NEET-PG 2012 Practice Questions

Q: Which of the following cell types is neuroectodermal in origin?

Smooth muscle cells. ***Smooth muscle cells*** - This is the **correct answer** based on a **specific exception**: smooth muscle cells of the **iris dilator and sphincter muscles** and the **ciliary muscle** in the eye are derived from **neuroectoderm** (specifically from the **optic cup**, an outgrowth of the neural tube). - **Important note:** The vast majority of smooth muscle in the body is of **mesodermal origin** (e.g., in blood vessels, GI tract, respiratory tract). This question tests knowledge of this **notable embryological exception**. - In the context of the given options, this is the only cell type with any neuroectodermal component. *Skeletal muscle cells* - Skeletal muscle cells are entirely derived from the **paraxial mesoderm**, specifically from **somites** (myotome portion). - They form the voluntary muscles of the body and are **never** of neuroectodermal origin. *Endothelial cells* - Endothelial cells lining blood vessels and lymphatic vessels are derived from the **mesoderm** (specifically from **angioblasts**). - They are part of the cardiovascular system and are **entirely mesodermal** in origin. *Cardiac muscle cells* - Cardiac muscle cells are derived from the **splanchnic mesoderm** (lateral plate mesoderm). - The heart musculature is **entirely mesodermal** with no neuroectodermal contribution. **Clinical Pearl:** Classic neuroectodermal derivatives include neurons, glial cells (astrocytes, oligodendrocytes), ependymal cells, and neural crest derivatives (Schwann cells, melanocytes, chromaffin cells). The smooth muscle of the iris represents an important exception to the general rule that smooth muscle is mesodermal.

Q: Where does oxidative deamination primarily occur in the human body?

Mitochondria of liver cells. ***Mitochondria of liver cells*** - **Oxidative deamination**, particularly of glutamate, is a central process in **amino acid catabolism** and occurs predominantly in the **mitochondria of liver cells**. - This process is crucial for removing the **amino group (NH3)** from amino acids, forming ammonia, which is then detoxified into urea. *Cytoplasm of all cells* - While cells have cytoplasmic metabolic pathways, the primary enzyme for oxidative deamination, **glutamate dehydrogenase**, is located in the mitochondria. - The cytoplasm primarily handles glycolysis and various synthetic pathways, but not the bulk of oxidative deamination. *Mitochondria of all cells* - Although mitochondria are the site of oxidative metabolism in most cells, the **liver** is the main organ responsible for processing exogenous amino acids and their subsequent comprehensive deamination. - Other cells perform some amino acid metabolism, but not the large-scale oxidative deamination seen in the liver. *Cytoplasm of liver cells* - The cytoplasm of liver cells is involved in various metabolic processes, including gluconeogenesis and fatty acid synthesis. - However, the key enzymes for oxidative deamination are specifically compartmentalized within the **mitochondria** of these cells, not the cytoplasm.

Q: Which of the following substances does not inhibit glycolysis?

Fluoroacetate. ***Fluoroacetate*** - **Fluoroacetate** is not a direct inhibitor of glycolysis. Instead, it is metabolized to **fluorocitrate**, which then acts as an inhibitor of **aconitase** in the **Krebs cycle (TCA cycle)**, thereby affecting cellular respiration at a later stage. - Its primary role in metabolic inhibition is within the **mitochondria**, impacting energy production via the TCA cycle rather than the glycolytic pathway. *Fluoride* - **Fluoride** is a known inhibitor of **enolase**, an enzyme in the penultimate step of glycolysis. - It forms a complex with **magnesium** and **phosphate** to block the active site of enolase, preventing the conversion of 2-phosphoglycerate to phosphoenolpyruvate. *Arsenite* - **Arsenite** inhibits glycolysis by targeting enzymes containing **sulfhydryl (–SH) groups**, particularly **glyceraldehyde-3-phosphate dehydrogenase (GAPDH)**, a critical enzyme in the glycolytic pathway. - It also inhibits the **pyruvate dehydrogenase complex** (linking glycolysis to the TCA cycle) and TCA cycle enzymes like **α-ketoglutarate dehydrogenase**, thereby affecting multiple stages of cellular respiration. *Iodoacetate* - **Iodoacetate** is a potent inhibitor of the enzyme **glyceraldehyde-3-phosphate dehydrogenase (GAPDH)**. - It specifically alkylates the **cysteine residue** at the active site of GAPDH, preventing the conversion of glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate, thereby blocking glycolysis.

Q: Which tissue cannot convert glucose 6-phosphate to free glucose due to lack of glucose-6-phosphatase?

