NEET-PG 2017 Practice Questions

Q: Which of the following is correct about the image shown below?

A = Sphenoid sinus, B= Auditory tube opening. ***A = Sphenoid sinus, B= Auditory tube opening*** - Label **A** clearly points to the **sphenoid sinus**, an air-filled cavity within the sphenoid bone, located posterior to the nasal cavity and inferior to the sella turcica. - Label **B** indicates the opening of the **auditory (Eustachian) tube** in the lateral wall of the nasopharynx, connecting the nasopharynx to the middle ear. *A = Cisterna magna, B= Posterior nasal aperture* - **Cisterna magna** is a subarachnoid space located posterior to the cerebellum and medulla, not visible at this anterior anatomical location. - The **posterior nasal aperture (choana)** is the opening between the nasal cavity and the nasopharynx, which is located more anteriorly and inferiorly relative to point B. *A = Ethmoidal sinus, B= Auditory tube opening* - The **ethmoidal sinuses** are located anterior to the sphenoid sinus, within the ethmoid bone, and would appear more superior and anterior to where A is located. - While B is correctly identified as the auditory tube opening, A is misplaced for the ethmoidal sinus. *A = Sella turcica, B= Posterior nasal aperture* - The **sella turcica** is a saddle-shaped depression in the sphenoid bone, superior to the sphenoid sinus, which houses the pituitary gland. - The **posterior nasal aperture** is incorrect for B, as explained above.

Q: Identify the structure marked as X in the specimen of left cubital fossa

Brachial artery. ***Brachial artery*** - The structure marked X is a prominent, thick-walled vessel consistent with the **brachial artery**, which passes through the cubital fossa. - The brachial artery is typically found medial to the **biceps brachii tendon** and lateral to the **median nerve** in the cubital fossa. *Biceps brachii* - The **biceps brachii** is a muscle, and while its tendon passes through the cubital fossa, the structure marked X is clearly a vessel, not a muscle or tendon. - The biceps brachii muscle is usually much larger and fleshy, not a defined linear structure like X. *Radial recurrent artery* - The **radial recurrent artery** is a smaller branch arising from the radial artery, which subsequently branches off the brachial artery. - It is significantly smaller and less prominent than the structure marked X, which appears to be a main vessel. *Posterior interosseous nerve* - The **posterior interosseous nerve** is a branch of the radial nerve and is primarily a nerve structure, which appears white/yellowish and thinner than the structure marked X, which is a blood vessel. - It typically winds around the neck of the radius and passes into the posterior compartment of the forearm, not usually as prominently displayed within the cubital fossa in this manner.

Q: The following image of posterior abdominal wall and pelvic inlet shows a structure marked as X. Identify it:

Superior hypogastric plexus. ***Superior hypogastric plexus*** - The structure marked 'X' is a prominent plexus of nerves located anterior to the **aortic bifurcation** and sacral promontory, a characteristic position for the superior hypogastric plexus. - This plexus is involved in relaying **sympathetic innervation** to the pelvic viscera. *Ureter* - The ureter is a muscular tube that transports urine from the kidney to the bladder and is typically found running inferiorly and medially, often crossing the **common iliac vessels**. - Its appearance would be more tubular and less spread out than the depicted neural plexus. *Obturator nerve* - The obturator nerve arises from the **lumbar plexus** (L2-L4) and descends through the psoas major muscle, typically entering the lesser pelvis to supply the medial thigh compartment. - It would appear as a distinct nerve, not a broad plexus, and is usually found more laterally relative to **midline structures** in this view. *Genitofemoral nerve* - The genitofemoral nerve (L1, L2) pierces the **psoas major muscle** and soon splits into genital and femoral branches, running on the surface of the psoas. - Its slender, linear appearance and more lateral course differentiate it from the structure shown, which is a broader nerve network.

Q: A patient reports a change in colour of urine on air exposure. All are true about the condition shown below except:

Urine Benedict's test is negative. ***Urine Benedict's test is negative*** - This is FALSE - Benedict's test is actually **POSITIVE** in alkaptonuria because **homogentisic acid** is a reducing agent. - Homogentisic acid readily **reduces Benedict's reagent**, giving a positive test result in alkaptonuria patients. *Blackening of urine is accelerated on exposure to sunlight* - This is TRUE - **UV light** and sunlight accelerate the **oxidation of homogentisic acid** in urine. - The characteristic **dark discoloration** occurs more rapidly when exposed to light and air. *Alkaptone bodies are deposited in intervertebral disc* - This is TRUE - **Homogentisic acid (alkaptone bodies)** polymerizes to form **ochronotic pigment** deposits. - These deposits accumulate in **cartilage** including intervertebral discs, causing degenerative changes and spondylosis. *The condition is caused by deficiency of homogentisate 1,2-dioxygenase* - This is TRUE - Alkaptonuria is caused by deficiency of **homogentisate 1,2-dioxygenase** enzyme in the **tyrosine metabolic pathway**. - This enzyme deficiency leads to accumulation of **homogentisic acid** in blood and urine, causing the characteristic symptoms.

