Biochemistry Important Questions For NEET PG/FMG Exams

Biochemistry as a subject for NEET PG/ FMGE plays a vital role in you acing the exam. Studying this subject thoroughly enhances your understanding of core concepts. If you wish to connect clinical relevance with foundational science, focusing on the subject is the safest bet.

We understand how daunting it can be to tackle the subject as it covers complex topics including metabolic disorders, complex pathways, and enzyme functions. To make it a tad easier and manageable for you, we have curated a list of high-yield Biochemistry questions that are sure to enhance your understanding.

Each question covers high-yield topics and comes with explanations that clarify concepts and aid retention. Whether you are starting your preparation from scratch or just brushing up your knowledge, these questions will help you in mastering biochemistry for your upcoming exams.

Q.1 Which of the following toxins directly inhibits the activity of the enzyme aconitase in the Citric Acid Cycle?

1. Cyanide 
2. Fluoroacetate 
3. Rotenone
4. Antimycin A

Answer: 2) Fluoroacetate

Explanation: Fluoroacetate is a plant-based toxin that inhibits the activity of the enzyme aconitase in the citric acid cycle.

Fluoroacetyl-CoA condenses with oxaloacetate to form fluorocitrate, which inhibits the aconitase enzyme, causing citrate accumulation. 

Inhibitors of enzymes involved in the citric acid cycle:

Inhibitor	Enzyme	Result
Fluoroacetate	Aconitase	Accumulation of citrate
Arsenite	Alpha-ketoglutarate dehydrogenase complex	Accumulation of alpha-ketoglutarate
Malonate	Succinate dehydrogenase	Accumulation of succinate

Also read: Important Questions On Carbohydrate Chemistry

Q.2 A 45-year-old male presents with fatigue and pallor. Blood tests reveal hemolytic anemia. On further investigation, it is found that his erythrocytes are susceptible to oxidative damage. What is the primary role of the pentose phosphate pathway (PPP) that is deficient in this patient’s RBCs?

1. To produce ATP for energy metabolism
2. To generate ribose-5-phosphate for nucleotide synthesis
3. To provide NADPH for maintaining reduced glutathione levels
4. To synthesize hemoglobin

Answer: 3) To provide NADPH for maintaining reduced glutathione levels

Explanation:

The pentose phosphate pathway (PPP) is essential in erythrocytes because it generates NADPH. NADPH is crucial for maintaining glutathione in its reduced form, which is necessary for the activity of glutathione peroxidase. This enzyme removes harmful hydrogen peroxide (H₂O₂), protecting red blood cells from oxidative damage and preventing hemolysis.

Q.3 Which of the following statements regarding the electron transport chain (ETC) is incorrect?

1. Electrons from NADH enter the ETC through Complex I 
2. Complex II is the only complex that does not pump protons.  
3. Coenzyme Q and cytochrome c transfer electrons between complexes 
4. Complex IV is the only complex that contains iron-sulfur proteins. 

Answer: 4) Complex IV is the only complex that contains iron-sulfur proteins. 

Explanation:

All electron transport chain complexes contain iron-sulfur proteins except for Complex IV (cytochrome c oxidase), which contains copper.

Also read: Important Topics in Biochemistry for NEET-PG

Q.4 Match the lipoprotein with its function.

Lipoprotein	Function
1. Chylomicron	a. Transports triglycerides from the liver to muscle and adipose tissue
2. Very low-density lipoprotein (VLDL)	b. Transports cholesterol from peripheral tissue to the liver
3. Low-density lipoprotein (LDL)	c. Transports cholesterol from the liver to peripheral tissues
4. High-density lipoprotein (HDL)	d. Transports triglycerides from the gut to liver, muscle and adipose tissue

1. 1-d,2-a,3-c,4-b
2. 1-a,2-b,3-c,4-d
3. 1-a,2-b,3-d,4-c
4. 1-c,2-d,3-b,4-a

Answer: 1) 1-d,2-a,3-c,4-b

Explanation:

Since lipids are insoluble in water, they are transported in blood as lipoproteins 

Lipoprotein	Function
Chylomicron	Transports triglycerides from the gut to liver, muscle and adipose tissue
Very low-density lipoprotein (VLDL)	Transports triglycerides from the liver to muscle and adipose tissue
Intermediate-density lipoprotein (IDL)	VLDL remnant
Low-density lipoprotein (LDL)	Transports cholesterol from the liver to peripheral tissues
High-density lipoprotein (HDL)	Transports cholesterol from peripheral tissue to the liver

Q.5 A premature baby presents with infant respiratory distress syndrome. The neonatologist says the neonate is yet to produce a type of phospholipid adequately. All of the following belong to the same class except?

