What is the primary reason for the detergent action of bile salts?
What is the approximate half-life of albumin in the human body?
Which of the following plant components is not fermented by gastrointestinal microorganisms?
Which element is required by phosphofructokinase?
Which of the following statements about G protein-coupled receptors (GPCRs) is true?
Which of the following is not an androgen?
What is the normal range of ferritin levels in adult males?
Which protein hormone is often referred to as the 'guardian angel against obesity' due to its role in regulating metabolism?
Trypsinogen is converted to trypsin by?
Glucagon stimulates
NEET-PG 2013 - Biochemistry NEET-PG Practice Questions and MCQs
Question 11: What is the primary reason for the detergent action of bile salts?
- A. Hydrophobic properties
- B. Acts as a zwitterion
- C. Amphipathic nature (Correct Answer)
- D. None of the options
Explanation: ***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.
Question 12: What is the approximate half-life of albumin in the human body?
- A. 30 days
- B. 20 days (Correct Answer)
- C. 3 days
- D. 7 days
Explanation: ***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.
Question 13: Which of the following plant components is not fermented by gastrointestinal microorganisms?
- A. Lignin (Correct Answer)
- B. Cellulose
- C. Hemicellulose
- D. Pectin
Explanation: ***Lignin*** - **Lignin** is a complex polymer found in plant cell walls that is highly resistant to degradation by digestive enzymes and microbial fermentation in the gastrointestinal tract. - Its complex, cross-linked structure makes it **non-fermentable** by the microorganisms typically present in the human gut. *Cellulose* - **Cellulose** is a major component of plant cell walls and is a type of dietary fiber that can be fermented by certain gut bacteria. - While humans lack the enzymes to digest cellulose, colonic microorganisms possess cellulases that break it down into **short-chain fatty acids (SCFAs)**. *Hemicellulose* - **Hemicellulose** is a diverse group of plant polysaccharides that are a significant source of fermentable fiber for gut microbiota. - It is readily broken down by gastrointestinal bacteria into **SCFAs** and gases, contributing to colonic health. *Pectin* - **Pectin** is a soluble dietary fiber found in fruits and vegetables, known for its gel-forming properties. - It is highly fermentable by gut microorganisms, leading to the production of **SCFAs** like butyrate, propionate, and acetate.
Question 14: Which element is required by phosphofructokinase?
- A. Magnesium (Correct Answer)
- B. Inorganic phosphate
- C. Manganese
- D. Copper
Explanation: **Magnesium** - **Phosphofructokinase** (PFK) is an enzyme in **glycolysis** that catalyzes the phosphorylation of fructose-6-phosphate. - This reaction requires **ATP**, and like many enzymes that utilize ATP, PFK requires **magnesium ions (Mg²⁺)** as a cofactor, typically forming a complex with ATP (MgATP²⁻). *Inorganic phosphate* - **Inorganic phosphate** is a substrate for some kinase reactions, but not a direct cofactor requirement for the *activation* of phosphofructokinase itself. - While phosphate is incorporated into molecules during phosphorylation, it does not act as a metal ion cofactor to facilitate the enzyme's activity. *Manganese* - While **manganese (Mn²⁺)** can sometimes substitute for magnesium in certain enzyme reactions, it is not the primary or required cofactor for phosphofructokinase under normal physiological conditions. - Many enzymes have a preference for specific metal ions based on their active site structure and coordination chemistry. *Copper* - **Copper (Cu²⁺)** is a cofactor for a variety of enzymes, particularly those involved in **redox reactions** (e.g., cytochrome c oxidase, superoxide dismutase). - However, copper is not a required metallic cofactor for the activity of **phosphofructokinase** in glycolysis.
Question 15: Which of the following statements about G protein-coupled receptors (GPCRs) is true?
- A. The three subunits alpha, beta, and gamma must remain together as a complex for G protein to function.
- B. G proteins can act as either inhibitory or excitatory based on the type of alpha subunit. (Correct Answer)
- C. G proteins bind directly to hormones to become activated.
- D. In the resting state, G proteins are bound to GTP.
