INI-CET High Yield Questions For Biochemistry

Mastering the INI-CET demands a strategic approach to preparation, with an emphasis on high-yield topics proving to be a successful tactic. This blog zeroes in on exactly that – a curated list of high-yield questions in Biochemistry that are highly likely to appear on the INI-CET. By acquainting yourself with these questions and their detailed explanations, you'll deepen your understanding of Biochemistry concepts, enhancing your confidence and readiness for exam day.

1. A 28-year-old man presented to the hospital complaining of intractable vomiting and inability to eat or drink for the past 3 days. His blood analysis still shows a normal glucose level. Which of the following processes is mainly responsible for the blood glucose maintenance in this patient?

A. Liver gluconeogenesis

B. Dietary Glucose

C. Muscle glycogenolysis

D. Liver glycogenolysis

Correct Option A - Liver gluconeogenesis:

• In starvation, when the patient hasn't eaten for 3 days, the liver produces glucose via glycogenolysis initially.
• As fasting continues, glycogen depletes, and the liver synthesizes glucose through gluconeogenesis using lactate, pyruvate, glycerol, and amino acids.
• Glucagon released during starvation activates gluconeogenic enzymes in the liver, maintaining blood glucose levels necessary for vital organs like the brain, heart, and RBCs.
• Thus, liver gluconeogenesis predominates in prolonged fasting, contrasting with glycogen metabolism in the fed state and gluconeogenesis from substrates during fasting.

Adaptations during starvation
Fed state	Skeletal Muscle	Cardiac Muscle
Preferred fuel at rest	Fatty acids	FFA, ketone bodies, lactate
Exercise	Glycogen to lactate	Fatty acids
Starvation Adaptations	Protein breakdown; release of amino acids; FFA, ketone bodies, and branched-chain amino acids utilized	Fatty acids, branched-chain amino acids, and ketone bodies utilized

Incorrect Options:

Option B - Dietary Glucose:

• Dietary glucose can provide blood glucose up to 2 hours after feeding.

Option C - Muscle glycogenolysis:

• The glycogenolysis inside the muscles leads to glucose-6-phosphate as an end-product, not D-Glucose, due to the absence of the enzyme glucose-6-phosphatase in muscles. Hence, muscle glycogen cannot contribute to blood glucose directly.

Option D - Liver glycogenolysis:

• Glycogen breakdown in the liver can maintain blood glucose for 12-18 hours.

2. In the graph below, Curve A is obtained for liver glucokinase, while Curve B is for muscle glucokinase under similar conditions.

A. A is the same enzyme as B but in the presence of a competitive inhibitor

B. B has a greater affinity for glucose than A.

C. At maximal substrate concentrations, both enzymes display first-order kinetics.

D. B has a higher Michaelis-Menten constant (K_m) than A.

Correct Option D - B has a higher Michaelis-Menten constant (K_m) than A:

• B has a higher Michaelis-Menten constant (Km) than A.
• Km is determined from substrate concentration at half of enzyme's Vmax.

• The graph indicates B's higher Km as it has higher Vmax compared to A.

Incorrect Options:

Option A - A is the same enzyme as B but in the presence of a competitive inhibitor:

• A is the same enzyme as B but with a competitive inhibitor. If so, both would have equal Vmax, contrary to the graph.

Option B - B has a greater affinity for glucose than A:

• B has greater glucose affinity than A. Affinity relates to lower Km; hence, A's lower Km implies higher affinity for glucose.

Option C - At maximal substrate concentrations, both enzymes display first-order kinetics:

• Both enzymes display first-order kinetics at maximal substrate concentrations. Yet, at this point, enzyme binding sites are saturated, suggesting zero-order kinetics, not first-order.

3. A 40-year-old male presents to the emergency department due to red urine, skin rash, photosensitivity, and blisters for the past several months. These skin lesions are present in areas exposed to the sun. A picture of the urine sample is given below. Which of the following enzymes is most likely deficient?

