NEET-PG 2012 Practice Questions

Q: During incision and drainage of ischiorectal abscess, which nerve is most likely to be injured?

Inferior rectal nerve. ***Inferior rectal nerve*** - The **inferior rectal nerve** innervates the **external anal sphincter** and the skin around the anus, making it vulnerable during an incision and drainage of an **ischiorectal abscess** due to its anatomical proximity. - Injury to this nerve can lead to **fecal incontinence** or altered sensation in the perianal region. *Superior rectal nerve* - The **superior rectal nerve** is primarily involved in the innervation of the **rectum** and is not directly located in the area of an **ischiorectal abscess**. - This nerve supplies the smooth muscle of the rectum and is not anatomically vulnerable during incision and drainage of an abscess in the ischiorectal fossa. *Superior gluteal nerve* - The **superior gluteal nerve** supplies the **gluteus medius**, **gluteus minimus**, and **tensor fasciae latae muscles**, which are typically located much more superior and lateral to an **ischiorectal abscess**. - Damage to this nerve causes a characteristic **Trendelenburg gait**, which is unrelated to perianal surgery. *Inferior gluteal nerve* - The **inferior gluteal nerve** innervates the **gluteus maximus muscle**, which is also located more superiorly and laterally relative to the **ischiorectal fossa**. - Injury to this nerve would primarily affect hip extension and is not a common complication of **ischiorectal abscess** drainage.

Q: What is the preferred site for intramuscular injection in the gluteus muscle?

Superolateral. ***Superolateral*** - This quadrant is preferred because it avoids the **sciatic nerve** and major **blood vessels**, minimizing the risk of injury. - The muscle mass in this region, primarily the **gluteus medius**, is sufficient for medication absorption. *Inferomedial* - This area carries a high risk of damaging the **sciatic nerve**, which runs through the lower, medial part of the gluteus. - Injecting here can also hit major **blood vessels**, leading to bleeding or hematoma. *Superomedial* - While somewhat safer than the inferomedial quadrant, this area is still closer to the **sciatic nerve** exit point and major vessels compared to the superolateral region. - The muscle bulk is also less prominent here compared to the superolateral aspect. *Inferolateral* - This quadrant is still in the vicinity of the **sciatic nerve** and major blood vessels, making it riskier than the superolateral site. - There is less muscle mass here compared to the superior quadrants, which can lead to improper drug absorption.

Q: In sickle cell anemia, the mutation at codon 6 results in the substitution of which amino acid?

Valine for glutamic acid. ***Valine for glutamic acid*** - In **sickle cell anemia**, the normal **glutamic acid** at codon 6 of the $\beta$-globin chain is replaced by **valine**. - This single amino acid substitution is responsible for the abnormal **hemoglobin S (HbS)** and the characteristic sickling of red blood cells. *Isoleucine for valine* - This substitution is **not characteristic** of sickle cell anemia. - While other hemoglobinopathies exist, this specific change does not lead to the sickle cell phenotype. *Valine for isoleucine* - This substitution is **not the primary genetic defect** found in sickle cell anemia. - The mutation in sickle cell anemia involves the replacement of a negatively charged amino acid with a neutral one. *Glutamic acid for valine* - This represents the **reverse substitution** of what occurs in sickle cell anemia. - In sickle cell, valine replaces glutamic acid, not the other way around.

Q: What does Chargaff's rule state regarding the base pairing in DNA?

A=T, G=C. ***A=T, G=C*** - **Chargaff's rules** state that in any double-stranded DNA, the amount of **adenine (A)** is approximately equal to the amount of **thymine (T)**, and the amount of **guanine (G)** is approximately equal to the amount of **cytosine (C)**. - This equivalency reflects the specific **base pairing** in the DNA double helix, where A always pairs with T, and G always pairs with C. *A=G, T=C* - This statement is incorrect as it proposes an atypical and biologically inaccurate pairing between a **purine (A)** and another **purine (G)**, and a **pyrimidine (T)** with a **pyrimidine (C)**. - This combination would disrupt the uniform diameter of the DNA double helix required for its structural stability. *A=C, G=T* - This option is incorrect because it suggests pairing a purine (A) with a pyrimidine (C) and a purine (G) with a pyrimidine (T) in a way that is not observed in natural DNA. - Such pairings would also lead to an irregular width of the DNA molecule, destabilizing its structure. *Any combination possible* - This statement is false; base pairing in DNA is **highly specific** and not random due to chemical and structural constraints. - The specific pairing rules (**A with T, G with C**) are crucial for maintaining the consistent structure of the DNA double helix and for accurate DNA replication and transcription.

Q: What are isoenzymes?

