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Reading Guide, Pratt and Cornely Chapter 18
1. What is meant by “fixed” nitrogen? How is it fixed? Is it an energetically costly process?
2. What is the reaction catalyzed by glutamine synthetase? What is the role of glutamine
synthetase in humans? What is its role in bacteria?
3. How is nitrogen transferred from one amino acid to another? What is the necessary cofactor?
4. What compound is made when these compounds are transaminated: alanine, glutamate,
aspartate.
5. Which amino acid is used as the backbone of arginine and histidine?
6. Give a three step synthesis of 3-phosphoglycerate to serine.
7. When serine donates a methylene group to the vitamin ____________, the amino acid
______________ is formed.
8. Which amino acid is the precursor for each of these neurotransmitters: GABA, dopamine,
serotonin.
Skip biosynthesis of essential amino acids and nucloetodes (questions 9-17 below aren’t
covered this semester.)
9. Purine bases are synthesize right onto the molecule ____________________.
10. Five substrates are used in a complex path to produce ___________________, which is the
precursor of AMP and GMP.
11. Describe a mechanism for balancing the production of AMP and GMP synthesis from IMP
12. In contrast to purine synthesis, pyrimidines bases are first ___________ subsequently
_______________________________.
13. Explain how the production of UTP and CTP differ from the branched pathway that forms
AMP and GMP.
14. What reaction is catalyzed by ribonucleotide reductase? Draw the structure of its unusually
stable free radical.
15. What is the ultimate reducing agent for transformation of NDP to dNDP?
16. What is a salvage pathway?
17. Contrast the catabolic fates of purines and pyrimidines.
18. What reaction is catalyzed by thymidylate synthase? What reaction is catalyzed by
dihydrofolate reductase? Why are these good targets for chemotherapy?
19. Amino acids are not completely catabolized in the liver. Rather, the nitrogen is removed
through ________________ reactions, then the carbon skeletons are transformed into
compounds such as ____________ and ____________ for fuel storage..
20. Two catabolic classifications for amino acids are ____________ and ______________.
21. List 5 amino acids that can be made into citric acid cycle intermediates by transamination or
deamination.
22. Serine can be made into the intermediate _____________ by deamination.
23. The four amino acids _______________ are part of the glutamate family, and make up 25%
of amino acid dietary intake.
24. Threonine is both ketogenic and glucogenic because it can be broken down into
____________ and _____________.
25. Glycine can be broken down by the glycine cleavage system to give a methylene group to the
vitamin ____________________.
26. Branched amino acids that are glucogenic yield ______________; branched amino acids that
are ketogenic yield _______________.
27. Aromatic amino acids are both keto- and glucogenic because they are broken down into
___________________ and either ______________ or _______________.
28. Why is excess nitrogen from metabolic processes not simply excreted as ammonia?
29. What is glutamate’s particular role in nitrogen elimination? What is the reaction catalyzed by
glutamate dehydrogenase?
30. How many ATP are consumed in the production of carbamoyl phosphate from carbonate?
Outline the three reactions necessary to produce this carbamoyl phosphate.
31. The urea cycle incorporates a nitrogen atom from carbamoyl phosphate and a nitrogen atom
from the amino acid _______________ to make the amino acid ________________ (which is an
essential amino acid in children.) The amino acid loses the molecule ___________ through
hydrolysis, which is excreted in the urine.
32. The total ATP cost of the urea cycle is __________, with a cost of ____ATP to make
carbamoyl phosphate, and a cost of _____ ATP to incorporate the aspartate nitrogen atom.
33. The regulated step of the urea cycle is ______________. It is activated by N-acetylglutamate,
which makes sense because N-acetylglutamate is made when _____________ and
_______________ are in high concentrations (a signal that amino acids are being catabolized.)