acid. ***Gluconic acid*** - **Glucose oxidase** specifically catalyzes the oxidation of glucose, producing **gluconic acid** and hydrogen peroxide. - This reaction forms the basis for many common **glucose diagnostic tests**, such as those used in blood glucose monitors. *Glucuronic acid* - **Glucuronic acid** is formed from the oxidation of glucose at carbon 6, typically through the **uronic acid pathway**. - It is known for its role in **detoxification** and conjugation reactions in the liver, not as a direct product of glucose oxidase. *Galactonic acid* - **Galactonic acid** is an oxidized form of galactose, a different monosaccharide from glucose. - Its formation is not associated with the action of **glucose oxidase**, an enzyme specific to glucose. *Iduronic acid* - **Iduronic acid** is a C5 epimer of glucuronic acid and is a common component of various **glycosaminoglycans** like dermatan sulfate and heparan sulfate. - It is not produced by the action of **glucose oxidase** on glucose.

Q: Which of the following is required for fatty acid synthesis ?

NADPH. ***NADPH*** - **NADPH** is crucial for fatty acid synthesis, providing the **reducing power** needed for the successive reduction steps. - The enzymes involved, such as **fatty acid synthase**, utilize **NADPH** for the conversion of keto groups to hydroxyl groups and then to saturated methylene groups. *NADH* - **NADH** plays a primary role in **oxidative phosphorylation** and the electron transport chain to generate ATP. - It is generally produced during **catabolic reactions** and is not primarily used as a reducing agent in anabolic processes like fatty acid synthesis. *FADH* - **FADH2** (reduced form of FAD, not FADH) is a coenzyme involved in redox reactions, particularly in the **Krebs cycle** and beta-oxidation of fatty acids. - Like NADH, it is mostly involved in **catabolic processes** that generate energy, rather than anabolic processes requiring reducing equivalents for synthesis. *None of the options* - This option is incorrect because **NADPH** is indeed required for fatty acid synthesis, serving as the essential reducing agent. - The other coenzymes mentioned (NADH, FADH) have different metabolic roles, primarily in energy production rather than biosynthesis.

Q: Which hormone inhibits hormone-sensitive lipase?

Insulin. ***Insulin*** - **Insulin** is a key anabolic hormone that promotes energy storage and inhibits catabolic processes, including the breakdown of triglycerides. - It directly inhibits **hormone-sensitive lipase (HSL)** activity, thus reducing the release of free fatty acids from adipose tissue. *Thyroid hormone* - **Thyroid hormones** (T3 and T4) generally promote catabolism and increase metabolic rate, including the mobilization of lipids. - They tend to **stimulate rather than inhibit** hormone-sensitive lipase expression and activity. *GH* - **Growth hormone (GH)** has lipolytic effects, meaning it promotes the breakdown of fats to provide energy. - GH typically **stimulates HSL activity** and increases the release of free fatty acids from adipocytes. *ACTH* - **Adrenocorticotropic hormone (ACTH)** primarily stimulates the adrenal cortex to produce cortisol. - **Cortisol** can have lipolytic effects in certain contexts and does not directly inhibit HSL; instead, catecholamines act as direct stimulators of HSL.

Q: Which of the following is a tripeptide?

Glutathione. ***Glutathione*** - **Glutathione** is a tripeptide composed of three amino acids: **glutamate**, **cysteine**, and **glycine**. - It plays a crucial role as an **antioxidant** in the body, protecting cells from damage by **free radicals**. *Angiotensin* - **Angiotensin** is a peptide hormone that causes **vasoconstriction** and an increase in **blood pressure**. - It is an **oligopeptide** (typically 8-10 amino acids) rather than a tripeptide. *Glucagon* - **Glucagon** is a peptide hormone produced by the **alpha cells** of the pancreas that raises **blood glucose levels**. - It is a **29-amino acid** polypeptide, much larger than a tripeptide. *Oxytocin* - **Oxytocin** is a hormone involved in social bonding and sexual reproduction, best known for its role in **childbirth** and **lactation**. - It is a **nonapeptide**, meaning it consists of nine amino acids.

