NEET-PG 2015 Practice Questions

Q: Which of the following is not a derivative of foregut?

Cecum. ***Cecum*** - The **cecum** and the entire large intestine (except the distal third of the transverse colon) are derivatives of the **midgut** [1]. - The midgut is supplied by the **superior mesenteric artery**, differentiating it developmentally from the foregut. *First part of the duodenum* - The **first part of the duodenum** (from the pylorus to the major duodenal papilla) is derived from the **foregut**. - This section receives its blood supply from branches of the **celiac trunk**, consistent with its foregut origin. *Liver* - The **liver** develops as a budding from the distal foregut and is therefore a **foregut derivative** [2]. - It plays a crucial role in metabolism and detoxification, consistent with its early development from this segment. *Pancreas* - The **pancreas** develops from dorsal and ventral buds of the distal foregut, making it a **foregut derivative**. - Both its exocrine and endocrine functions are vital for digestion and glucose homeostasis.

Q: Amide group is present in which part of protein?

Peptide bond. ***Peptide bond*** - A **peptide bond** is formed between the **carboxyl group** of one amino acid and the **amino group** of another, releasing a water molecule. This bond has an **amide structure**. - The repeated formation of these amide (peptide) bonds links amino acids into long chains, forming a **polypeptide** or protein. *Amino-terminal* - The **amino-terminal (N-terminal)** end of a protein contains a free **amino group (-NH2)**, which is not part of an amide linkage within the polypeptide backbone. - It marks the beginning of the polypeptide chain and is typically involved in various cellular interactions and modifications. *Disulfide bond* - A **disulfide bond** is a covalent bond formed between two **sulfhydryl groups (-SH)** of **cysteine residues**, leading to the formation of a **cystine** residue. - This bond is crucial for stabilizing the **tertiary and quaternary structures** of proteins, but it does not contain an amide group. *Carboxy-terminal* - The **carboxy-terminal (C-terminal)** end of a protein contains a free **carboxyl group (-COOH)**, which is not part of an amide linkage within the polypeptide backbone. - It marks the end of the polypeptide chain and plays roles in protein processing, targeting, and regulation.

Q: What is the respiratory quotient of carbohydrates?

1. ***Option: 1 (Correct Answer)*** - The **respiratory quotient (RQ)** is the ratio of **carbon dioxide produced to oxygen consumed** during metabolism. - For carbohydrates, complete oxidation yields equal moles of CO2 and O2, resulting in an **RQ of 1.0**. - Example: C6H12O6 + 6O2 → 6CO2 + 6H2O, giving RQ = 6CO2/6O2 = 1.0 - This value reflects that carbohydrates are highly oxygenated molecules, requiring less external oxygen for their oxidation relative to the CO2 produced. *Option: 0.5* - An RQ of 0.5 is not observed for any major macronutrient during complete oxidation. - This value would imply significantly lower CO2 production relative to O2 consumption, which doesn't match any physiological substrate metabolism. *Option: 0.8* - An RQ of approximately 0.8 is characteristic of a **mixed diet** or the average value sometimes cited for **protein metabolism**. - Protein RQ typically ranges from 0.8-0.85, as proteins require more oxygen for their oxidation compared to the CO2 produced. - The exact RQ can vary depending on the specific amino acids being metabolized. *Option: 0.75* - An RQ around 0.7-0.75 may represent **fat-predominant metabolism** or a mixed diet with fats and carbohydrates. - Pure **fat metabolism** has an RQ of approximately **0.7**, as fats require substantial oxygen for oxidation due to their lower oxygen content relative to carbon and hydrogen. - Fats contain many C-H bonds and few C-O bonds, necessitating more oxygen for complete combustion.

Q: Which of the following enzyme activity decreases in fasting?

Phosphofructokinase I. ***Phosphofructokinase I*** - **Phosphofructokinase I (PFK-1)** activity **decreases** during fasting due to **decreased insulin-to-glucagon ratio**, which reduces **fructose-2,6-bisphosphate (F-2,6-BP)** levels, a powerful allosteric activator of PFK-1. - This reduction in activity slows down **glycolysis**, conserving glucose for critical tissues like the brain and redirecting metabolism toward **gluconeogenesis**. - **PFK-1 is the rate-limiting enzyme of glycolysis**, making its regulation particularly significant in the fasted state. *Hormone sensitive lipase* - **Hormone sensitive lipase (HSL)** activity **increases** during fasting due to elevated **glucagon** and **epinephrine** levels, which stimulate its phosphorylation via **protein kinase A (PKA)**. - This increased activity promotes the breakdown of stored **triglycerides** in adipose tissue, releasing **fatty acids** for β-oxidation and energy production. *Glycogen phosphorylase* - **Glycogen phosphorylase** activity **increases** during fasting, primarily stimulated by **glucagon** and **epinephrine**, leading to the breakdown of **glycogen** stores. - This enzyme is crucial for **glycogenolysis**, providing glucose to maintain blood sugar levels when dietary intake is absent. *Acetyl CoA Carboxylase* - **Acetyl CoA Carboxylase (ACC)** activity also **decreases** during fasting, as it is inhibited by **phosphorylation** mediated by **AMP-activated protein kinase (AMPK)** and **protein kinase A (PKA)**. - This reduction in activity inhibits **fatty acid synthesis**, shifting metabolism towards fatty acid **oxidation** for energy production. - **Note:** While ACC activity does decrease during fasting, **PFK-1** is considered the primary answer as it represents the key regulatory point for **glucose metabolism** (glycolysis vs. gluconeogenesis), which is the central metabolic shift during fasting.