Muscle. ***Muscle*** - Muscle tissue lacks the enzyme **glucose-6-phosphatase**, which is essential for hydrolyzing glucose 6-phosphate back to **free glucose**. - Therefore, glucose 6-phosphate in muscle is primarily used for **glycolysis** (energy production) or stored as glycogen for local use. *Liver* - The liver contains **glucose-6-phosphatase**, allowing it to convert **glucose 6-phosphate** to **free glucose**. - This capability is crucial for maintaining **blood glucose homeostasis** and releasing glucose into circulation. *Adipose tissue* - Adipose tissue, like muscle, **lacks glucose-6-phosphatase** and cannot convert glucose 6-phosphate back to free glucose. - Glucose 6-phosphate in adipose tissue is primarily channeled into **fatty acid synthesis** and storage. *Kidney* - The kidney, particularly the renal cortex, possesses **glucose-6-phosphatase** and can convert glucose 6-phosphate to **free glucose**. - This contributes to **gluconeogenesis** and release of glucose into the blood, especially during fasting.

Q: At which positions does pancreatic lipase hydrolyze the ester linkages of triacylglycerides?

1 and 3. **Correct: 1 and 3** - Pancreatic lipase specifically targets the **ester bonds at the sn-1 and sn-3 positions** (primary alcohol positions) on the glycerol backbone of triacylglycerides. - This positional specificity results in the formation of **2-monoacylglycerol (2-MAG)** and **two free fatty acids**. - This is the characteristic action of pancreatic triacylglycerol lipase during fat digestion in the intestinal lumen. *Incorrect: 1 and 2* - Hydrolysis at positions 1 and 2 would produce a 3-monoacylglycerol and free fatty acids, which is not the physiological product of pancreatic lipase. - The enzyme's positional specificity favors the outer sn-1 and sn-3 positions, not the middle sn-2 position. *Incorrect: 2 and 3* - Hydrolysis at positions 2 and 3 would yield a 1-monoacylglycerol and free fatty acids, which does not reflect pancreatic lipase activity. - The enzyme specifically spares the sn-2 position due to its structural specificity. *Incorrect: Only 3* - If only position 3 were hydrolyzed, the product would be a 1,2-diacylglycerol and one free fatty acid. - This represents incomplete hydrolysis; pancreatic lipase typically hydrolyzes **both outer positions (sn-1 and sn-3)** due to its regiospecificity.

Q: Which type of fatty acids should be included in the diet to manage chyluria?

Medium-chain fatty acids. ***Medium-chain fatty acids*** - **Medium-chain fatty acids (MCFAs)** are absorbed directly into the **portal circulation** without being re-esterified to triglycerides or incorporated into chylomicrons [1]. This helps bypass the compromised lymphatic system. - In **chyluria**, the lymphatic system's integrity is disrupted, leading to leakage of **chyle** (lymphatic fluid rich in chylomicrons) into the urinary tract. MCFAs provide a source of fat that does not rely on the lymphatic pathway for transport [1]. *Short-chain fatty acids* - **Short-chain fatty acids (SCFAs)** are primarily produced by bacterial fermentation in the colon and are absorbed directly into the portal circulation. - While they do not rely on the lymphatic system, their dietary contribution as a significant energy source is limited, and they are not the primary fat source for patients with chyluria. *Long-chain fatty acids* - **Long-chain fatty acids (LCFAs)** are absorbed with the help of bile salts, re-esterified into triglycerides, and packaged into **chylomicrons** within the intestinal cells [2]. - These chylomicrons then enter the **lymphatic system** and eventually the bloodstream, which is precisely the pathway that is compromised in chyluria, making them unsuitable [2]. *Omega-3 fatty acids* - **Omega-3 fatty acids** are a type of **long-chain polyunsaturated fatty acid** that also follow the chylomicron-lymphatic pathway for absorption [3]. - While beneficial for other health aspects, they are not suitable for managing chyluria due to their reliance on the **lymphatic system** for transport, which is dysfunctional in this condition.

Q: What color is emitted by FITC after absorbing blue light?

Yellow-green. ***Yellow-green*** - Fluorescein isothiocyanate (FITC) is a common fluorochrome used in **fluorescence microscopy** and flow cytometry. - Upon excitation by blue light (typically around 495 nm), FITC emits light in the **yellow-green spectrum**, specifically around 521 nm. - This is the **spectroscopically accurate** description of FITC's emission peak. *Orange-red* - **Orange-red emission** is characteristic of fluorochromes like **phycoerythrin (PE)** or **Texas Red**, not FITC. - These fluorochromes have different **excitation and emission maxima** compared to FITC. *Apple-green* - While FITC fluorescence is sometimes clinically described as **"apple-green"** (especially in immunofluorescence), this is a **subjective visual description** rather than a precise spectral term. - The more **spectroscopically accurate** description is **yellow-green**, which reflects FITC's specific emission peak at 521 nm. - "Apple-green" typically suggests a purer green without the yellow component. *Golden-brown* - **Golden-brown** is not a typical emission color for fluorochromes like FITC. - This color is generally associated with **pigments** or stained tissues (e.g., lipofuscin, hemosiderin), not fluorescent probes.

