INI-CET 2026 Practice Questions

Q: Which of the following enzymes are active in the dephosphorylated state? 1. Glycogen synthase 2. Glycogen phosphorylase 3. Fructose-2,6-bisphosphatase 4. Phosphofructokinase-2 (PFK-2)

1 and 4. ***1 and 4*** - **Glycogen synthase** is activated by dephosphorylation (via **Protein Phosphatase-1**) in response to **insulin**, promoting glycogenesis. - **Phosphofructokinase-2 (PFK-2)** is active in its dephosphorylated state, where its **kinase domain** predominates to produce **Fructose-2,6-bisphosphate**, stimulating glycolysis. *1 and 2* - **Glycogen synthase** is indeed active when dephosphorylated, but **Glycogen phosphorylase** is the opposite; it requires phosphorylation (by **phosphorylase kinase**) to become active for glycogenolysis. - This pair incorrectly groups an enzyme activated by dephosphorylation with one activated by phosphorylation. *2 and 3* - **Glycogen phosphorylase** and **Fructose-2,6-bisphosphatase** are both enzymes that are active in their **phosphorylated** states. - They function during fasting states (mediated by **glucagon/epinephrine** and **protein kinase A**) to promote glycogen breakdown and gluconeogenesis, respectively. *3 and 4* - **Fructose-2,6-bisphosphatase** is active only when phosphorylated, which activates its phosphatase domain to lower levels of **Fructose-2,6-bisphosphate**. - Conversely, **PFK-2** is inactive when phosphorylated, making this option incorrect as it pairs an enzyme inactive in the dephosphorylated state with one active in it.

Q: In DNA replication, which enzyme synthesizes RNA primers?

Primase. ### ***Primase*** - **Primase** is an **RNA polymerase** that synthesizes short **RNA primers** (approximately 10-12 nucleotides long) to provide a free **3'-OH group** needed by **DNA polymerase** to initiate synthesis. - Without this primer, **DNA replication** cannot begin because **DNA polymerases** lack the ability to start synthesizing a new strand *de novo*. *Topoisomerase* - **Topoisomerases** (such as **DNA gyrase**) are responsible for relieving **supercoiling** and **torsional strain** in the DNA helix ahead of the replication fork. - They do not possess **primase** activity and do not participate in synthesizing the RNA primer. *DNA polymerase II* - **DNA polymerase II** is primarily involved in **DNA repair** mechanisms, specifically in replicating through damaged DNA segments. - It lacks the catalytic ability to synthesize RNA primers and is not a replication initiator. *DNA polymerase III* - **DNA polymerase III** is the primary enzyme responsible for the **elongation** of the leading and lagging strands, adding nucleotides to the existing primer. - While it is essential for synthesizing the bulk of the new DNA, it requires a preexisting primer to function and cannot generate one itself.

Q: Which of the following amino acid classifications are correctly matched? 1. Uncharged polar AA - Cysteine 2. Nonpolar AA - Histidine 3. Basic AA - Proline 4. Basic AA - Lysine

A and D. ***A and D*** - **Cysteine** is correctly classified as an **uncharged polar amino acid** because it contains a sulfhydryl (-SH) group that is weakly polar. - **Lysine** is correctly classified as a **basic amino acid** due to the presence of an amino group in its side chain, which carries a positive charge at physiological pH. *A and B* - This option is incorrect because, while Cysteine is correctly identified, **Histidine** is classified as a **basic amino acid**, not a nonpolar one, due to its imidazole ring. *C and D* - This option is incorrect because **Proline** is classified as a **nonpolar amino acid**, not a basic one; its unique cyclic structure makes it rigid and hydrophobic. *B and C* - This option is incorrect because both classifications provided are wrong: **Histidine** is **basic** and **Proline** is **nonpolar**.

Q: A newborn presents with craniofacial abnormalities, severely reduced muscle tone, and seizures. Biochemical analysis reveals elevated very long chain fatty acids in serum. What is the most likely underlying cause?

Peroxisomal biogenesis defect. ***Peroxisomal biogenesis defect*** - The classic presentation of **Zellweger syndrome**, a peroxisomal biogenesis disorder, includes craniofacial abnormalities (e.g., high forehead, large anterior fontanelle), profound hypotonia, and seizures in the neonatal period. - This condition is caused by mutations in **PEX genes**, leading to the absence of functional peroxisomes and the subsequent **accumulation of very long chain fatty acids (VLCFAs)** in the serum. *Mitochondrial inheritance* - Mitochondrial disorders typically present with symptoms such as lactic acidosis, myopathy, or encephalopathy, but they do not specifically cause the elevation of VLCFAs. - Inherited via **maternal lineage**, these defects usually involve defects in the electron transport chain rather than fatty acid oxidation pathways. *Lysosomal storage disorder* - These disorders are characterized by the accumulation of substrates due to deficient enzymes within lysosomes, as seen in conditions like Gaucher or Tay-Sachs disease. - They generally present with progressive organomegaly (e.g., hepatosplenomegaly) and neurodegeneration rather than the characteristic craniofacial dysmorphism and VLCFA elevation seen in peroxisomal defects. *Simultaneously activate multiple tumor suppressor genes* - This is not a mechanism related to metabolic storage diseases or peroxisomal function. - Tumor suppressor gene activation is a concept associated with cancer genetics and abnormal cell growth, not metabolic enzyme deficiencies.