1. Cephalin
2. Cardiolipin
3. Lecithin
4. Cerebrosides

Answer: 4) Cerebrosides

Explanation:

The neonate in respiratory distress syndrome fails to produce lecithin (phosphatidylcholine), a phospholipid crucial for surfactant production. Cephalin, cardiolipin, and lecithin are all phospholipids.

Cerebroside is a glycolipid and not a phospholipid.

Q.6 A 30-year-old woman presents with a history of four consecutive miscarriages over the past three years. After a thorough evaluation, a diagnosis  is made . Which of the following phospholipids is specifically antigenic in this disease?

1. Phosphatidylserine
2. Phosphatidylinositol
3. Cardiolipin
4. Phosphatidylethanolamine

Answer: 3) Cardiolipin

Explanation:

• The condition described is Antiphospholipid Syndrome (APS), a disorder characterized by recurrent miscarriages, thrombosis, and the presence of antiphospholipid antibodies.
• Cardiolipin is a phospholipid that becomes antigenic in Antiphospholipid Syndrome, leading to the production of anti-cardiolipin antibodies.
• Other phospholipids (Phosphatidylserine, Phosphatidylinositol, and Phosphatidylethanolamine) are not antigenic.

Also read: Amino Acid Protein Chemistry

Q.7 Which of the following pathways is primarily involved in the detoxification of ammonia in the brain?

1. Conversion of ammonia to urea in neurons
2. Direct excretion of ammonia through the blood-brain barrier
3. Conversion of ammonia to glutamine via glutamine synthetase in astrocytes
4. Storage of ammonia in neurons as glutamate

Answer: 3) Conversion of ammonia to glutamine via glutamine synthetase in astrocytes

Explanation:

Glutamine synthetase in astrocytes converts glutamate and ammonia to glutamine, effectively detoxifying ammonia in the brain.

Ammonia Management in Neurons:

Ammonia can be neurotoxic if accumulated.

Glutamine Synthesis:

• Produced in neurons as a byproduct of amino acid metabolism and neurotransmitter turnover.
• Ammonia reacts with α-ketoglutarate and NADH to form glutamate, catalyzed by glutamate dehydrogenase.

α-ketoglutarate + NH₃​ ​+ NADH → Glutamate + NAD⁺ + H2​O

• Glutamate is converted to glutamine by glutamine synthetase, adding another ammonia molecule. Glutamine synthetase is predominantly found in astrocytes.

Glutamate + NH₃​ + ATP → Glutamine + ADP + Pi

• This conversion reduces ammonia toxicity by storing it in a non-toxic form.

Q8. A 2-year-old child is brought to the clinic by his parents due to darkening of the urine upon standing and brownish discoloration of the sclera and ear cartilage. The parents also report that the child has been experiencing joint pain. Upon further investigation, the physician suspects a tyrosine metabolic disorder related and orders urine tests Which of the following enzymes is most likely deficient in this patient?

1. Parahydroxy phenylpyruvate dioxygenase
2. Tyrosine transaminase
3. Homogentisate oxidase 
4. Fumarylacetoacetate hydrolase

Answer: 3) Homogentisate oxidase 

Explanation:
The clinical scenario described, including darkening of urine upon standing, brownish discoloration of the sclera and ear cartilage and joint pain is characteristic of alkaptonuria, which is caused by a deficiency in the enzyme homogentisate oxidase. 

Also read: Recombinant DNA Technology

Q.9 A 22-year-old woman presents with complaints of chronic fatigue and frequent infections. She follows a strict vegetarian diet and consumes less protein-rich food. Laboratory tests reveal a decreased level of a particular amino acid. Which of the following amino acids is likely deficient in this patient?

1. Threonine and Lysine
2. Tyrosine and Tryptophan
3. Alanine and Glycine
4. Cysteine and Methionine

Answer: 1) Threonine and Lysine

Q.10 Which of the following techniques is specifically designed to introduce specific genetic modifications, such as gene knock-ins or knock-outs, into the genome of an organism?

