NEET-PG 2012 Practice Questions

Q: Which of the following statements about the Corpus Callosum is correct?

Connects the left and right hemispheres. ***Connects the left and right hemispheres*** - The **corpus callosum** is the largest **commissural white matter tract** in the brain, uniquely designed to facilitate communication between the **corresponding regions** of the left and right cerebral hemispheres [1]. - Its primary function is to integrate **sensory, motor, and cognitive information** processed in each hemisphere, ensuring coordinated brain activity [1]. *Connects distant areas of the two sides of the brain* - While it connects regions on the two sides of the brain, the statement is too broad and does not specify its role in connecting **corresponding** or **homologous** areas across the hemispheres. - Other fiber tracts (e.g., **anterior commissure**) also connect different areas between the two sides, but the corpus callosum is specific to the **cerebral hemispheres**. *Connects the two frontal lobes* - The corpus callosum connects all four lobes (frontal, parietal, temporal, occipital) between the two hemispheres, not exclusively the **frontal lobes**. - While it does contain fibers connecting the frontal lobes, this statement is **incomplete** and does not capture its overall function. *All of the options* - Since the other options are either **incorrect** or **incomplete**, this option cannot be correct. - The most accurate and encompassing description of the corpus callosum's function among the choices is connecting the left and right hemispheres.

Q: The thyrocervical trunk is a branch of which part of subclavian artery?

1st part. ***1st part*** - The **thyrocervical trunk** is one of the three primary branches arising from the **first part** of the subclavian artery. - The first part lies medial to the **anterior scalene muscle**. *2nd part* - The **second part** of the subclavian artery gives rise to the **costocervical trunk**. - This part lies posterior to the **anterior scalene muscle**. *3rd part* - The **third part** of the subclavian artery typically has no branches or may give off the **dorsal scapular artery**. - This part lies lateral to the **anterior scalene muscle**. *4th part* - This option is incorrect as the **subclavian artery has only three parts**, divided by their relationship to the anterior scalene muscle. - There is no anatomical fourth part of the subclavian artery.

Q: Which of the following is NOT an anterior relation of the right kidney?

4th part of duodenum. ***4th part of duodenum*** - The **4th part of the duodenum** is located to the **left of the vertebral column** and is related to the **left kidney**, not the right kidney. - This segment passes superiorly along the left side of the aorta to become continuous with the jejunum at the duodenojejunal flexure. *Liver* - The **right kidney's superior part** is in direct contact with the **right lobe of the liver**, often separated only by the peritoneum [1]. - This is a significant anterior relation, explaining why liver enlargement can sometimes displace the right kidney. *Hepatic flexure* - The **hepatic flexure** (right colic flexure) of the colon lies immediately inferior to the liver and anterior to the **lower part of the right kidney**. - This anatomical relationship means that the right kidney can be affected by diseases of the colon in this region. *2nd part of duodenum* - The **descending (2nd) part of the duodenum** lies anterior to the **hilum and medial part of the right kidney** [1]. - Its retroperitoneal position places it in close proximity to the renal structures, making it a key anterior relation.

Q: Acute intermittent porphyria is due to deficiency of?

Porphobilinogen deaminase. ***Porphobilinogen deaminase*** - **Acute intermittent porphyria (AIP)** results from a deficiency in **porphobilinogen deaminase** (also known as hydroxymethylbilane synthase). - This enzyme deficiency leads to the accumulation of **aminolevulinic acid (ALA)** and **porphobilinogen (PBG)**, which are neurotoxic and cause the characteristic symptoms of AIP. *Uroporphyrinogen III synthase* - A deficiency in **uroporphyrinogen III synthase** causes **congenital erythropoietic porphyria (Günther disease)**, which is characterized by severe photosensitivity and hemolytic anemia. - This enzyme defect leads to the accumulation of uroporphyrinogen I and coproporphyrinogen I, not the ALA and PBG associated with AIP. *Ferrochelatase* - Deficiency in **ferrochelatase** causes **erythropoietic protoporphyria (EPP)**, which presents with photosensitivity and chronic liver disease due to the accumulation of **protoporphyrin**. - This condition does not cause the acute neurological attacks seen in AIP. *ALA synthase* - **ALA synthase** is the **rate-limiting enzyme** in heme synthesis; while its activity is crucial, a congenital *deficiency* is not the cause of AIP. - Instead, the *upregulation* of ALA synthase activity in AIP (due to the PBG deaminase block) contributes to the accumulation of ALA and PBG.