Q: Nonshivering thermogenesis in adults is due to:

Brown fat between the shoulders. ***Brown fat between the shoulders*** - In adults, the primary **effector tissue** for **non-shivering thermogenesis** is **brown adipose tissue (BAT)**, with major depots located between the shoulders, around the neck, and along the spine. - **BAT** contains specialized mitochondria with **uncoupling protein 1 (UCP1)** that uncouples oxidative phosphorylation, generating heat instead of ATP. - This is the tissue where non-shivering thermogenesis actually occurs, making it the direct answer to what non-shivering thermogenesis is "due to." *Noradrenaline* - **Noradrenaline** is the key neurotransmitter that **activates brown fat** via **β3-adrenergic receptors** to initiate non-shivering thermogenesis. - While noradrenaline is the **trigger/stimulus**, the actual heat production occurs in brown adipose tissue. - Noradrenaline itself does not produce heat directly; it acts as the signal that activates the thermogenic machinery in BAT. *Thyroid hormone* - **Thyroid hormone** increases **basal metabolic rate** and can potentiate the thermogenic response by upregulating UCP1 expression in brown fat. - Its role is **permissive and long-term** rather than being the immediate effector of acute non-shivering thermogenesis. - It modulates overall cellular metabolism but is not the primary mechanism for rapid heat generation in cold exposure. *Muscle metabolism* - **Muscle contraction** during shivering generates heat through increased ATP hydrolysis, which is **shivering thermogenesis**. - **Non-shivering thermogenesis** specifically refers to heat production **without muscle contraction**, making muscle metabolism the mechanism for shivering, not non-shivering, thermogenesis.

Q: Prostaglandins (PGs) in semen are secreted by?

Seminal vesicle. ***Seminal vesicle*** - The **seminal vesicles** are the primary source of **prostaglandins (PGs)** in semen, contributing significantly to the seminal fluid volume. - These PGs play a crucial role in promoting **sperm motility** and facilitating fertilization. *Prostate* - The **prostate gland** primarily secretes **citrate**, **acid phosphatase**, and **prostate-specific antigen (PSA)**, which contribute to sperm activation and semen liquefaction. - It does not significantly contribute to the prostaglandin content of semen. *Sperms* - **Spermatozoa** themselves primarily contribute genetic material and are not a significant source of prostaglandin synthesis in semen. - Their main function is fertilization, not the production of accessory gland secretions. *Testes* - The **testes** are responsible for **spermatogenesis** (sperm production) and the synthesis of **androgens** like testosterone. - They do not secrete prostaglandins into the seminal fluid.

Question 1

Which of the following cell types is neuroectodermal in origin?

Accepted Answer

Smooth muscle cells

Answer

Skeletal muscle cells

Answer

Endothelial cells

Answer

Cardiac muscle cells

Question 2

Where does oxidative deamination primarily occur in the human body?

Accepted Answer

Mitochondria of liver cells

Answer

Cytoplasm of all cells

Answer

Mitochondria of all cells

Answer

Cytoplasm of liver cells

Question 3

Which of the following statements BEST describes the net ATP production in glycolysis?

Accepted Answer

Glycolysis produces a net gain of 2 ATP per glucose molecule

Answer

Glycolysis produces 2 molecules of pyruvate

Answer

Hexokinase consumes ATP during glycolysis

Answer

Aldolase catalyzes the conversion of fructose-1,6-bisphosphate into two three-carbon molecules

Question 4

Which of the following substances does not inhibit glycolysis?

Accepted Answer

Fluoroacetate

Answer

Fluoride

Answer

Arsenite

Answer

Iodoacetate

Question 5

Which tissue cannot convert glucose 6-phosphate to free glucose due to lack of glucose-6-phosphatase?

Accepted Answer

Muscle

Answer

Liver

Answer

Kidney

Answer

Adipose tissue

Question 6

At which positions does pancreatic lipase hydrolyze the ester linkages of triacylglycerides?

Accepted Answer

1 and 3

Answer

1 and 2

Answer

2 and 3

Answer

Only 3

Question 7

Which type of fatty acids should be included in the diet to manage chyluria?

Accepted Answer

Medium-chain fatty acids

Answer

Short-chain fatty acids

Answer

Long-chain fatty acids

Answer

Omega-3 fatty acids

Question 8

What color is emitted by FITC after absorbing blue light?

Accepted Answer

Yellow-green

Answer

Orange-red

Answer

Apple-green

Answer

Golden-brown

Question 9

Nonshivering thermogenesis in adults is due to:

Accepted Answer

Brown fat between the shoulders

Answer

Muscle metabolism

Answer

Thyroid hormone

Answer

Noradrenaline

Question 10

Prostaglandins (PGs) in semen are secreted by?

Accepted Answer

Seminal vesicle

Answer

Prostate

Answer

Sperms

Answer

Testes

NEET-PG 2012

Anatomy

Biochemistry

Internal Medicine

Pathology

Physiology