NEET-PG 2013 Practice Questions

Q: Which chamber of the heart forms the posterior surface?

Left Atrium (LA). ***Left Atrium (LA)*** - The **left atrium** forms the posterior surface of the heart, lying in front of the esophagus and thoracic aorta [1]. - Its posterior position makes it susceptible to enlargement, which can compress the **esophagus** and cause dysphagia [1]. *Right Atrium (RA)* - The **right atrium** primarily forms the right border of the heart and receives deoxygenated blood from the systemic circulation. - It lies anteriorly and to the right, behind the sternum and costal cartilages. *Left Ventricle (LV)* - The **left ventricle** forms the apex of the heart and part of the left border. - It is positioned *inferiorly* and *anteriorly*, contributing significantly to the *diaphragmatic surface* of the heart. *Right Ventricle (RV)* - The **right ventricle** forms the majority of the anterior surface of the heart, directly behind the sternum. - It also contributes to the *inferior surface* of the heart, resting on the diaphragm.

Q: Vertebral arteries of both sides unite to form

Basilar artery. Basilar artery - The paired vertebral arteries ascend through the neck via the transverse foramina of cervical vertebrae and enter the skull through the foramen magnum. - At the level of the pontomedullary junction, the two vertebral arteries merge to form a single basilar artery. Anterior spinal artery - The anterior spinal artery is formed by the union of two small branches derived from each vertebral artery near their intracranial origin. - It supplies the anterior two-thirds of the spinal cord, running along the anterior median fissure. Posterior spinal artery - The posterior spinal arteries are typically two vessels, one arising from each vertebral artery (or less commonly from the posterior inferior cerebellar artery). - They supply the posterior one-third of the spinal cord and do not form a single major merged vessel in the brainstem. Medullary artery - There is no single major artery termed the "medullary artery" formed by the union of the vertebral arteries. - The medulla oblongata is supplied by branches directly from the vertebral arteries and the basilar artery, such as the posterior inferior cerebellar artery (PICA) and direct medullary branches.

Q: What is the nerve supply to the muscles of the flexor compartment of the arm?

Musculocutaneous nerve. ***Musculocutaneous nerve*** - The **musculocutaneous nerve** is the primary nerve supplying all three muscles in the **flexor compartment of the arm**: the **biceps brachii**, **brachialis**, and **coracobrachialis**. - Its motor branches innervate these muscles, allowing for **flexion at the elbow** and **supination of the forearm**. *Median nerve* - The **median nerve** primarily innervates most muscles in the **flexor compartment of the forearm**, not the arm. - It plays a crucial role in **wrist and finger flexion**, as well as movements of the **thenar eminence**. *Radial nerve* - The **radial nerve** is the main nerve for the **extensor compartment of the arm and forearm**. - It is responsible for **elbow, wrist, and finger extension**. *Ulnar nerve* - The **ulnar nerve** primarily supplies intrinsic muscles of the hand and some flexor muscles in the forearm. - It has no motor supply to the muscles of the **flexor compartment of the arm**.

Q: Which muscle plays a role in winking?

Orbicularis oculi. ***Orbicularis oculi*** - This muscle is responsible for **closing the eyelid** and is essential for actions like blinking, squinting, and winking. - Its fibers encircle the eye and facilitate the **controlled closure** required for winking. *Levator labii superioris* - This muscle primarily functions to **elevate the upper lip**, playing a role in facial expressions such as sneering or smiling. - It has no direct involvement in the movement of the eyelids or the act of winking. *Corrugator supercilii* - This muscle is located in the eyebrow region and is responsible for **drawing the eyebrows medially and inferiorly**, creating vertical wrinkles between the eyebrows. - It is associated with expressions of frowning or concern, not eyelid closure. *Levator palpebrae* - This muscle is responsible for **opening the upper eyelid**, thus counteracting the action of the orbicularis oculi. - While essential for eye movement, it is not involved in the closing action required for winking.

Q: Glucagon stimulates

Gluconeogenesis. ***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.

Q: Which enzyme polymerises Okazaki fragments?