Q: The image shown depicts a piece of sterilization equipment. Which of the following statements regarding its sterilization properties is INCORRECT?

Prions are completely destroyed at 121°C for 15 minutes. ***Prions are completely destroyed at 121°C for 15 minutes*** - This statement is **incorrect** because **prions** are highly resistant to standard autoclaving protocols; they generally require more stringent methods such as **134°C** for 18 minutes in a pre-vacuum autoclave or specific chemical treatments like sodium hydroxide. - The standard cycle of **121°C for 15 minutes** is designed for vegetative bacteria, fungi, and viruses, but it is insufficient to denature the misfolded proteins associated with **prion diseases**. *It is a method of moist heat sterilization operating above 100°C* - The equipment shown is an **autoclave**, which utilizes **pressurized steam** to achieve temperatures significantly higher than the boiling point of water. - This elevated temperature effectively kills microorganisms through the **coagulation of cellular proteins** and enzymes, confirming the accuracy of this statement. *Bowie-Dick test positive* - While the test itself is designed to detect air leaks and ensure proper steam penetration for a successful cycle, saying

Q: A 32-year-old woman with a history of splenectomy presents to the emergency department with sudden-onset high-grade fever, vomiting, hypotension, and rapidly progressive septic shock. Her symptoms began 2 weeks after a minor febrile illness. Which organism is the most likely causative agent of this life-threatening condition?

Streptococcus pneumoniae. ***Streptococcus pneumoniae*** - Patients with **asplenia** (post-splenectomy) are at significantly increased risk for overwhelming post-splenectomy infection (OPSI) due to defective clearance of **encapsulated organisms**. - *Streptococcus pneumoniae* is the most common cause of sepsis in asplenic patients, characterized by fulminant disease progression, high mortality rates, and rapid development of **septic shock**. *Escherichia coli* - While *Escherichia coli* is a common cause of sepsis (particularly urosepsis and intra-abdominal infections), it is not the classic pathogen associated with the unique susceptibility of the **asplenic patient**. - It lacks the specific capsular polysaccharide susceptibility profile that makes *S. pneumoniae* the primary concern in individuals without a functional **spleen**. *Staphylococcus aureus* - *Staphylococcus aureus* is a leading cause of skin and soft tissue infections, endocarditis, and osteomyelitis, but it is not typically characterized as an **encapsulated organism** that targets asplenic individuals. - The clinical presentation of rapid-onset septic shock following minor illness is more classic for the **fulminant course** of a pneumococcal infection in this specific patient demographic. *Pseudomonas aeruginosa* - *Pseudomonas aeruginosa* is an important cause of sepsis especially in **immunocompromised** or hospitalized patients, but it is not the most frequent pathogen associated with asplenia. - It generally presents in settings such as **ventilator-associated pneumonia**, burn wounds, or neutropenic fever, rather than the classic OPSI syndrome triggered by circulating **encapsulated bacteria**.

Q: Which of the following reagents is used for the digestion and decontamination of a sputum sample collected for tuberculosis diagnosis?

NaOH with NALC. ***NaOH with NALC*** - **Sodium hydroxide (NaOH)** acts as a potent decontaminating agent that kills rapidly growing commensal flora present in the sputum, allowing for the selective growth of *Mycobacterium tuberculosis*. - **N-acetyl-L-cysteine (NALC)** serves as a mucolytic agent, digesting the sputum matrix and liquefying the sample so that the mycobacteria are released and can be concentrated via centrifugation. *HCl with NAC* - **Hydrochloric acid (HCl)** is not effectively used combined with NAC for primary sputum decontamination in standard **tuberculosis** culture protocols. - While acids can be used for decontamination, this specific combination is not the standard clinical reagent for *Mycobacterium tuberculosis* processing. *H2SO4 with NAC* - **Sulfuric acid (H2SO4)** is sometimes used in specific decontamination protocols (Petroff's method uses NaOH, but acid-based methods exist), but this is not the preferred or most common reagent pair known for this purpose. - Furthermore, **NAC** (N-acetylcysteine) is distinct from **NALC** (N-acetyl-L-cysteine), which is the standard, more effective mucolytic agent chosen for clinical lab processing. *HNO3 with NALC* - **Nitric acid (HNO3)** is a strong corrosive acid, not a standard reagent for the clinical decontamination of sputum samples for mycobacterial culture. - Using such a harsh chemical could risk killing the **mycobacteria** themselves, decreasing the sensitivity of the diagnostic test.

Q: A patient presents with fever, headache, and neck stiffness suggestive of meningitis. CSF examination is performed, and Nigrosin stain reveals encapsulated budding yeast cells. Which of the following organisms is the most likely causative agent?

