Which of the following plant components is not fermented by gastrointestinal microorganisms?
What is the primary reason for the detergent action of bile salts?
Glucagon stimulates
What is the unit for a prolactin level of 20 in blood?
Trypsinogen is converted to trypsin by?
In type IA Maple Syrup Urine Disease, which gene mutation is responsible?
Which element is required by phosphofructokinase?
What is the half-life of Prealbumin?
Which of the following is activated by calmodulin?
What is the approximate half-life of albumin in the human body?
NEET-PG 2013 - Biochemistry NEET-PG Practice Questions and MCQs
Question 11: 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 12: 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 13: 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.
Question 14: What is the unit for a prolactin level of 20 in blood?
- A. ng/ml (Correct Answer)
- B. mg/ml
- C. mg/l
- D. ng/l
Explanation: ***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.
Question 15: 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 16: In type IA Maple Syrup Urine Disease, which gene mutation is responsible?
- A. BCKDHB
- B. DBT
- C. DLD
- D. BCKDHA (Correct Answer)
Explanation: ***BCKDHA*** - **Maple Syrup Urine Disease (MSUD)** type IA is caused by a mutation in the **BCKDHA gene**, which codes for the E1α subunit of the **branched-chain α-keto acid dehydrogenase (BCKD) complex**. - This **enzyme complex** is crucial for the metabolism of **branched-chain amino acids (BCAAs)**: leucine, isoleucine, and valine. *BCKDHB* - The **BCKDHB gene** codes for the E1β subunit of the **BCKD complex**. - Mutations in **BCKDHB** are associated with **type IB MSUD**, not type IA. *DBT* - The **DBT gene** codes for the E2 subunit (dihydrolipoyl transacylase) of the **BCKD complex**. - Mutations in **DBT** are responsible for **type II MSUD**. *DLD* - The **DLD gene** codes for the E3 subunit (dihydrolipoyl dehydrogenase), which is a component shared by several **α-keto acid dehydrogenase complexes**. - Mutations in the **DLD gene** lead to **type III MSUD** and other pyruvate dehydrogenase complex deficiencies, rather than type IA.
Question 17: 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 18: What is the half-life of Prealbumin?
- A. 2 days (Correct Answer)
- B. 10 days
- C. 20 days
- D. 40 days
Explanation: ***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.
Question 19: Which of the following is activated by calmodulin?
- A. Muscle phosphorylase
- B. Calcium/calmodulin-dependent protein kinase (Correct Answer)
- C. Phospholipase C
- D. Adenylyl cyclase
Explanation: ***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.
Question 20: 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.