MBBS Biochemistry 2 — Questions and Answers
Question 1: Gaucher disease results from deficiency of which enzyme?
- Sphingomyelinase
- Glucocerebrosidase (beta-glucosidase) (Correct answer)
- Hexosaminidase A
- Alpha-galactosidase A
Correct answer: Glucocerebrosidase (beta-glucosidase)
Gaucher disease is the most common lysosomal storage disorder, caused by glucocerebrosidase deficiency, leading to glucocerebroside accumulation in macrophages.
Question 2: Which of the following is the primary product of the pentose phosphate pathway?
- ATP and pyruvate
- NADPH and ribose-5-phosphate (Correct answer)
- Acetyl-CoA and NADH
- Oxaloacetate and FADH2
Correct answer: NADPH and ribose-5-phosphate
The pentose phosphate pathway generates NADPH (for reductive biosynthesis and antioxidant defense) and ribose-5-phosphate (for nucleotide synthesis).
Question 3: The DNA double helix is held together by which type of bonds between base pairs?
- Covalent bonds
- Ionic bonds
- Hydrogen bonds (Correct answer)
- Disulfide bonds
Correct answer: Hydrogen bonds
Complementary base pairs (A-T and G-C) in DNA are held together by hydrogen bonds; G-C pairs have 3 hydrogen bonds and A-T pairs have 2.
Question 4: Which lipoprotein is responsible for transporting cholesterol from peripheral tissues to the liver (reverse cholesterol transport)?
- Chylomicrons
- VLDL
- LDL
- HDL (Correct answer)
Correct answer: HDL
HDL mediates reverse cholesterol transport, collecting cholesterol from peripheral tissues and transporting it to the liver for excretion.
Question 5: Vitamin B12 deficiency causes megaloblastic anemia through impaired synthesis of which molecule?
- Heme
- Globin chains
- Thymidine (dTMP) (Correct answer)
- Ferritin
Correct answer: Thymidine (dTMP)
B12 deficiency impairs methionine synthesis, trapping folate as methyl-THF and preventing thymidine synthesis, impairing DNA replication and causing megaloblastic anemia.
Question 6: Which enzyme converts fibrinogen to fibrin in the coagulation cascade?
- Factor X
- Prothrombin
- Thrombin (Correct answer)
- Plasmin
Correct answer: Thrombin
Thrombin (activated from prothrombin by Factor Xa/Va) cleaves fibrinopeptides A and B from fibrinogen, generating fibrin monomers that polymerize into a clot.
MBBS Biochemistry 2
Gaucher disease results from deficiency of which enzyme?