Physically distinct forms of the same enzyme. ***Physically distinct forms of the same enzyme*** - Isoenzymes are **multiple forms of an enzyme** that catalyze the **same reaction** but differ in their **physical or biochemical properties**, such as electrophoretic mobility, optimal pH, or kinetic parameters. - These differences usually arise from **genetic variations** (different genes encoding isoforms) or **post-translational modifications** (e.g., phosphorylation, glycosylation). *Physically same forms of different enzymes* - This statement is incorrect as isoenzymes are forms of the **same enzyme**, not different enzymes. - While different enzymes can catalyze similar reactions in certain pathways, they are not referred to as isoenzymes if they are structurally identical. *Forms of same enzyme that catalyze different reactions* - This describes enzymes with **broad substrate specificity** or those that act on different substrates but are not necessarily isoenzymes. - Isoenzymes specifically catalyze the **same chemical reaction**, but they may do so with different efficiencies or under different regulatory controls. *Forms of different enzyme that catalyze same reactions* - This describes a scenario where different enzymes might exhibit **catalytic promiscuity** or broad specificity, but not isoenzymes. - Isoenzymes are always derived from the **same parent enzyme** and catalyze the identical reaction.

Q: What is the primary function of a primer in DNA replication?

Initiation of DNA replication. ***Initiation of DNA replication*** - DNA polymerase cannot synthesize new DNA strands de novo; it requires a pre-existing 3'-hydroxyl group to begin adding nucleotides. - The **primer**, a short RNA sequence, provides this necessary **3'-hydroxyl group**, allowing DNA polymerase to start synthesizing the new DNA strand. *Transcription* - This process involves synthesizing **RNA from a DNA template**, primarily carried out by **RNA polymerase**. - While primers are involved in DNA synthesis, they do not directly initiate the process of transcription. *Translation* - **Translation** is the process of synthesizing **proteins from mRNA templates** using ribosomes, tRNA, and amino acids. - This process is distinct from DNA synthesis and does not involve primers; its initiation involves start codons and ribosomal subunits. *Termination of DNA replication* - **Termination of DNA replication** occurs when replication forks meet or at specific termination sequences, often with the involvement of specialized proteins. - Primers are involved in the *start* of replication, not its conclusion.

Q: What is the cofactor required for the enzyme xanthine oxidase?

Molybdenum. ***Molybdenum*** - **Xanthine oxidase** is a key enzyme in **purine metabolism**, responsible for the oxidation of **hypoxanthine to xanthine** and further to **uric acid**. - **Molybdenum** is an essential trace element that serves as a **cofactor** for several enzymes, including xanthine oxidase, where it helps facilitate electron transfer reactions. *Selenium* - **Selenium** is a cofactor for **glutathione peroxidase**, an enzyme involved in antioxidant defense. - It is not directly involved in the function of **xanthine oxidase**. *Zinc* - **Zinc** is a cofactor for a wide range of enzymes, including **carbonic anhydrase** and **alcohol dehydrogenase**. - It does not serve as a cofactor for **xanthine oxidase**. *Magnesium* - **Magnesium** is a critical cofactor for many enzymes, particularly those involved in **ATP hydrolysis and synthesis** and **DNA/RNA synthesis**. - It is not a cofactor for **xanthine oxidase**.

Q: Which of the following is not typically associated with cystic fibrosis?

Renal failure. ***Renal failure*** - **Renal failure** is not a typical manifestation or complication of **cystic fibrosis (CF)**. The CFTR protein primarily affects epithelial cells in organs like the lungs, pancreas, liver, and intestines, not the kidneys. - While CF patients may experience **electrolyte imbalances** due to excessive salt loss, this rarely progresses to **kidney failure** as a direct result of the disease itself. *Infertility* - **Infertility** is commonly associated with CF, particularly in males due to **congenital bilateral absence of the vas deferens (CBAVD)**, which is found in over 95% of male CF patients [1]. - In females, CF can cause **viscous cervical mucus** and nutritional deficiencies, leading to challenges with conception [1]. *Azoospermia* - **Azoospermia**, specifically **obstructive azoospermia**, is a direct consequence of **congenital bilateral absence of the vas deferens (CBAVD)**, which is highly prevalent in male CF patients [1]. - This condition prevents sperm from reaching the ejaculate, despite normal sperm production in the testes. *Nasal polyps* - **Nasal polyps** are a common feature in patients with **cystic fibrosis**, often leading to **chronic rhinosinusitis** and nasal obstruction. - This is due to the dysfunctional CFTR protein leading to abnormal mucus production and inflammation in the nasal passages [1].

Q: Which of the following components are included in microcirculation?