A. Porphobilinogen deaminase

B. Uroporphyrinogen decarboxylase

C. Ferrochelatase

D. Aminolevulinate dehydratase

Correct Option B - Uroporphyrinogen decarboxylase:

• Patient likely has porphyria cutanea tarda, evident from red-brown or tea-colored urine and sun-exposed skin lesions.
• Porphyria cutanea tarda is an adult-onset hepatic porphyria caused by deficient uroporphyrinogen decarboxylase activity, leading to impaired heme synthesis.
• Uroporphyrin leakage into urine causes the characteristic coloration.
• Exacerbating factors include elevated alcohol and iron levels.
• Skin lesions result from elevated porphyrin levels; beta-carotene reduces lesions by decreasing reactive oxygen species.
• Treatment involves phlebotomy, sun protection, and drugs like hydroxychloroquine.
• Patients may exhibit mildly elevated liver function tests.

Incorrect Options:

Option A - Porphobilinogen deaminase:

• Incorrect. It causes acute intermittent porphyria with acute abdominal pain, not skin findings.
• Red-tinged urine in this condition darkens upon exposure to air or light due to biochemical oxidation.

Option C - Ferrochelatase:

• Incorrect. Lead inhibition leads to increased protoporphyrin levels, causing symptoms like abdominal pain and CNS effects, not urine color changes.

Option D - Aminolevulinate dehydratase:

• Incorrect. Lead poisoning inhibits this enzyme, presenting with abdominal pain and CNS symptoms, but no urine color change.

Also Read: INI-CET Previous Year Question Papers

4. A woman develops anemia in the 6^th month of her first pregnancy. Blood workup reveals hyper-segmented neutrophils with increased mean cell volume (MVC), morphological alterations in other cell types, and elevated serum levels of homocysteine. Which of the following is the most likely cause of anemia in this woman?

A. Folate deficiency

B. Iron deficiency

C. Glucose 6-phosphate dehydrogenase deficiency

D. Lead poisoning

Correct Option A - Folate deficiency:

• Symptoms: Hyper-segmented neutrophils, increased mean cell volume (MVC), morphological changes in other cells.
• Mechanism: Folate needed for DNA synthesis; deficiency leads to delayed cell division, forming abnormally large cells (megaloblastic anemia).
• Homocysteine: Elevated due to impaired conversion to methionine.
• Affected cells: Rapidly dividing cells like bone marrow and intestinal mucosa.
• Diagnostic markers: Elevated homocysteine; normal methylmalonic acid.
• Prevention: Folate supplements before conception reduce neural tube defects.

Incorrect Options:

Option B - Iron deficiency:

• It presents as microcytic hypochromic anemia and would not elevate homocysteine.

Option C - Glucose 6-phosphate dehydrogenase deficiency:

• It is associated with hemolytic anemia that occurs secondary to:
  • Exposure to some drugs such as dapsone, sulfa drugs, and nitrofurantoin
  • Infections
  • Ingestion of fava beans

Option D - Lead poisoning:

• Lead inhibits heme synthesis by inhibiting enzymes ALA dehydratase and ferrochelatase resulting in microcytic and hypochromic anemia.

5. A 10-day-old neonate was brought to the emergency department with complaints of vomiting, irritability, difficulty in feeding, and somnolence. On investigation, there is decreased blood urea nitrogen and increased orotic acid in the blood. No megaloblastic anemia is seen. Which enzyme deficiency leads to this condition?

A. Ornithine transcarbamoylase (OTC)

B. Ornithine aminotransferase

C. Uridine monophosphate (UMP) synthase

D. Hypoxanthine guanine phosphoribosyltransferase (HGPRT)

Correct Option A - Ornithine transcarbamoylase (OTC):

• Consistent with OTC deficiency, an X-linked disorder primarily affecting males.
• Impairs urea synthesis, leading to hyperammonemia after birth.
• Symptoms include vomiting, irritability, feeding difficulties, tremors, and coma in severe cases.
• Most common urea cycle disorder.
• Laboratory findings: decreased BUN, increased orotic acid due to carbamoyl phosphate diversion.
• Diagnosis involves clinical, laboratory, and genetic testing, distinguishing from UMPS deficiency causing megaloblastic anemia but not hyperammonemia.