DNA polymerase III. ***DNA polymerase III*** - **DNA polymerase III** is the primary replicative enzyme in **prokaryotes (bacteria)** responsible for synthesizing new DNA strands, including the **polymerization of Okazaki fragments** on the lagging strand. - It possesses high processivity (can add ~500 nucleotides without dissociating), essential for rapid and efficient DNA synthesis during replication, adding nucleotides in a **5' to 3' direction**. - In **eukaryotes**, DNA polymerase δ (delta) performs the analogous function of polymerizing Okazaki fragments. *DNA polymerase I* - **DNA polymerase I** in prokaryotes primarily functions in **removing RNA primers** left by primase and **filling the resulting gaps** with DNA nucleotides. - It has 5' to 3' exonuclease activity for primer removal and polymerase activity for gap filling, but is **not the main enzyme for elongating Okazaki fragments**. - Its role is in **DNA repair and finishing replication**, not the extensive synthesis of Okazaki fragments. *DNA polymerase II* - **DNA polymerase II** in prokaryotes is primarily involved in **DNA repair mechanisms**, particularly in **restarting stalled replication forks** and responding to DNA damage. - It is not the main enzyme responsible for the polymerization of **Okazaki fragments** during normal DNA replication. *RNA polymerase* - **RNA polymerase** (specifically **primase**, a specialized RNA polymerase) synthesizes short **RNA primers** (8-12 nucleotides) during DNA replication, which provide the 3'-OH group necessary to initiate DNA synthesis. - It does not synthesize DNA or polymerize **Okazaki fragments**; its function is to create RNA primers, not extend DNA strands.

Q: What is the typical Q10 value for enzymatic reactions?

2. ***2*** - The **Q10 value** represents the factor by which the rate of a reaction increases for every 10°C rise in temperature. - For most enzymatic and biological reactions, the **Q10 value** is typically around **2 to 3**. *3* - While **3** is within the typical range for some biological reactions, **2** is often considered the most common or average value cited for enzymatic reactions. - A **Q10 of 3** means the reaction rate triples with a 10°C increase, which is observed in certain cases but is not the most general "typical" value. *4* - A **Q10 value of 4** indicates a significantly higher temperature sensitivity than what is commonly observed for most enzymatic reactions. - Such a high Q10 would imply that the reaction rate quadruples for every 10°C increase, which is less typical. *5* - A **Q10 value of 5** is exceptionally high and rarely observed for common enzymatic reactions under physiological conditions. - This would suggest an extreme sensitivity to temperature changes, which is not characteristic of most enzyme kinetics.

Q: What is the main enzyme involved in glycogen breakdown (glycogenolysis)?

Glycogen phosphorylase. ***Glycogen phosphorylase*** - This is the **rate-limiting and primary enzyme** for **glycogenolysis**, the breakdown of glycogen into glucose units. - It cleaves **α-1,4-glycosidic bonds** in glycogen, releasing **glucose-1-phosphate** units. - Regulated by both **allosteric mechanisms** and **hormonal control** (epinephrine, glucagon). - Works until it reaches 4 glucose residues from a branch point, where debranching enzyme takes over. *Glycogen synthase* - This is the main enzyme for **glycogenesis** (glycogen synthesis), not breakdown. - It catalyzes formation of α-1,4-glycosidic bonds to build glycogen chains. - This is the opposite direction of metabolism from what the question asks about. *Glucose-6-phosphatase* - This enzyme is involved in **gluconeogenesis** and the final step of converting **glucose-6-phosphate to free glucose**. - It is NOT directly involved in glycogen breakdown itself, but rather in the subsequent conversion pathway. - Found primarily in **liver and kidney** to release free glucose into blood. *Hexokinase* - This enzyme phosphorylates free glucose to **glucose-6-phosphate** (opposite direction). - It is involved in **glucose utilization**, not glycogen breakdown. - It traps glucose inside cells for metabolism or glycogen synthesis.

Q: Which of the following statements about HIV associated nephropathy (HIVAN) is incorrect?

