NEET-PG 2013 - Biochemistry Practice Questions

Q: What is the primary reason for the detergent action of bile salts?

Amphipathic nature. ***Amphipathic nature*** - Bile salts are **amphipathic molecules**, meaning they have both **hydrophilic (water-loving)** and **hydrophobic (water-fearing)** regions. - This dual nature allows them to emulsify fats by surrounding lipid droplets with their hydrophobic ends dissolving in the fat and their hydrophilic ends facing the aqueous environment, stabilizing the emulsion. *Hydrophobic properties* - While bile salts do possess **hydrophobic regions**, these alone are not sufficient for detergent action. - The ability to interact with both oil and water phases simultaneously is crucial for their role in **emulsification**. *Acts as a zwitterion* - A zwitterion is a molecule with both a **positive and negative charge**, but an overall neutral charge. - This property is not the primary mechanism behind the **detergent action** of bile salts, which relies more on their ability to solubilize fats. *None of the options* - The **amphipathic nature** is indeed the primary reason for the detergent action; therefore, this option is incorrect.

Q: Glucagon stimulates

Gluconeogenesis. ***Gluconeogenesis*** - **Glucagon** is a hormone that primarily acts to raise **blood glucose levels** by stimulating the production of glucose from non-carbohydrate sources. - This process, **gluconeogenesis**, occurs mainly in the liver and is initiated by glucagon to counteract hypoglycemia. *Glycogenesis* - **Glycogenesis** is the process of synthesizing **glycogen** from glucose and is primarily stimulated by insulin when blood glucose levels are high. - Glucagon's role is to *inhibit* glycogen synthesis and instead promote glycogen breakdown. *Fatty acid synthesis* - **Fatty acid synthesis** is an anabolic process that primarily occurs when there is an excess of energy and glucose, often stimulated by **insulin**. - Glucagon generally has an **inhibitory effect** on fatty acid synthesis, as its main goal is to mobilize energy stores, not create them. *Glycolysis* - **Glycolysis** is the breakdown of glucose to produce energy, and it is stimulated when glucose is abundant and energy is needed. - Glucagon primarily acts to *inhibit* glycolysis in the liver, thereby conserving glucose for use by other tissues and promoting its release into the bloodstream.

Q: What is the unit for a prolactin level of 20 in blood?

ng/ml. ***ng/ml*** - Prolactin levels in blood are typically measured in **nanograms per milliliter (ng/mL)**, reflecting the very small concentrations of hormones. - A value of 20 ng/mL falls within the typical reference range for prolactin. *mg/mL* - **Milligrams per milliliter (mg/mL)** is a unit used for much higher concentrations, more common for drugs or larger molecules, not hormones like prolactin. - If prolactin were measured in mg/mL, a value of 20 mg/mL would be an astronomically high and physiologically impossible level. *mg/L* - **Milligrams per liter (mg/L)** is also a unit for higher concentrations than those typically seen for hormones in blood. - 20 mg/L is equivalent to 20 µg/mL or 20,000 ng/mL, which would indicate severe hyperprolactinemia. *ng/L* - **Nanograms per liter (ng/L)** is a unit for extremely low concentrations. - A reading of 20 ng/L would be too low for normal physiological prolactin levels, as 1 ng/mL equals 1000 ng/L.

Q: Which of the following is not an androgen?

17α-hydroxyprogesterone. ***17α-hydroxyprogesterone*** - This is a **progesterone derivative** and an intermediate in the synthesis of androgens and corticosteroids, but it does **not possess significant androgenic activity** itself. - Its primary role is as a precursor, rather than a direct androgen. *Testosterone* - **Testosterone** is the **primary male sex hormone** and a potent androgen, responsible for the development of male secondary sexual characteristics. - It plays crucial roles in muscle mass, bone density, libido, and erythropoiesis. *Dihydrotestosterone* - **Dihydrotestosterone (DHT)** is a potent androgen, formed from testosterone by the enzyme 5α-reductase. - DHT is responsible for the development of external male genitalia during fetal development and contributes to prostate growth and male pattern baldness in adults. *Androstenedione* - **Androstenedione** is a **weak androgen** and an important **precursor hormone** in the biosynthesis of testosterone and estrogens. - It is produced in the adrenal glands and gonads, serving as an intermediate step in steroidogenesis.