Q: Which of the following cell types is considered insulin-dependent?

Myocytes. ***Myocytes*** - **Myocytes** (skeletal muscle cells) are **insulin-dependent** and represent the **largest site of insulin-mediated glucose disposal** in the body - Insulin promotes translocation of **GLUT4 transporters** to the cell membrane, enabling glucose uptake - Skeletal muscle accounts for approximately **70-80% of postprandial glucose disposal**, making it the most quantitatively significant insulin-dependent tissue *Adipocytes* - **Adipocytes** (fat cells) are also **insulin-dependent** and utilize **GLUT4 transporters** for glucose uptake - Insulin stimulates glucose uptake and conversion to triglycerides for storage - However, adipose tissue accounts for only **10-15% of glucose disposal**, making it less quantitatively significant than skeletal muscle - Both myocytes and adipocytes are considered the two major insulin-dependent tissues in the body *Pituitocytes* - **Pituitocytes** are supporting cells in the pituitary gland - They use **insulin-independent glucose transporters** (GLUT1/GLUT3) - The pituitary gland requires constant glucose supply independent of insulin status *RBCs* - **Red blood cells** lack mitochondria and depend entirely on **anaerobic glycolysis** - Glucose uptake occurs via **insulin-independent GLUT1 transporters** - RBCs must maintain glucose uptake at all times, regardless of insulin levels

Q: What is the typical pH range of intracellular fluid (ICF) compared to extracellular fluid (ECF)?

Typically around 7.0, slightly less than ECF. ***Typically around 7.0, slightly less than ECF*** - The **intracellular fluid (ICF)** tends to be slightly more acidic due to metabolic processes within cells that produce **acidic byproducts**. - This makes its pH typically around **7.0–7.2**, which is subtly lower than the extracellular fluid. *Typically around 7.4, slightly more than ICF* - A pH of approximately **7.4** is characteristic of **extracellular fluid (ECF)**, which includes plasma and interstitial fluid. - The ECF is maintained within a **narrow, slightly alkaline** range to support cellular function and enzyme activity throughout the body. *Approximately equal to ECF* - While both fluid compartments are maintained within a **narrow physiological range**, their pH values are not exactly equal. - This slight difference is essential for various biological processes, including maintaining **membrane potential** and **enzyme efficiency**. *Significantly higher than ECF* - The ICF pH is **not significantly higher** than ECF; in fact, it is slightly lower. - Maintaining too high a pH intracellularly would disrupt **cellular metabolism** and **protein structure**.

Q: Which of the following statements about ENaC is incorrect?

Composed of 2 homologous subunits. ***Composed of 2 homologous subunits*** - ENaC (Epithelial Sodium Channel) is a **heterotrimeric complex** composed of **three distinct subunits**: α, β, and γ. - The functional channel typically has a stoichiometry of 2α:1β:1γ, forming a heterotrimer. - These subunits share sequence homology but are **non-identical proteins**, not just two homologous subunits. - A fourth related subunit (δ) exists and can substitute for α in some tissues, but the classical ENaC is a three-subunit channel. *Epithelial channel* - ENaC is indeed an **epithelial channel** responsible for critical **sodium reabsorption** in various epithelia. - It plays a vital role in regulating **fluid and electrolyte balance** across tight epithelial layers. *Present in kidney and GIT* - ENaC is abundantly expressed in the **distal nephron of the kidney**, specifically in the collecting duct, where it mediates fine-tuning of sodium reabsorption. - It is also present in the **lower gastrointestinal tract (colon)**, contributing to sodium absorption, and in the airways and salivary glands. *Inhibited by amiloride* - **Amiloride** is a well-known **potassium-sparing diuretic** that specifically acts by blocking ENaC. - This inhibition reduces sodium reabsorption and, consequently, water reabsorption, leading to increased diuresis.

Q: What is the composition of epithelial sodium channels?

1α, 1β, 1γ. ***1α, 1β, 1γ*** - Epithelial sodium channels (**ENaCs**) are heterotrimeric complexes composed of one **alpha (α)**, one **beta (β)**, and one **gamma (γ) subunit**. - This specific subunit composition is essential for the channel's proper function in **sodium reabsorption** across epithelial tissues. *2α, 1β* - This composition is incomplete as it lacks the **gamma (γ) subunit**, which is a crucial component of the functional ENaC. - While alpha and beta subunits are present, the absence of the gamma subunit would impair the channel's ability to efficiently transport sodium. *2α, 1β, 2γ* - This composition is incorrect because a functional ENaC typically includes only **one gamma (γ) subunit**, not two. - An imbalance in subunit stoichiometry can lead to misfolding or improper assembly, affecting channel function. *2α, 1β, 1γ* - This combination correctly includes all three types of subunits (alpha, beta, gamma) but incorrectly states there are **two alpha (α) subunits**. - A functional ENaC has a single alpha subunit, making this option incorrect.

