Critical Thinking Questions

1. Because enzymes are proteins, they can denature. How does this explain the fact that changes in the pH of body fluids during illness may threaten life?

2. Some weight-reducing diets drastically limit intake of carbohydrates but allow many foods rich in fat and protein. What changes would such a diet cause in cellular metabolism? How would excretion of substances from the internal environment change?

3. Why are vitamins that function as coenzymes in cells required in extremely low concentrations?

4. What changes in concentrations of oxygen and carbon dioxide would you expect to find in the blood of a person who is forced to exercise on a treadmill beyond his or her normal capacity? How might these changes affect the pH of the person's blood?

5. How do the antibiotic actions of penicillin and streptomycin differ?

6. A student is accustomed to running three miles each afternoon at a slow, leisurely pace. One day, she runs a mile as fast as she can. Afterwards she is winded, with pains in her chest and leg muscles. She thought she was in great shape! What has she experienced, in terms of energy metabolism?

7. In fructose intolerance, a missing enzyme makes a person unable to utilize fructose, a simple sugar abundant in fruit. Infants with the condition have very low mental and motor function. Older children are very lethargic and mildly mentally retarded. By adulthood, the nervous system deteriorates, eventually causing mental illness and death. Molecules that are derived from fructose are intermediates in the first few reactions of glycolysis. The enzyme missing in people with fructose intolerance would normally catalyze these reactions. Considering this information about the whole-body and biochemical effects of fructose intolerance, suggest what might be happening on a cellular level to these people.

8. Write the sequence of the complementary strand of DNA to the sequence A, G, C, G, A, T, T, G, C, A, T, G, C. What is the sequence of mRNA that would be transcribed from the given sequence?

9. Explain why exposure to ultraviolet light in tanning booths may be dangerous.

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