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Problem 19.17
Does the enzyme described in each of the following statements require a cofactor to be active?
c. The presence of K⁺ does not affect the reaction.
Problem 19.18
Which vitamin provides us with each of the following?
b. Coenzyme A
Problem 19.21
Vitamins are a diverse group of compounds that must be present in the diet. List four functions of vitamins in the body.
Problem 19.3
The cofactors NAD+, Cu2+, Zn2+, coenzyme A, FAD, and Ni2+ are all needed by your body for enzymatic reactions.
a. Which cofactors are coenzymes?
Problem 19.32
Name the vitamin to which each of these coenzymes is related.
b. Coenzyme A
Problem 19.33
Which of the following is a cofactor and which is a coenzyme?
a. Cu2+
Problem 19.33
Which of the following is a cofactor and which is a coenzyme?
b. Tetrahydrofolate
Problem 19.33
Which of the following is a cofactor and which is a coenzyme?
c. NAD+
Problem 19.35
Which of the following is a cofactor and which is a coenzyme?
a. Fe2+
Problem 19.35
Which of the following is a cofactor and which is a coenzyme?
b. Pyridoxyl phosphate
Problem 19.74
What criteria make a compound a vitamin?
Problem 19.75
What is the relationship between vitamins and enzymes?
Problem 19.76
Why is daily ingestion of vitamin C more critical than daily ingestion of vitamin A?
Problem 19.78
Why is it important that the macronutrients calcium and phosphorus be ingested in approximately equal amounts?
Problem 19.8
Look up the structures of vitamin C and vitamin E on the Web, and identify the functional groups in these vitamins.
Problem 19.81
What is the relationship between vitamin A and β-carotene? (Hint: Look up the structures on the Web.)
Problem 21.19
The reduced coenzymes NADH and FADH₂ are oxidized in the ETS. What is the final electron acceptor of the ETS? What is the function of the H⁺ ion in ATP synthesis?
Problem 21.2
The overall equation in this section,
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shows the cycle between photosynthesis and oxidation. Pathways operating in opposite directions cannot be exergonic in both directions.
a. Which of the two pathways in this cycle is exergonic and which is endergonic?
Problem 21.21
Each of these reactions is involved in one of the four stages of metabolism shown in Figure 21.4. Identify the stage in which each reaction occurs.
a. Hydrolysis of starch to produce glucose
Problem 21.21
Each of these reactions is involved in one of the four stages of metabolism shown in Figure 21.4. Identify the stage in which each reaction occurs.
b. Oxidation of NADH coupled with synthesis of ATP
Problem 21.21
Each of these reactions is involved in one of the four stages of metabolism shown in Figure 21.4. Identify the stage in which each reaction occurs.
c. Conversion of glucose to acetyl-CoA
Problem 21.22
For the first step in fatty acid catabolism, we say that ATP is used to “drive” the reaction that links the fatty acid with coenzyme-A. Without ATP hydrolysis, would you predict that the linking of fatty acid to coenzyme-A would be exergonic or endergonic? In fatty acid CoA synthesis, the hydrolysis of the ATP portion is based on what major strategy of metabolism?
Problem 21.23
Since no molecular oxygen participates in the citric acid cycle, the steps in which acetyl groups are oxidized to CO₂ involve removal of hydride ions and hydrogen ions. What is the acceptor of hydride ions? What is the acceptor of hydrogen ions?
Problem 21.24
The reaction that follows is catalyzed by isocitrate dehydrogenase and occurs in two steps, the first of which (step A) is formation of an unstable intermediates (shown in brackets).
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a. In which step is a coenzyme needed? Identify the coenzyme.
Problem 21.24
The reaction that follows is catalyzed by isocitrate dehydrogenase and occurs in two steps, the first of which (step A) is formation of an unstable intermediates (shown in brackets).
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b. In which step is CO₂ evolved and a hydrogen ion added?
Problem 21.26
The electron-transport chain uses several different metal ions, especially iron, copper, zinc, and manganese. Why are metals used frequently in these two pathways? What can metals do better than organic biomolecules?
Problem 21.29
Why is ∆G a useful quantity for predicting the favorability of biochemical reactions?
Problem 21.31
The following reactions occur during the catabolism of acetyl-CoA. Which are exergonic? Which is endergonic? Which reaction produces a phosphate that later yields energy by giving up a phosphate group?
c. L-Malate + NAD+ → Oxaloacetate + NADH + H+
∆G = +17 kcal/mol (+129.3 kJ/mol)
Problem 21.32
The following reactions occur during the catabolism of glucose. Which are exergonic? Which is endergonic? Which proceeds farthest toward products at equilibrium?
b. Phosphoenol pyruvate + H2O → Pyruvate + Phosphate(Pi)
∆G = ―14.8 kcal/mol (―61.9 kJ/mol)
Problem 21.39
What is the difference between catabolism and anabolism?
