Biochemistry Essentials: Deep Dive into High-Yield Concepts and PYQs

Integration of Metabolism

Q1. When there is a low insulin to glucagon ratio, which of the following enzymes is stimulated?

Answer: Hormone-sensitive lipase.

Q2. A diabetic patient presents with high VLDL. This is due to a combination of which of the following?

Answer: High activity of hormone-sensitive lipase and low activity of lipoprotein lipase.

Metabolic Fuels and ATP Generation

Q3. What is the metabolic fuel for RBCs during starvation?

Answer: Glucose.

Q4. Net ATP produced by complete oxidation of one molecule of glucose is?

Answer: 32 ATPs.

Inborn Errors of Metabolism: A Systematic Approach

Learning about inborn errors of metabolism (IEMs) can be simplified by asking four questions:

1. Which enzyme defect causes the condition?
2. Which pathway is this enzyme related to?
3. What is the significance of this pathway?
4. What are the cells for which this pathway is indispensable?

• Example: Tarui's Disease (Glycogen Storage Disorder Type VII)
  • Enzyme Defect: Phosphofructokinase-1.
  • Related Pathway: Glycolysis.
  • Significance: Glycolysis is the only pathway that generates ATP without oxygen.
  • Indispensable Cells: RBCs and white muscle fibers.
  • Clinical Features: Defects in glycolysis in RBCs lead to ATP pump failure, swelling, and rupture, causing hemolytic anemia. In white muscle fibers, it causes exercise intolerance, particularly to anaerobic exercises.

Electron Transport Chain (ETC) Inhibitors

Q6. Rotenone inhibits which complex?

Answer: Complex I (NADH dehydrogenase).

Glucose Transporters (GLUTs)

Q7. Which of the following glucose transporters is insulin sensitive?

1. GLUT1
2. GLUT2
3. GLUT3
4. GLUT4

Answer: GLUT4.

Glycogen Storage Disorders (GSDs)

Q8. A patient presents with cardiomegaly and floppy baby symptoms. What is your answer?

Answer: Pompe's disease.

Other Carbohydrate Disorders

Q9. A neonate with poor feeding, vomiting, acidosis, and cataract. Benedict's test positive on urine, but urinary glucose negative. Defective enzyme?

Answer: Galactose-1-phosphate uridyltransferase defect (Classical Galactosemia).

Q10. Congenital lactic acidosis is due to the defect of?

Answer: Pyruvate dehydrogenase complex.

Lipid Metabolism

Q11. Patients with xanthomas on Achilles tendon. Diagnosis?

Answer: Familial hypercholesterolemia (Type IIa).

Q12. Patient with severe abdominal pain (acute pancreatitis), serum triglyceride 2500 mg/dL. Suspected defect?

Answer: Apolipoprotein C-II (Apo C2) defect.

Q13. Patients with high triglyceride esterified with long-chain fatty acid, fatigue, and muscle biopsy shows fat vacuoles. Diagnosis?

Answer: Carnitine deficiency.

Glycosphingolipidoses (Lysosomal Storage Disorders)

Q14. A child presented with difficulty in vision. Cherry red spots were seen on the macula. There was no organogram. Identify the disease.

Answer: Tay-Sachs disease.

Q15. Refractory anemia and crumpled tissue paper appearance in bone marrow biopsy. Diagnosis?

Answer: Gaucher's disease.

Amino Acid Metabolism

Q16. Kidney pain and hexagonal crystals in the urine. Diagnosis?

Answer: Cystinuria (hexagonal crystals are cystine).

Q17. Phenylketonuria with normal phenylalanine hydroxylase levels. Deficiency?

Answer: Dihydrobiopterin reductase defect.

Q18. Probable causes of urine turning dark on standing?

Answer: Alkaptonuria.

Genetics

Q19. A 14-year-old boy, mentally retarded, complaining of joint pain, irresistible urge to bite his fingers and lips. Serum uric acid elevated. Diagnosis?

Answer: Lesch-Nyhan syndrome.

Q20. Which type of genetic abnormality can not be detected by FISH?

Answer: Point mutation 

Q21. What diagnostic method  is used in diagnosing aneuploidy?

Answer: FISH and Cytogenetics.

Q22. Following CRISPR-mediated gene editing, which of the following can result in gene knock-in?

1. non-homologous end joining repair
2. Homologous DNA Repair

Answer: Homologous DNA Repair.

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