Q: Km value is defined as:

Substrate concentration at Vmax/2. ***Substrate concentration at Vmax/2*** - The **Michaelis constant (Km)** is defined as the **substrate concentration** at which the reaction velocity is **half of the maximum velocity (Vmax/2)**. - It reflects the **affinity of an enzyme for its substrate**; a lower Km indicates higher affinity. *Substrate concentration at which reaction rate is maximum* - The **maximum reaction rate (Vmax)** is achieved when the enzyme is **saturated with substrate**, meaning all active sites are occupied. - Km specifically refers to the substrate concentration needed to reach **half of this maximum rate**, not the maximum rate itself. *Substrate concentration at Vmax* - At **Vmax**, the enzyme is fully saturated with substrate, and the reaction rate cannot increase further by adding more substrate. - The **Km value** is a measure related to the **efficiency of substrate binding** at conditions below saturation, specifically at half Vmax. *Substrate concentration at which enzyme activity is optimal* - **Optimal enzyme activity** is generally influenced by factors such as **pH and temperature**, which affect the enzyme's structure and catalytic efficiency. - Km is specifically related to the **substrate concentration** required to achieve a specific reaction rate, not the overall optimal environmental conditions for the enzyme.

Q: Which enzyme catalyzes the rate limiting step in the TCA cycle?

α-ketoglutarate dehydrogenase. **α-ketoglutarate dehydrogenase** - The **α-ketoglutarate dehydrogenase complex** catalyzes the oxidative decarboxylation of α-ketoglutarate to succinyl-CoA, producing NADH and CO2. - This step is a **major control point** in the TCA cycle and is highly regulated by: - **Product inhibition**: Succinyl-CoA and NADH - **Calcium ions**: Activate the enzyme - Along with isocitrate dehydrogenase and citrate synthase, it represents one of the three key regulatory enzymes of the TCA cycle. *Fumarase* - **Fumarase** catalyzes the reversible hydration of fumarate to L-malate. - This enzyme is **not a regulatory step** in the TCA cycle; its activity is typically high and not a control point for the overall flux of the cycle. *Aconitase* - **Aconitase** catalyzes the reversible isomerization of citrate to isocitrate, via the intermediate cis-aconitate. - While important for the cycle's progression, aconitase activity is **not considered a rate-limiting step** for the overall regulation of the TCA cycle. *Thiokinase* - The term **thiokinase** (or succinyl-CoA synthetase) catalyzes the reversible conversion of succinyl-CoA to succinate, coupled with GTP/ATP production. - This enzyme is responsible for **substrate-level phosphorylation** in the TCA cycle but does not represent a primary regulatory or rate-limiting step.

Q: Pantothenic acid is needed for donating the following moiety?

Acetyl group. ***Acetyl group*** - **Pantothenic acid** (vitamin B5) is a crucial component of **coenzyme A (CoA)**, which plays a central role in transferring **acetyl groups**. - This transfer is vital in numerous metabolic pathways, including the **Krebs cycle**, fatty acid synthesis, and fatty acid oxidation. *Carboxyl* - The transfer of **carboxyl groups** is typically mediated by a different coenzyme, **biotin** (vitamin B7), not pantothenic acid. - Biotin-dependent enzymes are involved in carboxylation reactions like those in gluconeogenesis and fatty acid synthesis. *Hydroxyl* - While hydroxyl groups are common in organic chemistry, pantothenic acid's primary role is not the donation of isolated **hydroxyl groups**. - Hydroxyl groups are often donated or accepted during redox reactions or hydrolysis, often by specific enzymes directly. *Amino* - The transfer of **amino groups** is primarily associated with **pyridoxal phosphate (PLP)**, the active form of vitamin B6. - PLP-dependent enzymes, such as **transaminases**, are critical for amino acid metabolism.

Q: What is the venous hematocrit level at which you will diagnose polycythemia in a newborn?

65%. ***Correct: 65%*** - **Polycythemia** in a newborn is typically diagnosed when the **venous hematocrit** is **≥65%**. - This threshold indicates an abnormally high concentration of **red blood cells**, increasing blood viscosity. *Incorrect: 55%* - A venous hematocrit of 55% is generally considered within the **normal range** for a newborn, especially within the first few hours of life. - It does not meet the criteria for diagnosing **polycythemia**. *Incorrect: 60%* - While 60% is elevated compared to adult norms, it is still generally within the higher end of the **normal range** for an infant. - This level alone is usually **not sufficient** to diagnose **polycythemia** or warrant intervention without other clinical signs. *Incorrect: 70%* - A venous hematocrit of 70% definitely indicates **polycythemia** and significant **hyperviscosity**. - However, the diagnostic threshold for polycythemia is **65%**, meaning the condition is identified earlier.

