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Problem 22.34
What are the products of digestion of proteins, triacylglycerols, maltose, sucrose, lactose, and starch?
Problem 24.14
Three metabolites that can result from the breakdown of the carbon skeleton of amino acids are ketone bodies, acetyl-CoA, and glucose. Briefly describe how each of these metabolites can be produced from amino acid catabolism.
Problem 24.41
Which of the following biomolecules contain nitrogen?
a. Glycogen (Chapter 22)
b. Nitric oxide (Chapter 4)
c. Collagen (Chapter 18)
d. Epinephrine (Chapter 28)
e. Stearic acid (Chapter 23)
f. Fructose (Chapter 20)
Problem 25.1
Decide whether each of the following statements is true or false. If false, explain why.
a. The amino acid pool is found mainly in the liver.
Problem 25.15
Define what an “essential” nutrient is and explain how it differs from a “nonessential” nutrient.
Problem 25.2
What citric acid cycle intermediates are precursors to amino acids?
Problem 25.23
What is the structure of the α-keto acid formed from transamination of the following amino acids?
a. Glutamic acid
Problem 25.27
Write the structure of the α-keto acid produced by oxidative deamination of the following amino acids (Refer to Table 18.3):
a. Leucine
Problem 25.28
What other product is formed in oxidative deamination besides an α-keto acid?
Problem 25.3
What is the structure of the α-keto acid formed by transamination of the amino acid phenylalanine (Phe)? Refer to Table 18.3 for the structure of Phe.
Problem 25.31
Why does the body convert NH₄⁺ to urea for excretion?
Problem 25.37
If you were diagnosed as having a diet low in lysine, what foods might you include in your diet to alleviate this problem?
Problem 25.4
Diet soft drinks that are sweetened with aspartame carry a warning label for phenylketonurics. Why?
Problem 25.44
a. Name the four compounds within the citric acid cycle that the carbon skeletons of the glucogenic amino acid enter as.
Problem 25.45
Can an amino acid be both glucogenic and ketogenic? Explain why or why not.
Problem 25.5
The pancreatic proteases are synthesized and stored as zymogens. They are activated after the pancreatic juices enter the small intestine. Why is it essential that these enzymes be synthesized and stored in their inactive forms?
Problem 25.6
Unlike most amino acids, branched-chain amino acids are broken down in tissues other than the liver. Using Table 18.3, identify the three amino acids with branched-chain R groups. For any one of these amino acids, write the equation for its transamination.
Problem 258
Fumarate from step 3 of the urea cycle may be recycled into aspartate for use in step 2 of the cycle. The sequence of reactions for this process is
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Classify each reaction as one of the following:
1. Oxidation
2. Reduction
3. Transamination
4. Elimination
5. Addition
Problem 2516
In the liver, the relative activity of ornithine transcarbamylase is high, that of argininosuccinate synthetase is low, and that of arginase is high. Why is it important that ornithine transcarbamylase activity be high in the liver? What might be the consequence if arginase activity is low or defective?
Problem 2533
From what two amino acids do the nitrogens in urea arise? (Hint: See Figure 25.3.)
Problem 2552
The net reaction for the urea cycle shows that three ATPs are hydrolyzed; however, the total energy “cost” is four ATPs. Explain why this is true.
