General Chemistry Principles, Patterns, and Applications, 2011

histidine, the nine enzymes needed to synthesize histidine would all be active. If the cell had adequate
histidine, however, those enzymes would be inactive. The following diagram illustrates a situation in which
three amino acids (D, F, H) are all synthesized from a common species, A. The numbers above the arrows
refer to the enzymes that catalyze each step. Which enzymes would need to be regulated to produce D? F?
H?
♦ 16.
Because phosphorus-32 is incorporated into deoxyribonucleic acid (DNA), it can be used to
detect DNA fragments. Consequently, it is used extensively in biological research, including
the Human Genome Project, whose goal was to determine the complete sequence of
human DNA. If you were to start with a 20 g sample of phosphorus that contained 10% 32 P
by mass, converted it into DNA via several chemical steps that had an overall yield of 75%
and took 25 days, and then incorporated it into bacteria and allowed them to grow for 5
more days, what mass of 32 P would be available for analysis at the end of this time?
17. The enzyme urease contains two atoms of nickel and catalyzes the hydrolysis of urea by the following
reaction:
H 2 NC(O)NH 2 + H 2 O → 2NH 3 + CO 2
Urease is one of the most powerful catalysts known. It lowers the activation energy for the hydrolysis of urea
from 137 kJ/mol to only 37 kJ/mol. Calculate the ratio of the reaction rate of the catalyzed reaction to the
reaction rate of the uncatalyzed reaction at 37°C. Assume that the frequency factor is the same for both
reactions.
16. As noted in Section 14.8 "Catalysis", the reaction rate for the hydrogenation of ethylene to give ethane can
be increased by heterogeneous catalysts such as Pt or Ni:
H2 g
( ) + H2C = CH 2 g
( )- ® -Pt,NiH 3C – CH 3 g
The activation energy for the uncatalyzed reaction is large (188 kJ/mol), so the reaction is very slow at room
temperature. In the presence of finely divided metallic Ni, the activation energy is only 84 kJ/mol. Calculate
( )
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