Incorrect Options:

Option B - Ornithine aminotransferase:

• Catalyzes a different reaction, not affecting the urea cycle.
• Deficiency results in gyrate atrophy, characterized by elevated ornithine levels.

Option C - UMP synthase:

• Deficiency leads to orotic acid accumulation and megaloblastic anemia.
• Differentiates from OTC by lacking hyperammonemia.

Option D - HGPRT deficiency:

• Causes Lesch-Nyhan syndrome with hyperuricemia and self-mutilation behavior.

6. Arrange the following enzyme categories as per increasing order of their enzyme commission numbers:

1. Isomerases

2. Hydrolases

3. Oxidoreductase

4. Transferases

A. 1→ 3 → 4 → 2

B. 3→ 4 → 2 → 1

C. 3→ 2 → 4→ 1

D. 2→ 4→ 1 → 3

Correct  Option B - 3→ 4 → 2 → 1:

• The Enzyme Commission number (EC number) categorizes enzymes based on their catalyzed chemical reactions.
• Each EC number corresponds to a recommended name for the enzyme-catalyzed reaction.
• EC numbers classify reactions, not enzymes themselves. Different enzymes catalyzing the same reaction receive the same EC number.
• The enzyme categories, in increasing order of EC number, are Oxidoreductases → Transferases → Hydrolases → Isomerases. Hence, 3→ 4 → 2 → 1 is the correct sequence.

Class	Designation	Function
EC1	Oxidoreductases	Catalyze oxidation/reduction reactions
EC2	Transferases	Transfer a functional group (e.g., a methyl or phosphate group)
EC3	Hydrolases	Catalyze the hydrolysis of various bonds
EC4	Lyases	Cleave various bonds by means other than hydrolysis and oxidation
EC5	Isomerases	Catalyze isomerization changes within a single molecule
EC6	Ligases	Join two molecules through covalent bonds

Incorrect Options:

Option A, C, and D: Refer to the explanation

7. Which enzyme is responsible for the simultaneous processes of oxidation and decarboxylation, resulting in the release of carbon dioxide (CO2) and the generation of NADH?

A. Alpha-ketoglutarate dehydrogenase

B. Malate dehydrogenase

C. Succinate dehydrogenase

D. Fumarase

Correct Option A - Alpha-ketoglutarate dehydrogenase:

• The simultaneous removal of electrons and CO₂ from a substrate is called oxidative decarboxylation.
• There are total 4 dehydrogenases present in Kreb's cycle:
  1. Isocitrate dehydrogenase (IDH)
  2. α- Ketoglutarate dehydrogenase complex (α-KG DH)
  3. Succinate dehydrogenase
  4. Malate dehydrogenase
• Out of them, two catalyze oxidative decarboxylation reactions:
  1. Isocitrate dehydrogenase
  2. α-ketoglutarate dehydrogenase

Incorrect Options:

Option B - Malate dehydrogenase:

• Catalyzes simple dehydrogenation of malate to regenerate TCA carrier oxaloacetate
• Use NAD as a coenzyme to transfer electrons from the substrate

Option C - Succinate dehydrogenase:

• Catalyzes simple dehydrogenation of succinate to form Fumarate
• Use prosthetic group FAD to transfer electrons from the substrate
• It is the only membrane-bound enzyme of TCA and is also called respiratory complex II

Option D Fumarase:

• Catalyzes the formation of malate from Fumarate
• It is a hydration reaction, i.e., adding water across a double bond to introduce an -OH group. So, this enzyme is not a dehydrogenase

8. An investigator is studying the mode of inheritance in a particular disease. He finds that all the daughters and sons of an affected mother have the disease. On the other hand, none of the daughters or the sons of an affected father have the disease. Which of the following disorders is not an example of such a type of inheritance?

