Concepts in Biochemistry, Chapter 19

1. N2 makes up about 80% of the atmosphere. This is the source of nitrogen for all living things. The nitrogen cycle describes the movement of N2 from the atmosphere to living things. Which of the following statements are true?
A.Bacteria reduce N2 to NH3.
B.Bacteria oxidize N2 to 2 NO3-.
C.All bacteria carry out nitrogen fixation.
D.NºN is highly reactive.


2. The nitrogenase complex converts N2 into NH4+ by the addition of electrons. Which of the following is NOT true of this complex?
A.It requires Fe-S protein.
B.Pyruvate is always the source of electrons.
C.It requires ATP.
D.It requires Mo-Fe protein.


3. Biosynthesis of Amino Acids Animal cells incorporate NH4+ into organic molecules. The addition of an NH4+ molecule to a ketoglutarate to produce glutamate requires:
A.NADH
B.NADP+
C.NADPH
D.NAD+
E.ATP
F.H2O


4. The addition of an NH4+ molecule to glutamate produces glutamine. This process requires:
A.NADPH
B.NADH
C.NADP+
D.NAD+
E.ATP
F.H2O


5. Which of the following statements about amino acid synthesis is NOT correct?
A.The carbon skeletons of amino acids come from glycolysis, citric acid, or phosphogluconate intermediates
B.All amino acids are derived from a common precursor.
C.The amino group is usually derived from glutamate.
D.Humans can only synthesize ten of the amino acids.


6. What is the role of tetrahydrofolate and S-adenosyl methione?
A.The transfer of electrons.
B.The transfer one-carbon units.
C.Both act as reductants.
D.Both act as oxidizers.
E.They are important in feedback inhibition.
F.They provide the "R" group for methionine.


7. The site of amino acid catabolism is the:
A.Stomach
B.Small intestine
C.Large intestine
D.Liver
E.Peripheral tissues


8. The first step in the catabolism of most amino acids is
A.Removal of carboxylate groups
B.Enzymatic hydrolysis of peptide bonds
C.Removal of the amino group
D.Zymogen cleavage
E.Catabolism of the carbon skeleton


9. Which of the following are true of amino acid catabolism?
A.Pyridoxal phosphate acts as an amino group carrier.
B.All amino acids are degraded into citric acid cycle intermediates.
C.Amino groups are transferred to arginine.
D.Pyridoxal phosphate transfers one-carbon units.


10. NH4+ is toxic to cells and must be eliminated. Vertebrates utilize the urea cycle to achieve this. Which of the following is NOT true of the urea cycle?
A.NH4+ elimination is a spontaneous process.
B.It requires ATP.
C.Both of the nitrogens on urea are derived from glutamate.
D.The synthesis of arginine is part of the urea cycle.


11. Many biomolecules are derived from amino acid precursors. Match the biomolecule with its precursor by entering the name of the correct precursor in the blank (choose from the following word bank). Glycine, Histidine, Glutamate, Tryptophan, Tyrosine, Arginine, Aspartate

_______________ à Serotonin

_______________ à Histamine

_______________ à Epinephrine

_______________ à g-aminobutyrate (GABA)

_______________ à Serotonin

_______________ à Heme

_______________ à Pyrimidines

_______________ à Nitric oxide

Answer:



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