20. How is the heme group held in the myoglobin molecule? What is the importance of heme to myoglobin's physiological role?
21. How does the amino acid sequence of myoglobin help the molecule to fold properly in three dimensions?
22. How does subunit interaction in hemoglobin affect the way that oxygen molecules bind to it?
23. What is a purine base? A pyrimidine base? Which purines and pyrimidines are used in DNA? What changes occur when DNA changes to RNA?
24. What is a nucleoside? A nucleotide? Give examples, when the base involved is adenine.
25. What structural elements are shared by AMP, NAD +, and FAD? What structural features distinguish NAD' and FAD from one another, and from ATP?
26. Why is NAD+ written with a + sign, whereas FAD is not? What happens to the hydrogen atoms when each of these dinucleotides is reduced? What is the standard abbreviation for the reduced form of each?
27. If molecular 0., is the final oxidant, how much free energy is carried by each mole of reduced NAD'? Of reduced FAD? Of ATP? What advantage is there in having several energy carriers with different capacities?
28. If NAD + is needed every time energy is extracted from foods, why do we require only minute quantities of niacin (a precursor of NAD1), instead of amounts comparable with our other foods?