Question 1

Describe how tyrosine is degraded.

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Question 2

Explain why the amino acid tryptophan is both ketogenic and glucogenic.

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Question 3

Explain how tyrosinase deficiency causes albinism.

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Question 4

Why can't humans degrade purine rings?

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Question 5

The urea cycle occurs partially in the cytoplasm and partially in the mitochondrion. Discuss the urea cycle reactions with reference to these cellular locations.

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Question 6

In individuals with PKU, is tyrosine an essential amino acid?

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Question 7

Most amino acids are degraded in the liver. This is not true of the branch-chain amino acids, most of which degraded in extrahepatic tissues with high protein turnover. What is the primary tissue that uses branched chain amino acids?

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Question 8

Explain why providing domestic cats with a vegetarian diet is a bad idea.

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Question 9

Alkaptonuria, albinism, phenylketonuria are all examples of which kind of defiency?

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Question 10

Why can't humans simply excrete waste nitrogen atoms as ammonia rather than utilize the energetically expensive process of urea synthesis?

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Question 11

Phenylketonuria can be caused by deficiencies in phenylalanine hydroxylase and by enzymes catalyzing the formation and regeneration of 5,6,7,8,-tetrahydrobiopterin. How can this second deficit cause the symptoms of PKU?

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Question 12

In their in vitro studies using liver slices, Krebs and Henseleit observed that urea formation was stimulated by the addition of ornithine, citrulline, and arginine. Other amino acids had no effect. Explain these observations.

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Question 13

Caffeine, a methylated xanthine found in chocolate, coffee, and tea is excreted as uric acid. Use your knowledge of the metabolism of other purine compound to suggest how caffeine is metabolized.
  Caffeine

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Question 14

Discuss and compare the three forms of autophagy.

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Question 15

Urea formation is energetically expensive, requiring the expenditure of 4 mol of ATP per mole of urea formed. However NADH is produced when fumarate is reconverted to aspartate. How many ATP molecules are produced by the mitochondrial oxidation of the NADH? What is the net ATP requirement for urea synthesis?

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Quiz 15: Nitrogen Metabolism II: Degradation