Q: What is the primary mechanism by which epinephrine reduces insulin secretion?

Predominantly through alpha action. ***Predominantly through alpha action*** - **Epinephrine** primarily reduces insulin secretion by stimulating **alpha-2 adrenergic receptors** on pancreatic beta cells. - Activation of these receptors leads to a decrease in **cAMP levels** and an inhibition of insulin release. *Predominantly through beta action* - **Beta-2 adrenergic receptor activation** on pancreatic beta cells typically **stimulates** insulin secretion, which is opposite to epinephrine's overall effect. - While epinephrine has both alpha and beta effects, the **alpha-2 inhibition** of insulin release predominates in this context. *Through both alpha and beta actions* - Although epinephrine exerts both alpha and beta effects, the **alpha-2 receptor-mediated inhibition** of insulin secretion is the dominant mechanism. - The **beta-2 receptor-mediated stimulation** of insulin release is overridden by the stronger inhibitory alpha-2 effect. *Through muscarinic receptors* - Muscarinic receptors are part of the **parasympathetic nervous system** and are involved in stimulating insulin secretion. - **Epinephrine** acts on adrenergic receptors, not muscarinic receptors, to influence insulin release.

Q: Insulin is essential for glucose entry in?

Muscle cells. ***Muscle cells*** - **Insulin** promotes glucose uptake into **muscle cells** by stimulating the translocation of **GLUT4 transporters** to the cell surface. - In the absence of insulin, **glucose uptake** into quiescent muscle cells is significantly reduced. *Cortical neurons* - **Neurons** in the brain, including cortical neurons, primarily utilize **GLUT1** and **GLUT3 transporters** for glucose uptake, which are **insulin-independent**. - This ensures a constant supply of glucose to the brain, even during periods of low insulin. *Beta cells of pancreas* - **Pancreatic beta cells** use **GLUT2 transporters** for glucose uptake, which are **insulin-independent** and have a high capacity. - This allows beta cells to sense glucose levels and regulate insulin secretion accordingly. *Renal tubular cells* - **Renal tubular cells** reabsorb glucose primarily through **sodium-glucose co-transporters (SGLTs)** and **GLUT2 transporters**, both of which are **insulin-independent**. - Their primary role is in maintaining glucose homeostasis by preventing glucose loss in urine.

Q: Substance that is completely reabsorbed from the kidney?

Glucose. ***Glucose*** - In a healthy individual, **virtually all filtered glucose** is reabsorbed in the proximal convoluted tubule via **sodium-glucose cotransporters (SGLTs)**. - This complete reabsorption ensures that this vital energy source is conserved and not excreted in the urine. *Na+* - While a large proportion of filtered **Na+** is reabsorbed to maintain fluid and electrolyte balance, not all of it is reabsorbed; some is excreted in urine. - The reabsorption of Na+ is **regulated** by hormones like **aldosterone** to fine-tune its excretion based on the body's needs. *K+* - **K+** undergoes both reabsorption and secretion in different parts of the nephron, and its excretion is tightly regulated. - Net reabsorption of K+ is not complete; its handling ensures appropriate plasma levels are maintained for muscle and nerve function. *Urea* - Approximately **50% of filtered urea undergoes reabsorption** in the renal tubules, while the other half is excreted. - Urea reabsorption is important for generating the **medullary osmotic gradient**, which is essential for concentrating urine, but it is never completely reabsorbed.

Q: Which isotope is used to measure RBC volume?