Q: What is the process of passive transport of molecules through protein pores/channels in the cell membrane?

Diffusion. ***Diffusion*** - **Diffusion** is the net movement of particles from an area of higher concentration to an area of lower concentration without requiring energy. - When diffusion occurs through **protein channels or pores** in the cell membrane, it is specifically termed **facilitated diffusion** or **channel-mediated diffusion**. - This remains a form of **passive transport** as it moves substances down their concentration gradient without ATP expenditure. - Examples include ion channels (Na⁺, K⁺, Ca²⁺) and aquaporins for water transport. *Active transport* - **Active transport** requires energy (typically ATP) to move substances **against** their concentration gradient. - It involves carrier proteins (pumps) like Na⁺-K⁺ ATPase that undergo conformational changes. - This is fundamentally different from passive transport through pores. *Transcytosis* - **Transcytosis** is a vesicular transport mechanism for moving substances across an entire cell. - It combines **endocytosis** on one side and **exocytosis** on the other side. - This is not passive transport through pores but rather bulk transport. *Endocytosis* - **Endocytosis** involves engulfing extracellular substances by forming membrane-bound vesicles. - Types include phagocytosis, pinocytosis, and receptor-mediated endocytosis. - This requires energy and does not involve transport through pores.

Q: Which transport process is mediated by carriers and occurs against the concentration gradient?

Active transport. ***Active transport*** - **Active transport** systems use carrier proteins to move molecules across a membrane **against their concentration gradient**, requiring **metabolic energy** (e.g., from ATP hydrolysis). - This process is crucial for maintaining cellular homeostasis, accumulating specific substances, and establishing ion gradients. *Facilitated diffusion* - **Facilitated diffusion** also uses **carrier proteins**, but it moves substances **down their concentration gradient**, thus **not requiring metabolic energy**. - It increases the rate of diffusion for molecules that cannot easily cross the lipid bilayer, like glucose. *Osmosis* - **Osmosis** is the movement of **water molecules** across a selectively permeable membrane **down their water potential gradient**, driven by solute concentration differences, and does **not involve carrier proteins**. - This process equalizes solute concentrations on both sides of the membrane. *Endocytosis* - **Endocytosis** is a bulk transport mechanism where cells **engulf substances** from outside by forming vesicles from the plasma membrane; it's a form of active transport but **does not typically involve specific carrier proteins** embedded in the membrane for individual molecules. - This process is used for taking in larger molecules, particles, or even other cells.

Question 1

Which of the following is not a derivative of foregut?

Accepted Answer

Cecum

Answer

Liver

Answer

Pancreas

Answer

First part of the duodenum

Question 2

Amide group is present in which part of protein?

Accepted Answer

Peptide bond

Answer

Amino-terminal

Answer

Disulfide bond

Answer

Carboxy-terminal

Question 3

What is the respiratory quotient of carbohydrates?

Accepted Answer

1

Answer

0.5

Answer

0.8

Answer

0.75

Question 4

Which of the following enzyme activity decreases in fasting?

Accepted Answer

Phosphofructokinase I

Answer

Hormone sensitive lipase

Answer

Glycogen phosphorylase

Answer

Acetyl CoA Carboxylase

Question 5

Which of the following cell types is considered insulin-dependent?

Accepted Answer

Myocytes

Answer

Pituitocytes

Answer

Adipocytes

Answer

RBCs

Question 6

What is the typical pH range of intracellular fluid (ICF) compared to extracellular fluid (ECF)?

Accepted Answer

Typically around 7.0, slightly less than ECF

Answer

Typically around 7.4, slightly more than ICF

Answer

Approximately equal to ECF

Answer

Significantly higher than ECF

Question 7

Which of the following statements about ENaC is incorrect?

Accepted Answer

Composed of 2 homologous subunits

Answer

Present in kidney and GIT

Answer

Epithelial channel

Answer

Inhibited by amiloride

Question 8

What is the composition of epithelial sodium channels?

Accepted Answer

1α, 1β, 1γ

Answer

2α, 1β, 1γ

Answer

2α, 1β

Answer

2α, 1β, 2γ

Question 9

What is the process of passive transport of molecules through protein pores/channels in the cell membrane?

Accepted Answer

Diffusion

Answer

Transcytosis

Answer

Endocytosis

Answer

Active transport

Question 10

Which transport process is mediated by carriers and occurs against the concentration gradient?

Accepted Answer

Active transport

Answer

Facilitated diffusion

Answer

Osmosis

Answer

Endocytosis

NEET-PG 2015

Anatomy

Biochemistry

Physiology