1. FISH (Fluorescence In Situ Hybridization)
2. CRISPR-Cas
3. Recombinant DNA Technology
4. Comparative Genomic Hybridization

Answer: 2) CRISPR-Cas

Explanation:

 CRISPR-Cas is a genome-editing tool that can be used to introduce specific genetic modifications, including gene knock-ins (adding new genetic material) and gene knock-outs (disrupting or deleting existing genes).

CRISPR-Cas Mechanism:

• Guide RNA: Directs the Cas enzyme to the specific DNA sequence.
• Cas Enzyme: Cuts the DNA at the target location.
• DNA Repair:
  • NHEJ (Non-Homologous End Joining): Repairs the break by directly ligating the DNA ends, often leading to gene knockout.
  • HDR (homologous directed repair): Uses a template to repair the break accurately, allowing for gene knock-in.

Q.11 Which of the following factors can cause the denaturation of DNA? 

a) Increasing temperature

b) Increasing salt concentration

c) Decreasing temperature

d) DNA with a high A-T base composition

e) DNA with a high G-C base composition

f) Adding Urea

g) Adding Formamide

h) Decreasing salt concentration

1. b,c,e,g,h
2. c,d,e,h
3. a,d,f,g,h
4. a,b,e,g

Answer: 3) a,d,f,g,h

Explanation:

Increasing temperature, decreasing salt concentration, DNA with a high A-T base composition, and Adding chaotropic agents like urea and formamide cause denaturation of DNA.

Also read: Properties of Genetic Code Mutation

Q.12 A 45-year-old patient diagnosed with COVID-19 has a real-time PCR test result showing a cycle threshold (Ct) value of 35. How should this Ct value be interpreted in the context of their infectivity and clinical management?

1. The patient has a high viral load and is highly infectious.
2. The patient has a low viral load and is less likely to be infectious.
3. The patient’s Ct value indicates they should be immediately admitted to the ICU.
4. The Ct value alone is sufficient to determine the patient’s disease severity and infectivity.

Answer: 2) The patient has a low viral load and is less likely to be infectious.

Explanation: Higher Ct values (>30) suggest a lower viral load, indicating reduced infectivity. 

Q.13 A 25-year-old student is reviewing the roles of small RNAs in cellular processes. She learns about small nuclear RNAs (snRNAs) and small interfering RNAs (siRNAs). Which of the following statements about snRNAs and/ or siRNAs is true?

1. Both snRNAs and siRNAs are involved in the degradation of mRNA.
2. snRNAs form complexes with the RNA-induced silencing complex (RISC).
3. snRNAs are primarily involved in mRNA splicing and are located in the nucleus.
4. snRNAs are typically found in the cytoplasm, while siRNAs are found in the nucleus.

Answer: 3) snRNAs are primarily involved in mRNA splicing and are located in the nucleus.

Explanation: 

Small nuclear RNAs (snRNAs) are essential components of the spliceosome, a complex responsible for removing introns from pre-mRNA (hnRNA) during splicing, which occurs in the nucleus.

Also read: Hartnup Disease and Glycine Metabolic Effects

Q.14 Which of the following statements accurately describes the changes in Km (Michaelis constant) and Vmax (maximum reaction rate) in the presence of an uncompetitive inhibitor?

1. Km increases, Vmax increases
2. Km decreases, Vmax decreases  
3. Km stays the same, Vmax decreases  
4. Km increases, Vmax stays the same

Answer: 2) Km decreases, Vmax decreases  

Explanation:

Uncompetitive Inhibition occurs when an inhibitor binds only to the enzyme-substrate complex, preventing it from converting the substrate into product. This type of inhibition results in:

• Decrease in Km: Since the inhibitor binds to the enzyme-substrate complex, it effectively lowers the concentration of the enzyme available for reaction, making the apparent affinity of the enzyme for the substrate appear higher.
• Decrease in Vmax: The inhibitor reduces the maximum rate of reaction because it prevents the enzyme-substrate complex from proceeding to form the product, thus lowering the overall reaction rate at saturating substrate concentrations. 

Therefore, in uncompetitive inhibition, both Km and Vmax decrease.

Q.15 A 45-year-old male presents with severe pain and swelling in his right calf following an intense workout session two days ago. Laboratory tests, including measurements of lactate dehydrogenase (LDH) isoenzymes, are ordered. Which LDH isoenzyme is most indicative of skeletal muscle pathology in this patient?