Q: Name the product marked as X in the image shown below:

Indolequinone. ***Indolequinone*** - The image depicts the **melanin biosynthesis pathway** starting from **tyrosine**. - Tyrosine is converted to **L-DOPA** by tyrosinase, which is then oxidized to **dopaquinone** (also called DOPA-quinone). - Dopaquinone undergoes intramolecular cyclization to form **leucodopachrome**, which is subsequently oxidized to **dopachrome**. - Dopachrome is then converted through a series of steps to **5,6-dihydroxyindole**, which is finally oxidized to **indole-5,6-quinone** (indolequinone). - **Indolequinone** is a key intermediate that polymerizes to form **melanin**, the pigment responsible for coloration in skin, hair, and eyes. - Based on the pathway shown, X represents indolequinone, an oxidized indole derivative in melanin synthesis. *Tetrabenazine* - **Tetrabenazine** is a pharmaceutical drug that inhibits **vesicular monoamine transporter 2 (VMAT2)**. - It is used therapeutically to treat hyperkinetic movement disorders such as **Huntington's disease** and tardive dyskinesia. - It is not a natural metabolic intermediate in the tyrosine-to-melanin biosynthetic pathway. *Homovanillic acid* - **Homovanillic acid (HVA)** is a major end metabolite of **dopamine** in the catecholamine degradation pathway. - It is formed by the sequential actions of **monoamine oxidase (MAO)** and **catechol-O-methyltransferase (COMT)** on dopamine. - This represents a completely different branch of tyrosine metabolism (catecholamine pathway), not the melanin synthesis pathway. *Kynurenine* - **Kynurenine** is an intermediate metabolite in the **kynurenine pathway**, which is the major route of **tryptophan** degradation. - The kynurenine pathway leads to the formation of NAD+ and various neuroactive metabolites. - This pathway is completely separate from tyrosine metabolism and is unrelated to the melanin synthesis pathway shown in the image.

Q: All are correct about the amino acid marked as X, EXCEPT:

Ketogenic. ***Correct Answer: Ketogenic*** ✓ - Histidine is **purely glucogenic**, NOT ketogenic - Its carbon skeleton is converted to α-ketoglutarate (a TCA cycle intermediate), which can be used for gluconeogenesis - It does NOT produce acetyl-CoA or acetoacetate (ketone body precursors) - **This statement is FALSE, making it the correct answer for this EXCEPT question** *Incorrect: Maximum buffering action* - This statement is TRUE (so not the answer) - Histidine contains an **imidazole ring** with pKa ~6.0, close to physiological pH - Provides crucial **buffering capacity** in blood and tissues - Most effective amino acid buffer at physiological pH *Incorrect: Contributes to one carbon pool* - This statement is TRUE (so not the answer) - Histidine breakdown produces **Formimino glutamic acid (FIGLU)** - FIGLU donates its formimino group to **Tetrahydrofolate (THF)** - Contributes to the **one-carbon pool** essential for biosynthetic pathways *Incorrect: Excess amount leads to mental retardation* - This statement is TRUE (so not the answer) - **Histidinemia** results from histidase enzyme deficiency - Elevated histidine levels can be associated with **developmental delays and speech defects** in some cases - Though many affected individuals remain asymptomatic

Q: Name the plot dealing with kinetics of enzyme inhibition?

Dixon plot. ***Dixon plot*** - The **Dixon plot** is specifically used to determine the type of enzyme inhibition and to calculate the **inhibition constant (Ki)**. - It plots the reciprocal reaction velocity (1/V) against the **inhibitor concentration ([I])** at different substrate concentrations. *Donnan-Gibbs equation plot* - The **Donnan-Gibbs equation** describes the distribution of charged particles across a semi-permeable membrane at equilibrium. - It is irrelevant to enzyme kinetics or inhibition. *Lineweaver-Burk plot* - While the Lineweaver-Burk plot is used in enzyme kinetics to determine **Km** and **Vmax** and analyze inhibition, it plots **1/V against 1/[S]**. - The image provided, showing 1/V against [I], is characteristic of a Dixon plot, not a Lineweaver-Burk plot which plots 1/V against 1/[S]. *Hanes-Woolf plot* - The **Hanes-Woolf plot** is another linearization of the Michaelis-Menten equation, plotting **[S]/V against [S]**. - Like the Lineweaver-Burk plot, it is used for analyzing general enzyme kinetics but not specifically for determining Ki from varying inhibitor concentrations in the manner shown.

Q: Which enzyme marked as $X$ is missing in synthesis of vitamin $D_{3}$ ?