Q: Carbonic anhydrase activity is found in all of the following except?

Plasma. ***Plasma*** - **Carbonic anhydrase** is an intracellular enzyme that catalyzes the rapid interconversion of carbon dioxide and water to carbonic acid, **bicarbonate**, and protons. - It is notably **absent in plasma** in healthy individuals, as it is primarily found within cells where its function is crucial for pH regulation and CO2 transport. *Brain* - Carbonic anhydrase is found in various brain cells, including **neurons**, **oligodendrocytes**, and **astrocytes**. - It plays a vital role in pH regulation, fluid balance, and the production of cerebrospinal fluid (CSF) within the **central nervous system**. *Kidney* - The kidney is rich in carbonic anhydrase, particularly in the **proximal tubules** and collecting ducts. - It is critical for **bicarbonate reabsorption** and proton excretion, essential processes for maintaining acid-base balance. *RBC* - **Red blood cells (RBCs)** contain a high concentration of carbonic anhydrase (specifically CA-I and CA-II isoforms). - This enzyme facilitates the rapid conversion of CO2 to bicarbonate for transport to the lungs and the reverse reaction for **CO2 exhalation**.

Q: What is the approximate half-life of albumin in the human body?

20 days. ***20 days*** - The **half-life of albumin** in the human body is approximately **20 days**, reflecting the time it takes for half of the circulating albumin to be catabolized or excreted. - This relatively long half-life means that changes in albumin levels, such as those due to malnutrition or liver disease, may take several weeks to become evident. *3 days* - A half-life of 3 days is too short for albumin, which is a major, long-lasting plasma protein. - Proteins with such a short half-life typically include more rapidly turnover proteins or small peptides. *7 days* - A half-life of 7 days is also too short for albumin, which plays a critical role in maintaining plasma oncotic pressure and transporting various substances. - While some proteins have a 7-day half-life, albumin's is considerably longer. *30 days* - A half-life of 30 days is longer than the typical half-life of albumin. - While some proteins may have half-lives in this range, 20 days is the more commonly accepted value for albumin.

Q: What is the half-life of Prealbumin?

2 days. ***2 days*** - Prealbumin, also known as transthyretin, has a **short half-life** of approximately 2-3 days, making it a sensitive indicator of recent changes in **nutritional status**. - Its rapid turnover allows for prompt reflection of improvement or deterioration in protein synthesis. *10 days* - A half-life of 10 days would make prealbumin less responsive to acute changes in nutrition compared to its actual turnover rate. - This duration is longer than the typical half-life of proteins used to monitor **short-term nutritional status**. *20 days* - A 20-day half-life would indicate a protein with a much slower turnover, unsuitable for monitoring **acute nutritional interventions**. - Proteins with such long half-lives, like **albumin**, reflect more chronic states rather than rapid changes. *40 days* - A half-life of 40 days is characteristic of proteins like **albumin**, which are influenced by longer-term nutritional and inflammatory processes. - Such a long half-life would not be useful for assessing immediate responses to **nutritional support** or acute disease states.

Q: Which of the following is activated by calmodulin?

Calcium/calmodulin-dependent protein kinase. ***Calcium/calmodulin-dependent protein kinase*** - **Calmodulin** is a **calcium-binding messenger protein** that, when bound to calcium, undergoes a conformational change allowing it to activate various enzymes, including **calcium/calmodulin-dependent protein kinases** (CaMKs). - CaMKs play crucial roles in many cellular processes, including **metabolism**, **gene expression**, and **neurotransmission**, by phosphorylating target proteins. *Muscle phosphorylase* - **Muscle phosphorylase** (glycogen phosphorylase) is primarily activated by **epinephrine**, **AMP**, and **nerve stimulation** (via calcium), but not directly by calmodulin. - Its activation leads to the breakdown of **glycogen** into glucose-1-phosphate. *Phospholipase C* - **Phospholipase C (PLC)** is typically activated by **G protein-coupled receptors** and **tyrosine kinase receptors**, leading to the production of **inositol trisphosphate (IP3)** and **diacylglycerol (DAG)**. - While it plays a role in calcium signaling upstream (releasing calcium from stores), it is not directly activated by calmodulin. *Adenylyl cyclase* - **Adenylyl cyclase (AC)** is a key enzyme in generating **cyclic AMP (cAMP)**, and is commonly regulated by **G proteins** (specifically Gs and Gi subunits). - While certain isoforms (AC1, AC3, AC8) can be directly activated by calcium/calmodulin, **CaMK** remains the most classical and direct example of calmodulin activation.