HIVAN is associated with shrunken kidneys.. ***Shrunken kidneys*** - In HIV-associated nephropathy, kidneys typically appear **enlarged** due to hyperplasia of podocytes and other glomerular changes. - **Shrunken kidneys** are not a characteristic feature, making this statement incorrect. *Develops when CD4<200* - HIV-associated nephropathy often arises when CD4 counts drop **below 200 cells/mm³**, indicating severe immunosuppression. - This is a common threshold for the occurrence of opportunistic infections and kidney issues in HIV patients. *15% cases show mesengial proliferation* - **Mesangial proliferation** can occur in about **15% to 30%** of cases of HIV-associated nephropathy, which aligns with the typical histological findings. - Incorrect assumptions might stem from misunderstanding the varying morphologies associated with HIV nephropathy. *Proteinuria* - **Proteinuria** is a common clinical feature of HIV-associated nephropathy, with the condition often presenting with significant protein loss in the urine. - The nephropathy especially results in **nephrotic syndrome**, characterized by high levels of proteinuria.

Q: What is the normal mean velocity of blood flow in the aorta?

40-50 cm/sec. ***40-50 cm/sec*** - This range represents the **normal mean velocity** of blood flow in the **aorta**, reflecting efficient cardiac output and systemic circulation. - Blood flow velocity can vary slightly based on factors like age, cardiac health, and physical activity, but this range is a common physiological benchmark. *100-150 cm/sec* - This velocity is significantly **higher** than normal for mean aortic flow and would typically indicate a state of **hyperdynamic circulation** or specific pathological conditions. - Such elevated velocities might be seen in conditions like severe **aortic stenosis**, where the heart works harder to push blood through a narrowed valve. *200-250 cm/sec* - This range is **pathologically high** for mean aortic blood flow and is not compatible with normal physiological function. - Velocities in this range would strongly suggest a severe **cardiovascular abnormality**, such as critical **aortic stenosis** or a significant **arteriovenous shunt**. *250-300 cm/sec* - This velocity is **extremely high** and far exceeds any normal or even most pathological mean aortic flow rates found in humans. - Such high velocities would likely be associated with a highly turbulent and severely compromised cardiovascular system, potentially leading to **acute circulatory failure**.

Question 1

Which chamber of the heart forms the posterior surface?

Accepted Answer

Left Atrium (LA)

Answer

Right Atrium (RA)

Answer

Left Ventricle (LV)

Answer

Right Ventricle (RV)

Question 2

Vertebral arteries of both sides unite to form

Accepted Answer

Basilar artery

Answer

Anterior spinal artery

Answer

Posterior spinal artery

Answer

Medullary artery

Question 3

What is the nerve supply to the muscles of the flexor compartment of the arm?

Accepted Answer

Musculocutaneous nerve

Answer

Median nerve

Answer

Radial nerve

Answer

Ulnar nerve

Question 4

Which muscle plays a role in winking?

Accepted Answer

Orbicularis oculi

Answer

Levator labii superioris

Answer

Levator palpebrae

Answer

Corrugator supercilii

Question 5

Glucagon stimulates

Accepted Answer

Gluconeogenesis

Answer

Glycogenesis

Answer

Fatty acid synthesis

Answer

Glycolysis

Question 6

Which enzyme polymerises Okazaki fragments?

Accepted Answer

DNA polymerase III

Answer

DNA polymerase I

Answer

DNA polymerase II

Answer

RNA polymerase

Question 7

What is the typical Q10 value for enzymatic reactions?

Accepted Answer

2

Answer

3

Answer

4

Answer

5

Question 8

What is the main enzyme involved in glycogen breakdown (glycogenolysis)?

Accepted Answer

Glycogen phosphorylase

Answer

Glycogen synthase

Answer

Glucose-6-phosphatase

Answer

Hexokinase

Question 9

Which of the following statements about HIV associated nephropathy (HIVAN) is incorrect?

Accepted Answer

HIVAN is associated with shrunken kidneys.

Answer

HIVAN is characterized by proteinuria.

Answer

HIVAN typically develops when CD4 count is less than 200.

Answer

About 15% of cases show mesangial proliferation.

Question 10

What is the normal mean velocity of blood flow in the aorta?

Accepted Answer

40-50 cm/sec

Answer

100-150 cm/sec

Answer

200-250 cm/sec

Answer

250-300 cm/sec

NEET-PG 2013

Anatomy

Biochemistry

Internal Medicine

Physiology