Capillaries, venules, and arterioles. ***Capillaries, venules, and arterioles*** - **Microcirculation** is the portion of the **circulatory system** that includes the **smallest blood vessels**, specifically the **arterioles**, **capillaries**, and **venules**. - These vessels are crucial for the **delivery of oxygen** and **nutrients** to tissues and the removal of waste products. *Capillaries* - While **capillaries** are a vital part of **microcirculation** and the primary site of nutrient and waste exchange, they alone do not encompass the entire microcirculatory unit. - The microcirculation also includes the vessels that feed into and drain from the capillaries: the **arterioles** and **venules**. *Aorta* - The **aorta** is the **largest artery** in the body, part of the **macrocirculation**, which distributes blood from the heart to the systemic circulation. - It is not considered part of the **microcirculation** due to its large size and primary function as a high-pressure conduit rather than a site of exchange. *Arteries and veins* - **Arteries** and **veins** are primarily components of the **macrocirculation**, responsible for transporting blood to and from the systemic and pulmonary circuits. - While arterioles and venules (small arteries and veins) are part of the microcirculation, the broader terms "arteries" and "veins" typically refer to the larger vessels and do not exclusively define the microcirculatory network.

Q: Central stellate scar is typically associated with which of the following conditions?

Focal nodular hyperplasia (FNH). ***Focal nodular hyperplasia (FNH)*** - FNH is a benign liver lesion characterized by a central fibrous scar with radiating septa, giving it the characteristic appearance of a **central stellate scar** on imaging. - This scar contains **malformed blood vessels** and bile ductules, which are key diagnostic features. - On dynamic imaging, FNH typically shows **spoke-wheel arterial enhancement** pattern and the central scar shows **delayed enhancement** on MRI. *Hepatic adenoma* - Hepatic adenomas are typically composed of sheets of **hepatocytes** with absent portal triads and are usually **homogeneous** on imaging without a central scar. - They are associated with **oral contraceptive use** and have a risk of hemorrhage and malignant transformation. *Chronic liver disease* - Chronic liver disease, such as **cirrhosis**, is characterized by widespread **fibrosis** and **nodule formation** throughout the liver, but it does not typically present with a solitary lesion with a central stellate scar. - The scarring in cirrhosis is diffuse and leads to architectural distortion, rather than a focal central scar. *Hepatocellular carcinoma* - Hepatocellular carcinoma (HCC) typically presents as a **vascular mass** that may or may not be solitary, usually arising in the context of chronic liver disease or cirrhosis. - Although the **fibrolamellar variant of HCC** (seen in younger patients without cirrhosis) can show a central scar, this is less common and the scar typically shows **hypointensity on T2-weighted imaging**, unlike FNH where the scar is **hyperintense on T2**. - Typical HCC does not show a distinct central stellate scar as a characteristic feature.

Question 1

During incision and drainage of ischiorectal abscess, which nerve is most likely to be injured?

Accepted Answer

Inferior rectal nerve

Answer

Superior rectal nerve

Answer

Superior gluteal nerve

Answer

Inferior gluteal nerve

Question 2

What is the preferred site for intramuscular injection in the gluteus muscle?

Accepted Answer

Superolateral

Answer

Inferolateral

Answer

Superomedial

Answer

Inferomedial

Question 3

In sickle cell anemia, the mutation at codon 6 results in the substitution of which amino acid?

Accepted Answer

Valine for glutamic acid

Answer

Isoleucine for valine

Answer

Valine for isoleucine

Answer

Glutamic acid for valine

Question 4

What does Chargaff's rule state regarding the base pairing in DNA?

Accepted Answer

A=T, G=C

Answer

A=G, T=C

Answer

A=C, G=T

Answer

Any combination possible

Question 5

What are isoenzymes?

Accepted Answer

Physically distinct forms of the same enzyme

Answer

Physically same forms of different enzymes

Answer

Forms of same enzyme that catalyze different reactions

Answer

Forms of different enzyme that catalyze same reactions

Question 6

What is the primary function of a primer in DNA replication?

Accepted Answer

Initiation of DNA replication

Answer

Transcription

Answer

Translation

Answer

Termination of DNA replication

Question 7

What is the cofactor required for the enzyme xanthine oxidase?

Accepted Answer

Molybdenum

Answer

Selenium

Answer

Zinc

Answer

Magnesium

Question 8

Which of the following is not typically associated with cystic fibrosis?

Accepted Answer

Renal failure

Answer

Infertility

Answer

Azoospermia

Answer

Nasal polyps

Question 9

Which of the following components are included in microcirculation?

Accepted Answer

Capillaries, venules, and arterioles

Answer

Capillaries

Answer

Aorta

Answer

Arteries and veins

Question 10

Central stellate scar is typically associated with which of the following conditions?

Accepted Answer

Focal nodular hyperplasia (FNH)

Answer

Hepatic adenoma

Answer

Chronic liver disease

Answer

Hepatocellular carcinoma

NEET-PG 2012

Anatomy

Biochemistry

Internal Medicine

Physiology

Radiology