Cr 51. ***Cr 51*** - **Chromium-51** attaches irreversibly to the beta chain of hemoglobin, making it an ideal tracer for measuring **red blood cell volume** and survival. - After injection, the labeled red blood cells distribute throughout the circulation, and their dilution allows for the calculation of the total **RBC mass**. *H-3* - **Tritium (H-3)** is typically used as tritiated water to measure **total body water**, as it readily equilibrates throughout all fluid compartments. - It does not specifically bind to red blood cells for mass measurement. *D2O* - **D2O (heavy water)** is used to measure **total body water** content, similar to tritiated water. - It exchanges with water in the body and diffuses into all fluid compartments, rather than targeting red blood cells. *I-135* - While various **iodine isotopes** are used in medicine, such as **I-131** for thyroid imaging or therapy, **I-135** is not a commonly used isotope for measuring red blood cell volume. - Other tracers like **radio-iodinated human serum albumin** (e.g., I-125 HSA) can be used to measure plasma volume, not specifically RBC volume.

Q: The primary site of vasopressin synthesis is

Supraoptic nucleus. ***Supraoptic nucleus*** - The **supraoptic nucleus** of the hypothalamus is the **primary site** for the synthesis of **vasopressin** (also known as antidiuretic hormone or ADH). - Approximately **80% of vasopressin** is produced by the neurosecretory cells in this nucleus. - The synthesized vasopressin is transported down axons to the posterior pituitary for storage and release. *Preoptic nucleus* - The **preoptic nucleus** is involved in various homeostatic functions, including **thermoregulation** and **sleep regulation**, but not the synthesis of vasopressin. - While it has neuronal connections to the hypothalamus, it does not produce ADH. *Paraventricular nucleus* - The **paraventricular nucleus** also synthesizes **both vasopressin and oxytocin**, accounting for approximately **20% of vasopressin production**. - While it does produce vasopressin, the **supraoptic nucleus remains the primary site**, making it the correct answer to this question. - The PVN also plays important roles in stress response and various autonomic functions. *Posterior pituitary* - The **posterior pituitary** (neurohypophysis) is responsible for the **storage and release** of vasopressin and oxytocin, not their synthesis. - These hormones are produced in the hypothalamic nuclei (supraoptic and paraventricular) and then transported down axonal tracts to the posterior pituitary.

Question 1

Glucose oxidase converts glucose to?

Accepted Answer

Gluconic acid

Answer

Glucuronic acid

Answer

Galactonic acid

Answer

Iduronic acid

Question 2

Which of the following is required for fatty acid synthesis ?

Accepted Answer

NADPH

Answer

NADH

Answer

FADH₂

Answer

None of the options

Question 3

Which hormone inhibits hormone-sensitive lipase?

Accepted Answer

Insulin

Answer

GH

Answer

ACTH

Answer

Thyroid hormone

Question 4

Which of the following is a tripeptide?

Accepted Answer

Glutathione

Answer

Angiotensin

Answer

Glucagon

Answer

Oxytocin

Question 5

What is the primary mechanism by which epinephrine reduces insulin secretion?

Accepted Answer

Predominantly through alpha action

Answer

Predominantly through beta action

Answer

Through both alpha and beta actions

Answer

Through muscarinic receptors

Question 6

Insulin is essential for glucose entry in?

Accepted Answer

Muscle cells

Answer

Beta cells of pancreas

Answer

Cortical neurons

Answer

Renal tubular cells

Question 7

Substance that is completely reabsorbed from the kidney?

Accepted Answer

Glucose

Answer

Na+

Answer

K+

Answer

Urea

Question 8

Which isotope is used to measure RBC volume?

Accepted Answer

Cr 51

Answer

H-3

Answer

D2O

Answer

I-135

Question 9

The primary site of vasopressin synthesis is

Accepted Answer

Supraoptic nucleus

Answer

Preoptic nucleus

Answer

Paraventricular nucleus

Answer

Posterior pituitary

Question 10

During moderate exercise, the respiratory rate increases in response to which of the following?

Accepted Answer

Increased PCO2 in arterial blood

Answer

Proprioceptive feedback from muscle spindles

Answer

Decreased PO2 in arterial blood

Answer

Stimulation of J-receptors

NEET-PG 2012

Biochemistry

Pharmacology

Physiology