Explanation: ***G proteins can act as either inhibitory or excitatory based on the type of alpha subunit.*** - Different classes of Gα subunits (e.g., **Gαs**, **Gαi**, **Gαq**) couple to diverse downstream effectors, leading to either **stimulation** (excitatory) or **inhibition** of cellular processes. - For example, **Gαs** activates adenylyl cyclase, while **Gαi** inhibits it, demonstrating their opposing roles. *The three subunits alpha, beta, and gamma must remain together as a complex for G protein to function.* - Upon activation, the **Gα subunit dissociates** from the **Gβγ dimer**, and both free units can then independently modulate effector molecules. - For the G protein to function in signal transduction, the α subunit often separates from the βγ dimer to interact with its target enzyme or ion channel. *G proteins bind directly to hormones to become activated.* - **GPCRs** (the receptors themselves) bind to hormones or other ligands on the **extracellular side** of the membrane. - The binding of the ligand to the GPCR induces a conformational change in the receptor, which then activates the associated G protein on the intracellular side. *In the resting state, G proteins are bound to GTP.* - In the **resting (inactive) state**, the Gα subunit of the trimeric G protein is bound to **GDP**. - Activation occurs when the GPCR facilitates the exchange of **GDP for GTP** on the Gα subunit.
Question 16: Which of the following is not an androgen?
- A. 17α-hydroxyprogesterone (Correct Answer)
- B. Testosterone
- C. Dihydrotestosterone
- D. Androstenedione
Explanation: ***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.
Question 17: What is the normal range of ferritin levels in adult males?
- A. 30-300 ng/ml (Correct Answer)
- B. 300-500 ng/ml
- C. 10-20 ng/ml
- D. 500-700 ng/ml
Explanation: ***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 18: Which protein hormone is often referred to as the 'guardian angel against obesity' due to its role in regulating metabolism?
- A. Adiponectin (Correct Answer)
- B. Fibronectin
- C. High-Density Lipoprotein (HDL)
- D. Insulin
Explanation: ***Adiponectin*** - **Adiponectin** is a hormone secreted by **adipose tissue** that plays a crucial role in regulating glucose and fatty acid metabolism, increasing **insulin sensitivity**, and decreasing inflammation. - Its levels are inversely correlated with body fat percentage; individuals with obesity tend to have lower adiponectin levels, leading to its nickname as the 'guardian angel against obesity'. *Fibronectin* - **Fibronectin** is a glycoprotein involved in cell adhesion, growth, migration, and differentiation, and is a key component of the **extracellular matrix**. - It does not primarily function in metabolic regulation or body weight control, unlike adiponectin. *High-Density Lipoprotein (HDL)* - **HDL** is a type of lipoprotein that transports cholesterol from peripheral tissues back to the liver, a process known as **reverse cholesterol transport**. - While beneficial for cardiovascular health, HDL is a lipid-carrying particle, not a protein hormone, and its primary role is not in metabolic regulation or direct obesity prevention. *Insulin* - **Insulin** is a peptide hormone produced by the pancreas that regulates carbohydrate and fat metabolism, primarily by facilitating glucose uptake from the blood into cells. - While essential for metabolism, high levels of insulin in the context of insulin resistance can contribute to obesity, rather than act against it.
Question 19: Trypsinogen is converted to trypsin by?
- A. Combination of 2 molecules of trypsinogen
- B. Phosphorylation
- C. Addition of alkyl group
- D. Removal of specific amino acids from trypsinogen (Correct Answer)
Explanation: ***Removal of specific amino acids from trypsinogen*** - Trypsinogen is an **inactive zymogen** that is activated by the enzymatic cleavage of a **short N-terminal peptide**. - This cleavage event, primarily catalyzed by **enteropeptidase** (or trypsin itself), transforms trypsinogen into active **trypsin**, a process known as **proteolytic activation**. *Combination of 2 molecules of trypsinogen* - The activation of trypsinogen to trypsin is a **unimolecular conformational change** followed by proteolytic cleavage, not a combination reaction between two zymogen molecules. - While trypsin can activate other trypsinogen molecules, the initial activation does not involve the physical combination of two zymogen molecules. *Phosphorylation* - **Phosphorylation** is a common regulatory mechanism in proteins but is not the primary method for activating inactive trypsinogen. - Trypsinogen activation relies on a **proteolytic cleavage event**, rather than the addition of a phosphate group. *Addition of alkyl group* - The addition of an **alkyl group** is not a known mechanism for the physiological activation of trypsinogen. - Enzymatic activation typically involves **hydrolysis of peptide bonds** or other specific post-translational modifications.
Question 20: Glucagon stimulates
- A. Gluconeogenesis (Correct Answer)
- B. Glycogenesis
- C. Fatty acid synthesis
- D. Glycolysis
Explanation: ***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.