Q: Peripheral and central chemoreceptors may both contribute to the increased ventilation that occurs as a result of which of the following?

An increase in arterial carbon dioxide tension. ***An increase in arterial carbon dioxide tension*** - An increase in **arterial PCO2** (hypercapnia) leads to a rapid decrease in the **pH of the cerebrospinal fluid (CSF)**, which strongly stimulates **central chemoreceptors** in the medulla. - While overwhelmingly driven by central chemoreceptors, a significant increase in **arterial PCO2** also causes a slight decrease in **arterial pH**, which can additionally stimulate **peripheral chemoreceptors** in the carotid and aortic bodies, leading to increased ventilation. *A decrease in arterial oxygen content* - A decrease in **arterial oxygen content** (e.g., due to anemia or carbon monoxide poisoning) without a significant drop in **arterial PO2** primarily affects oxygen delivery to tissues. - It does not directly stimulate peripheral chemoreceptors, which are sensitive to **PO2**, not content, nor does it affect central chemoreceptors directly to increase ventilation in this manner. *A decrease in arterial blood pressure* - A decrease in **arterial blood pressure** is sensed by **baroreceptors** and primarily triggers cardiovascular reflexes (e.g., increased heart rate and vasoconstriction) to restore blood pressure. - It does not directly stimulate peripheral or central chemoreceptors to significantly increase ventilation unless severe hypoperfusion leads to significant changes in arterial blood gases. *A decrease in arterial oxygen tension* - A decrease in **arterial oxygen tension (PO2)**, especially when it falls below approximately 60 mmHg, acts as a potent stimulus for **peripheral chemoreceptors**. - However, **central chemoreceptors** are primarily sensitive to **PCO2** and CSF pH, and a decrease in **arterial PO2** alone has little direct effect on their activity.

Question 1

Which statement accurately describes a characteristic of synovial joints?

Accepted Answer

Hyaline cartilage covers the articular surfaces of synovial joints.

Answer

The metacarpo-phalangeal joint is a condyloid joint.

Answer

Cartilage can sometimes divide the joint into two cavities.

Answer

Stability is inversely proportional to mobility in synovial joints.

Question 2

Which of the following statements about the Corpus Callosum is correct?

Accepted Answer

Connects the left and right hemispheres

Answer

All of the options

Answer

Connects distant areas of the two sides of the brain

Answer

Connects the two frontal lobes

Question 3

The thyrocervical trunk is a branch of which part of subclavian artery?

Accepted Answer

1st part

Answer

2nd part

Answer

3rd part

Answer

4th part

Question 4

Which of the following is NOT an anterior relation of the right kidney?

Accepted Answer

4th part of duodenum

Answer

Hepatic flexure

Answer

Liver

Answer

2nd part of duodenum

Question 5

Acute intermittent porphyria is due to deficiency of?

Accepted Answer

Porphobilinogen deaminase

Answer

Uroporphyrinogen III synthase

Answer

Ferrochelatase

Answer

ALA synthase

Question 6

Km value is defined as:

Accepted Answer

Substrate concentration at Vmax/2

Answer

Substrate concentration at which reaction rate is maximum

Answer

Substrate concentration at Vmax

Answer

Substrate concentration at which enzyme activity is optimal

Question 7

Which enzyme catalyzes the rate limiting step in the TCA cycle?

Accepted Answer

α-ketoglutarate dehydrogenase

Answer

Fumarase

Answer

Aconitase

Answer

Thiokinase

Question 8

Pantothenic acid is needed for donating the following moiety?

Accepted Answer

Acetyl group

Answer

Carboxyl

Answer

Hydroxyl

Answer

Amino

Question 9

What is the venous hematocrit level at which you will diagnose polycythemia in a newborn?

Accepted Answer

65%

Answer

55%

Answer

60%

Answer

70%

Question 10

Peripheral and central chemoreceptors may both contribute to the increased ventilation that occurs as a result of which of the following?

Accepted Answer

An increase in arterial carbon dioxide tension

Answer

A decrease in arterial oxygen content

Answer

A decrease in arterial blood pressure

Answer

A decrease in arterial oxygen tension

NEET-PG 2012

Anatomy

Biochemistry

Pediatrics

Physiology