A. MELAS

B. Leber hereditary optic neuropathy

C. NARP syndrome

D. Incontinentia pigmenti

Correct Option D - Incontinentia pigmenti:

• In mitochondrial inheritance disorders, all the daughters and sons of an affected mother will have the disease but none of the daughters or the sons of an affected father have the disease.
• Examples of Mitochondrial Inheritance Disorders

Leber hereditary optic neuropathy

• NARP syndrome – Neuropathy, Ataxia & Retinitis Pigmentosa
• MERRF - Myoclonic epilepsy with ragged-red fibers
• MELAS– Mitochondrial Encephalopathy, Lactic Acidosis, and Stroke-like episodes

Incontinentia pigmenti (Bloch-Sulzberger syndrome)

• Has an X-linked dominant pattern of inheritance
• C/f are blistering rash in infancy followed by wart-like skin growths
• Hair, teeth & CNS manifestations

Incorrect Options:Option A, B and C are incorrect and the correct option has been explained above.

9. What is the name of the process described in the image, and also identify the bonds broken?

A, Denaturation, Hydrogen bonds

B. Denaturation, 3’-5' Phosphodiester bonds

C. Hybridization, Beta-N-Glycosidic bonds

D. Denaturation, Covalent bonds

Correct Option A - Denaturation, Hydrogen bonds:

• DNA consists of two strands forming a double helix.
• The backbone of DNA is composed of deoxyribose sugar molecules linked by phosphodiester bonds.
• Nitrogenous bases (adenine, thymine, cytosine, guanine) form complementary pairs across the helix: A-T and G-C.
• Hydrogen bonds connect the base pairs: two between A-T and three between G-C.
• Denaturation or melting of DNA involves the separation of the two strands by breaking the hydrogen bonds between the base pairs.
• Hydrogen bonds are weaker than covalent bonds (phosphodiester and glycosidic bonds), making them susceptible to disruption under various conditions like temperature or pH changes.
• Phosphodiester and glycosidic bonds are strong covalent bonds and are not affected by denaturation.

Incorrect Options:

Option B - Denaturation, 3’-5' phosphodiester bonds:

• Denaturation is due to the breakage of hydrogen bonds.
• Phosphodiester bonds are strong covalent bonds and are not broken by temperature or pH changes during the DNA denaturation process.

Option C - Hybridization, Beta-N-Glycosidic bonds:

• Hybridization is the process when two complementary individual DNA or RNA strands join together by hydrogen bonds. It is the reversal of denaturation
• Beta-N-Glycosidic bonds are present between the ring sugar molecule and a nitrogenous base. It is a covalent bond not affected during denaturation.

Option D - Denaturation, Covalent bonds:

• Denaturation occurs when the weak hydrogen bonds between nitrogenous bases break. Covalent bonds are much stronger than hydrogen bonds and do not break during denaturation.

10. A researcher is studying the process of gene expression in different cells of the body. His finding points out that although all the cells of the body have the same genetic information in their nucleus the genetic material is selectively expressed depending on the specific type and function of the cell in the tissue. The figure below shows the technique used by the researcher for this purpose. Which of the following genetic techniques is shown in the figure?

A. CRISPR - CAS system

B. Microarray

C. RNA interference

D. RFLP

Correct Option B – Microarray:

• The figure shows the technique of DNA microarrays.
• DNA microarrays consist of thousands of short DNA sequences arranged on a glass or silicon chip.
• Samples of DNA or RNA are labeled with fluorescent dyes and hybridized with the DNA sequences on the array.
• The relative fluorescence indicates the level of hybridization between the samples.
• Microarrays are utilized to measure and compare gene expression, as well as for clinical genetic testing, genotyping, cancer mutation typing, and genetic linkage analysis.

Incorrect Options:

Option A, C, and D:

• The image in the vignette represents the genetic technique of Microarrays.
• The CRISPR-Cas system edits genes by utilizing Cas9 guided by RNA with complementary bases to target DNA sections.
• RNA interference silences mRNA using microRNA.
• Restriction fragment length polymorphism identifies DNA polymorphisms using restriction endonucleases that cut at palindromic sites.

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