Q: What is the normal range of ferritin levels in adult males?

30-300 ng/ml. ***30-300 ng/ml*** - The normal range for **ferritin levels** in adult males is typically **30-300 ng/ml** (some laboratories report 30-400 ng/ml). - Ferritin is an **iron storage protein**, and its levels reflect the body's iron stores. - Values below 30 ng/ml suggest **iron deficiency**, while values above 300 ng/ml may indicate iron overload or inflammatory conditions. *10-20 ng/ml* - These levels are **significantly low** and indicate **iron deficiency**. - This range is well below the normal threshold and would warrant investigation and likely iron supplementation. - Levels below 15 ng/ml are diagnostic of **iron deficiency** even in the absence of anemia. *300-500 ng/ml* - Levels in this range are considered **elevated** and can indicate iron overload, chronic inflammation, liver disease, or malignancy. - While some laboratories extend the upper limit to 400 ng/ml, persistent elevation above 300 ng/ml warrants further investigation. - Common causes include **hemochromatosis**, **chronic liver disease**, or **inflammatory conditions**. *500-700 ng/ml* - These levels are **significantly elevated** and strongly suggest **iron overload conditions** such as **hemochromatosis**, severe inflammatory states, or hepatocellular injury. - High ferritin levels can be associated with organ damage, leading to conditions like **cirrhosis** or **cardiomyopathy**. - Requires urgent investigation to identify the underlying cause.

Question 1

What is the primary reason for the detergent action of bile salts?

Accepted Answer

Amphipathic nature

Answer

Hydrophobic properties

Answer

Acts as a zwitterion

Answer

None of the options

Question 2

Glucagon stimulates

Accepted Answer

Gluconeogenesis

Answer

Glycogenesis

Answer

Fatty acid synthesis

Answer

Glycolysis

Question 3

What is the unit for a prolactin level of 20 in blood?

Accepted Answer

ng/ml

Answer

mg/ml

Answer

mg/l

Answer

ng/l

Question 4

Which of the following is not an androgen?

Accepted Answer

17α-hydroxyprogesterone

Answer

Testosterone

Answer

Dihydrotestosterone

Answer

Androstenedione

Question 5

Carbonic anhydrase activity is found in all of the following except?

Accepted Answer

Plasma

Answer

Brain

Answer

Kidney

Answer

RBC

Question 6

What is the approximate half-life of albumin in the human body?

Accepted Answer

20 days

Answer

30 days

Answer

3 days

Answer

7 days

Question 7

What is the half-life of Prealbumin?

Accepted Answer

2 days

Answer

10 days

Answer

20 days

Answer

40 days

Question 8

Which of the following is activated by calmodulin?

Accepted Answer

Calcium/calmodulin-dependent protein kinase

Answer

Muscle phosphorylase

Answer

Phospholipase C

Answer

Adenylyl cyclase

Question 9

Which of the following statements about G protein-coupled receptors (GPCRs) is true?

Accepted Answer

G proteins can act as either inhibitory or excitatory based on the type of alpha subunit.

Answer

The three subunits alpha, beta, and gamma must remain together as a complex for G protein to function.

Answer

G proteins bind directly to hormones to become activated.

Answer

In the resting state, G proteins are bound to GTP.

Question 10

What is the normal range of ferritin levels in adult males?

Accepted Answer

30-300 ng/ml

Answer

300-500 ng/ml

Answer

10-20 ng/ml

Answer

500-700 ng/ml

NEET-PG 2013 — Biochemistry