Cellular Structure, Proteins, and Metabolism
Chapter 3 Quantitative and Thought Questions
(Answers appear in Appendix A.)
1. A base sequence in a portion of one strand of DNA is
a. the base sequence in the complementary strand of DNA.
b. the base sequence in RNA transcribed from the sequence
2. The triplet code in DNA for the amino acid histidine is
G—T—A. Predict the mRNA codon for this amino acid and
the tRNA anticodon.
3. If a protein contains 100 amino acids, how many nucleotides
will be present in the gene that codes for this protein?
4. A variety of chemical messengers that normally regulate
acid secretion in the stomach bind to proteins in the plasma
membranes of the acid-secreting cells. Some of these binding
reactions lead to increased acid secretion, others to decreased
secretion. In what ways might a drug that causes decreased acid
secretion be acting on these cells?
5. In one type of diabetes, the plasma concentration of the
hormone insulin is normal, but the response of the cells that
insulin usually binds to is markedly decreased. Suggest a reason
for this in terms of the properties of protein binding sites.
The following graph shows the relation between the
amount of acid secreted and the concentration of compound
X, which stimulates acid secretion in the stomach by binding
to a membrane protein. At a plasma concentration of 2 pM,
compound X produces an acid secretion of 20 mmol/h.
Acid secretion (mmol/h)
Plasma concentration of compound X (pM)
a. Specify two ways in which acid secretion by compound X
could be increased to 40 mmol/h.
b. Why will increasing the concentration of compound X to 28
pM fail to produce more acid secretion than increasing the
concentration of X to 18 pM?
7. In the following metabolic pathway, what is the rate of
formation of the end product E if substrate A is present at a
saturating concentration? The maximal rates (products formed
per second) of the individual steps are indicated.
8. If the concentration of oxygen in the blood delivered to a
muscle is increased, what effect will it have on the muscle’s rate
of ATP production?
9. During prolonged starvation, when glucose is not being
absorbed from the gastrointestinal tract, what molecules can be
used to synthesize new glucose?
10. Why do certain forms of liver disease produce an increase in the
blood levels of ammonia?