1. LDH-1
2. LDH-2
3. LDH-3
4. LDH-5

Answer: 4) LDH-5

Explanation:

LDH-5, primarily found in skeletal muscle and liver, serves as a biomarker and typically indicates skeletal muscle damage, seen in muscle injury, rhabdomyolysis, or intense physical exertion.

• Lactate dehydrogenase (LDH) is an enzyme involved in converting lactate to pyruvate during anaerobic glycolysis. 
• It consists of four subunits, forming five different isoenzymes that vary in tissue distribution. 

Also read: INI-CET High Yield Questions For Biochemistry

Q.16 Match the following disorders with the enzyme defects in context to relation synthesis.

Enzyme defect	Disorder
A) Uroporphyrinogen III synthase	i) Porphyria cutanea tarda
B) Uroporphyrinogen decarboxylase defect	ii) Congenital erythropoietic porphyria
C) ALA synthase II	iii) Acute intermittent porphyria
D) Porphobilinogen deaminase	iv) X-linked sideroblastic anemia

1. A-ii, B-i, C-iv, D-iii
2. A-iii, B-iv, C-ii, D-i
3. A-iv, B-iii, C-i, D-ii
4. A-i, B-ii, C-iv, D-iii

Answer: 1) A-ii, B-i, C-iv, D-iii

Explanation: 

Every defect in the enzyme involved in heme synthesis is associated with a disorder, as shown below:

Enzyme defect	Disorder
ALA synthase II	X-linked sideroblastic anemia
ALA dehydratase	ALA dehydratase deficiency porphyria
Porphobilinogen deaminase (Hydroxymethylbilane synthase)	Acute intermittent porphyria
Uroporphyrinogen III synthase	Congenital erythropoietic porphyria
Uroporphyrinogen decarboxylase	Porphyria cutanea tarda
Coproporphyrinogen oxidase	Hereditary coproporphyria
Protoporphyrinogen oxidase	Porphyria variegata
Ferro chelatase	Erythropoietic protoporphyria

Q.17 Identify the enzymes marked as a and b, in the flow chart as related to vitamin D synthesis.

1. α- 25 alpha hydroxylase, liver; β- 1 alpha hydroxylase, kidney  
2. α- 1 alpha hydroxylase, kidney ; β- 25 alpha hydroxylase, liver
3. α- 1 alpha hydroxylase, liver; β- 25 alpha hydroxylase, kidney 
4. α- 25 alpha-hydroxylase, kidney; β- 1 alpha-hydroxylase, liver

Answer: 1) α- 25 alpha hydroxylase, liver; β- 1 alpha hydroxylase, kidney  

Explanation:

Vitamin D synthesis:

(a: α- 25 alpha hydroxylase; b: β-1 alpha hydroxylase)

• Skin:
  • Most of the precursors for 1,25(OH)2-D3 synthesis are produced in the malpighian layer of the epidermis from 7-dehydrocholesterol via a UV light-mediated photolysis reaction. 
  • Conversion efficiency is affected by UV exposure and skin pigmentation. 
  • Aging reduces 7-dehydrocholesterol levels.
• Liver:
  • Vitamin D is transported to the liver by vitamin D-binding protein.
  • In the liver, vitamin D is hydroxylated to 25(OH)2-D3 (25 dihydroxy cholecalciferol) by 25 alpha-hydroxylase. 
  • This process requires magnesium, NADPH, molecular oxygen, and an uncharacterized cytoplasmic factor.
  • Two enzymes are involved: NADPH-dependent cytochrome P450 reductase and cytochrome P450.
  • 25(OH)2-D3 is the main circulating form of vitamin D and is transported to the kidney.
• Kidney:
  • 25(OH)D3 is converted to the active form, 1,25(OH)2D3 (1,25 dihydroxy cholecalciferol), in the kidneys by the enzyme 1 alpha-hydroxylase.
  • This conversion involves a three-component monooxygenase system requiring NADPH, magnesium, molecular oxygen, and three enzymes: renal ferredoxin reductase, renal ferredoxin, and cytochrome P450.
  • 1,25(OH)2D3 is the most potent active metabolite of vitamin D.

Also read: Mucopolysaccharides : Exceptions, Important Facts

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