17-alpha-hydroxylase. ***17-alpha-hydroxylase*** - The diagram illustrates the synthesis of **vitamin D3**, which involves hydroxylation steps at positions C-25 in the liver and C-1 in the kidneys. These are catalyzed by **25-hydroxylase** and **1-alpha-hydroxylase**, respectively. - **17-alpha-hydroxylase** is involved in the synthesis of steroid hormones (like cortisol, androgens, and estrogens) from cholesterol, not in the synthesis or metabolism of vitamin D3; therefore, its absence would not be relevant to vitamin D synthesis. *3-beta-hydroxylase* - **3-beta-hydroxysteroid dehydrogenase** is crucial for the synthesis of all steroid hormones, converting delta-5-3-hydroxysteroids to delta-4-3-ketosteroids. - Its presence is essential for **steroidogenesis**, but it does not play a direct role in the specific hydroxylation steps for vitamin D activation. *21-hydroxylase* - **21-hydroxylase** is an enzyme involved in the synthesis of steroid hormones such as cortisol and aldosterone from progesterone and 17-hydroxyprogesterone. - Deficiency of this enzyme leads to **congenital adrenal hyperplasia**, a condition unrelated to vitamin D metabolism. *24-hydroxylase* - **24-hydroxylase** is responsible for the inactivation of vitamin D metabolites by adding a hydroxyl group at position C-24, leading to degradation. - This enzyme is part of the **catabolic pathway** to regulate vitamin D levels, rather than being a missing enzyme in the primary synthesis of active vitamin D.

Q: The following reaction occurs in which part of kidney?

Proximal convoluted tubule. **Proximal convoluted tubule** - The image shows the conversion of 25-hydroxycholecalciferol to **1,25 (OH)₂-D₃**, also known as calcitriol, via the enzyme **1α-hydroxylase**. - This critical hydroxylation reaction, occurring primarily in the **proximal convoluted tubule** cells of the kidney, produces the biologically active form of vitamin D. *Distal convoluted tubule* - The distal convoluted tubule is primarily involved in **fine-tuning** water and electrolyte reabsorption, influenced by hormones like aldosterone and antidiuretic hormone. - It does not contain the necessary enzymes, specifically **1α-hydroxylase**, for the final activation step of vitamin D. *Loop of Henle* - The loop of Henle's main function is to create a **medullary osmotic gradient** through countercurrent multiplication, crucial for concentrating urine. - It plays no significant role in the **hydroxylation of vitamin D** precursors. *Collecting duct* - The collecting duct is responsible for final adjustments to urine volume and concentration, largely under the influence of **antidiuretic hormone**. - It lacks the **enzymatic machinery** (1α-hydroxylase) required for the activation of vitamin D.

Question 1

Which of the following is correct about the image shown below?

Accepted Answer

A = Sphenoid sinus, B= Auditory tube opening

Answer

A = Cisterna magna, B= Posterior nasal aperture

Answer

A = Ethmoidal sinus, B= Auditory tube opening

Answer

A = Sella turcica, B= Posterior nasal aperture

Question 2

Identify the structure marked as X in the specimen of left cubital fossa

Accepted Answer

Brachial artery

Answer

Biceps brachii

Answer

Radial recurrent artery

Answer

Posterior interosseous nerve

Question 3

The following image of posterior abdominal wall and pelvic inlet shows a structure marked as X. Identify it:

Accepted Answer

Superior hypogastric plexus

Answer

Ureter

Answer

Obturator nerve

Answer

Genitofemoral nerve

Question 4

Which is correct about the markings shown on the left popliteal fossa? (Recent NEET Pattern 2016-17)

Accepted Answer

1 = Popliteal artery, 2= popliteal vein, 3= tibial nerve, 4= Semimembranosus

Answer

1 = Tibial nerve, 2= popliteal vein, 3= popliteal artery, 4= Semitendinosus

Answer

1 = Popliteal artery, 2= popliteal vein, 3= tibial nerve, 4= Semitendinosus

Answer

1 = Tibial nerve, 2= popliteal vein, 3= popliteal artery, 4= Semimembranosus

Question 5

A patient reports a change in colour of urine on air exposure. All are true about the condition shown below except:

Accepted Answer

Urine Benedict's test is negative

Answer

Blackening of urine is accelerated on exposure to sunlight

Answer

Alkaptone bodies are deposited in intervertebral disc

Answer

The condition is caused by deficiency of homogentisate 1,2-dioxygenase

Question 6

Name the product marked as X in the image shown below:

Accepted Answer

Indolequinone

Answer

Tetrabenazine

Answer

Homovanillic acid

Answer

Kynurenine

Question 7

All are correct about the amino acid marked as X, EXCEPT:

Accepted Answer

Ketogenic

Answer

Maximum buffering action

Answer

Contributes to one carbon pool

Answer

Excess amount leads to mental retardation

Question 8

Name the plot dealing with kinetics of enzyme inhibition?

Accepted Answer

Dixon plot

Answer

Donnan-Gibbs equation plot

Answer

Lineweaver-Burk plot

Answer

Hanes-Woolf plot

Question 9

Which enzyme marked as $X$ is missing in synthesis of vitamin $D_{3}$ ?

Accepted Answer

17-alpha-hydroxylase

Answer

3-beta-hydroxylase

Answer

21-hydroxylase

Answer

24-hydroxylase

Question 10

The following reaction occurs in which part of kidney?

Accepted Answer

Proximal convoluted tubule

Answer

Distal convoluted tubule

Answer

Loop of Henle

Answer

Collecting duct

NEET-PG 2017

Anatomy

Biochemistry