Unit 6: Metabolism III - Practice Quiz

1 Which coenzyme is required for transamination reactions?

2 In a transamination reaction, an amino group is transferred from an amino acid to which common acceptor molecule?

3 The enzyme alanine aminotransferase (ALT) catalyzes the transfer of an amino group between alanine and which keto acid?

4 Which enzyme is primarily responsible for oxidative deamination of glutamate in the liver?

5 What is released as a product during the oxidative deamination of an amino acid?

6 Glutamate dehydrogenase can use which coenzyme(s) as electron acceptors?

7 Glucogenic amino acids are those that can be converted into which of the following?

8 Which of the following is a purely glucogenic amino acid?

9 Glucogenic amino acids typically enter metabolism by forming pyruvate or intermediates of which pathway?

10 Which two amino acids are exclusively ketogenic?

11 Ketogenic amino acids are degraded to acetyl-CoA or which other molecule?

12 The products of ketogenic amino acid degradation can be used to synthesize which of the following?

13 In which organ does the urea cycle primarily occur?

14 What is the main physiological significance of the urea cycle?

15 The urea cycle occurs partly in the mitochondria and partly in which cellular compartment?

16 How many nitrogen atoms does one molecule of urea contain?

17 In the de novo synthesis of purine nucleotides, the purine ring is built upon which starting molecule?

18 Which pathway reuses free purine and pyrimidine bases to form nucleotides?

19 In pyrimidine biosynthesis, the pyrimidine ring is first synthesized and then attached to ribose-5-phosphate. This differs from purine synthesis in which key way?

20 What is the final end product of purine degradation in humans?

21 During transamination, the amino group of an amino acid is transferred to -ketoglutarate, converting it into which product?

22 Which coenzyme is essential for the catalytic activity of aminotransferases (transaminases)?

23 Elevated serum levels of ALT (alanine aminotransferase) most specifically indicate damage to which organ?

24 Which enzyme catalyzes the oxidative deamination of glutamate, and what is a key product besides -ketoglutarate?

25 Glutamate dehydrogenase is an allosteric enzyme. Which molecule acts as an allosteric activator?

26 Why is the oxidative deamination of glutamate metabolically important for nitrogen disposal?

27 A glucogenic amino acid is one whose carbon skeleton can be converted into which intermediate for gluconeogenesis?

28 Which of the following amino acids is purely glucogenic?

29 During prolonged fasting, which glucogenic amino acid released from muscle is the major carrier of nitrogen to the liver for gluconeogenesis?

30 Which pair of amino acids is exclusively ketogenic?

31 Why can the carbon skeletons of purely ketogenic amino acids NOT be used for net glucose synthesis?

32 Which amino acids are considered both glucogenic and ketogenic?

33 In which two subcellular compartments do the reactions of the urea cycle occur?

34 Which enzyme catalyzes the committed, rate-limiting step of the urea cycle and requires N-acetylglutamate as an activator?

35 In the overall urea cycle, the two nitrogen atoms of urea are derived from which sources?

36 How many high-energy phosphate bonds (ATP equivalents) are consumed to synthesize one molecule of urea?

37 In de novo purine synthesis, the purine ring is assembled on which activated starting molecule?

38 Which key difference distinguishes de novo pyrimidine synthesis from purine synthesis?

39 The salvage pathway enzyme HGPRT, deficient in Lesch-Nyhan syndrome, is involved in the reuse of which molecules?

40 What is the final excretory product of purine degradation in humans?

41 During transamination, the pyridoxal phosphate (PLP) cofactor forms a covalent intermediate with the amino acid substrate. Which intermediate is the immediate species formed before the ketimine, and what is its significance?

42 A clinician measures elevated serum ALT (alanine aminotransferase). Which reaction does ALT catalyze, and why is it a useful marker?

43 Glutamate dehydrogenase (GDH) occupies a central role because it channels nitrogen from transamination into free ammonia. Which statement about its regulation is correct?

44 Why is glutamate uniquely positioned to undergo oxidative deamination while most other amino acids are not directly deaminated this way?

45 An amino acid is catabolized to succinyl-CoA. Explain why this makes it glucogenic despite succinyl-CoA being a TCA intermediate.

46 Which set contains amino acids that are exclusively glucogenic (neither ketogenic nor both)?

47 Leucine and lysine are the only two purely ketogenic amino acids. What is the metabolic consequence of this classification during prolonged starvation?

48 Isoleucine is classified as both glucogenic and ketogenic. Which pair of end products justifies this dual classification?

49 In the urea cycle, the two nitrogen atoms of urea originate from distinct sources. Identify them correctly.

50 Carbamoyl phosphate synthetase I (CPS-I) requires an allosteric activator. What is it, and what does its requirement signify metabolically?

51 A newborn presents with hyperammonemia, elevated orotic acid in urine, and low citrulline. Which enzyme deficiency best explains this pattern?

52 How many high-energy phosphate bonds (ATP equivalents) are consumed to synthesize one molecule of urea, and why?

53 In de novo purine synthesis, the purine ring is built directly on ribose-5-phosphate. Which is the true committed and rate-limiting step of the pathway?

54 The conversion of IMP to AMP and GMP is reciprocally regulated by energy status. Which statement is correct?

55 Ribonucleotide reductase converts ribonucleotides to deoxyribonucleotides. Which reductant ultimately supplies the electrons, and what regenerates it?

56 In de novo pyrimidine synthesis, the ring is assembled first and then attached to ribose. Which reaction supplies the sugar-phosphate, and at what stage?

57 A patient with gout has hyperuricemia. Which enzyme's activity most directly produces uric acid, and what reaction does it catalyze?

58 Lesch-Nyhan syndrome results from HGPRT deficiency. Why does loss of a salvage enzyme paradoxically cause overproduction of uric acid?

59 Adenosine deaminase (ADA) deficiency causes severe combined immunodeficiency (SCID). What is the biochemical mechanism linking ADA loss to lymphocyte toxicity?

60 Compared to purines, the degradation of pyrimidines yields highly soluble products. Which set represents typical pyrimidine catabolic end products?