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40. What enzyme deficiency causes orotic aciduria (without hyperammonemia)?
→ UMP synthase
39. What transcription factor binds hypoxia response elements?
→ HIF-1α (Hypoxia-Inducible Factor 1-alpha)
38. What enzyme converts dUMP to dTMP?
→ Thymidylate synthase
37. What is the inheritance pattern of Duchenne muscular dystrophy?
→ X-linked recessive
36. What condition is caused by defective LDL receptors?
→ Familial hypercholesterolemia
35. What process allows bacteria to exchange plasmid DNA through direct contact?
→ Conjugation
34. What molecule activates glycogen synthase?
→ Insulin
33. What enzyme is deficient in alkaptonuria?
→ Homogentisate oxidase
32. What enzyme catalyzes the rate-limiting step in cholesterol synthesis?
→ HMG-CoA reductase
31. What amino acid is used in the synthesis of serotonin?
→ Tryptophan
30. What cytokine is associated with cachexia?
→ TNF-alpha
29. What protein is defective in hereditary spherocytosis?
→ Spectrin (or ankyrin)
28. What enzyme activates trypsinogen to trypsin?
→ Enteropeptidase (enterokinase)
27. What protein binds iron in the blood?
→ Transferrin
26. What is the mechanism of action of allopurinol?
→ Xanthine oxidase inhibitor
25. What is the most abundant amino acid in collagen?
→ Glycine
24. What cell type is responsible for secreting IFN-γ?
→ Th1 cells
23. What enzyme converts norepinephrine to epinephrine?
→ Phenylethanolamine N-methyltransferase (PNMT)
22. What type of collagen is most abundant in bone?
→ Type I collagen
21. What enzyme is deficient in Tay-Sachs disease?
→ Hexosaminidase A
20. What is the rate-limiting enzyme of glycolysis?
→ Phosphofructokinase-1 (PFK-1)
19. What enzyme is deficient in Lesch-Nyhan syndrome?
→ Hypoxanthine-guanine phosphoribosyltransferase (HGPRT)
18. What vitamin is a cofactor for transaminases (aminotransferases)?
→ Vitamin B6 (pyridoxal phosphate)
17. What type of blot detects RNA?
→ Northern blot
16. Which protein regulates p53 by targeting it for degradation?
→ MDM2
15. What is the main activator of glycogen phosphorylase in muscle?
→ AMP (and calcium)
14. What enzyme converts pyruvate to oxaloacetate in gluconeogenesis?
→ Pyruvate carboxylase
13. What DNA repair process removes bulky thymine dimers?
→ Nucleotide excision repair
12. What amino acid is used to synthesize nitric oxide?
→ Arginine
11. What cofactor is required by pyruvate dehydrogenase and α-ketoglutarate dehydrogenase complexes?
→ Thiamine (Vitamin B1)
10. What enzyme is deficient in classic galactosemia?
→ Galactose-1-phosphate uridyltransferase (GALT)
9. What molecule allosterically activates PFK-1?
→ Fructose-2,6-bisphosphate
8. What DNA repair mechanism is defective in Lynch syndrome?
→ Mismatch repair
7. What vitamin deficiency leads to elevated methylmalonic acid and neurologic symptoms?
→ Vitamin B12 (cobalamin)
6. What enzyme is deficient in Von Gierke disease (GSD I)?
→ Glucose-6-phosphatase
5. What enzyme is deficient in McArdle disease (GSD V)?
→ Myophosphorylase (muscle glycogen phosphorylase)
4. Which enzyme initiates DNA replication by adding RNA primers?
→ Primase
3. What lab technique is used to amplify a specific DNA sequence in vitro?
→ Polymerase Chain Reaction (PCR)
2. Which G protein activates adenylate cyclase, increasing cAMP?
→ Gs (stimulatory)
1. What mitochondrial enzyme family controls intrinsic apoptosis by regulating cytochrome c release?
→ BCL-2 family
Simon Downes, MD, PhD 