Cryptococcus neoformans. ***Cryptococcus neoformans*** - This organism is characterized as an **encapsulated budding yeast** that is classically identified in **cerebrospinal fluid (CSF)** using **India ink** or **Nigrosin stain**. - It is the most common cause of fungal meningitis, particularly in **immunocompromised patients** (e.g., those with AIDS), and the capsule appears as a clear halo against the dark background of the stain. *Aspergillus fumigatus* - This is a **mold** that typically presents as **septate hyphae** with acute-angle (45-degree) branching, not as budding yeast. - While it can invade the central nervous system, it usually causes **abscesses** or **vascular invasion** rather than the typical yeast-like presentation in CSF. *Pneumocystis jirovecii* - This organism is an **atypical fungus** that does not grow in culture and is typically identified in lung tissue or bronchoalveolar lavage fluid using **Methenamine silver stain**. - It classically causes **interstitial pneumonia** in immunocompromised hosts and does not typically infect the meninges as a budding yeast. *Histoplasma capsulatum* - This is a **dimorphic fungus** that exists as small, intracellular yeast forms within **macrophages** in host tissues. - It is typically identified via biopsy or antigen testing, not as an encapsulated yeast in the CSF, and usually presents with systemic symptoms like hepatosplenomegaly or pulmonary involvement.

Question 1

Which of the following enzymes are active in the dephosphorylated state?
1. Glycogen synthase
2. Glycogen phosphorylase
3. Fructose-2,6-bisphosphatase
4. Phosphofructokinase-2 (PFK-2)

Accepted Answer

1 and 4

Answer

1 and 2

Answer

2 and 3

Answer

3 and 4

Question 2

In DNA replication, which enzyme synthesizes RNA primers?

Accepted Answer

Primase

Answer

Topoisomerase

Answer

DNA polymerase II

Answer

DNA polymerase III

Question 3

Which of the following amino acid classifications are correctly matched?
1. Uncharged polar AA - Cysteine
2. Nonpolar AA - Histidine
3. Basic AA - Proline
4. Basic AA - Lysine

Accepted Answer

A and D

Answer

A and B

Answer

C and D

Answer

B and C

Question 4

A newborn presents with craniofacial abnormalities, severely reduced muscle tone, and
seizures. Biochemical analysis reveals elevated very long chain fatty acids in serum. What is the
most likely underlying cause?

Accepted Answer

Peroxisomal biogenesis defect

Answer

Mitochondrial inheritance

Answer

Lysosomal storage disorder

Answer

Simultaneously activate multiple tumor suppressor genes

Question 5

A laboratory worker accidentally inhales fumes of an oxidative phosphorylation uncoupling
agent. Which of the following physiological changes is most likely to occur?

Accepted Answer

increased O2 consumption, increased Body temperature, decreased ATP production

Answer

decreased O2 consumption, increased Body temperature, increased ATP production

Answer

increased O2 consumption, decreased Body temperature, increased ATP production

Answer

decreased O2 consumption, decreased Body temperature, decreased ATP production

Question 6

The image shown depicts a piece of sterilization equipment. Which
of the following statements regarding its sterilization properties is
INCORRECT?

Accepted Answer

Prions are completely destroyed at 121°C for 15 minutes

Answer

It is a method of moist heat sterilization operating above 100°C

Answer

Bowie-Dick test positive

Answer

It is commonly used for sterilizing culture media

Question 7

A 32-year-old woman with a history of splenectomy presents to the emergency department with
sudden-onset high-grade fever, vomiting, hypotension, and rapidly progressive septic shock. Her
symptoms began 2 weeks after a minor febrile illness. Which organism is the most likely causative
agent of this life-threatening condition?

Accepted Answer

Streptococcus pneumoniae

Answer

Escherichia coli

Answer

Staphylococcus aureus

Answer

Pseudomonas aeruginosa

Question 8

Which of the following reagents is used for the digestion and decontamination of a sputum
sample collected for tuberculosis diagnosis?

Accepted Answer

NaOH with NALC

Answer

HCl with NAC

Answer

H2SO4 with NAC

Answer

HNO3 with NALC

Question 9

A patient presents with fever, headache, and neck stiffness suggestive of meningitis. CSF
examination is performed, and Nigrosin stain reveals encapsulated budding yeast cells. Which of
the following organisms is the most likely causative agent?

Accepted Answer

Cryptococcus neoformans

Answer

Aspergillus fumigatus

Answer

Pneumocystis jirovecii

Answer

Histoplasma capsulatum

Question 10

A female presents with high grade fever, diffuse erythematous rash and hypotension. She is
currently menstruating and using tampoons. The toxin responsible acts by?

Accepted Answer

Vbeta region of the T-cell receptor and MHC class II molecule

Answer

MHC class I molecule only

Answer

CD4 receptor only

Answer

B-cell receptor and IgG

INI-CET 2026

Biochemistry

Microbiology