Essential Cell Biology 5th edition

Questions
453
QUESTION 13–13
An animal cell, roughly cubical in shape with a side length
of 10 μm, uses 10 9 ATP molecules every minute. Assume
that the cell replaces this ATP by the oxidation of glucose
according to the overall reaction 6O 2 + C 6 H 12 O 6 →
6CO 2 + 6H 2 O and that complete oxidation of each glucose
molecule produces 30 ATP molecules. How much oxygen
does the cell consume every minute? How long will it take
before the cell has used up an amount of oxygen gas equal
to its own volume? (Recall that one mole of a gas has a
volume of 22.4 liters.)
QUESTION 13–14
Under the conditions existing in the cell, the free energies
of the first few reactions in glycolysis (in Panel 13–1,
pp. 436–437) are:
step 1 ΔG = –33.5 kJ/mole
step 2 ΔG = –2.5 kJ/mole
step 3 ΔG = –22.2 kJ/mole
step 4 ΔG = –1.3 kJ/mole
Are these reactions energetically favorable? Using these
values, draw to scale an energy diagram (A) for the overall
reaction and (B) for the pathway composed of the four
individual reactions.
QUESTION 13–15
The chemistry of most metabolic reactions was deciphered
by synthesizing metabolites containing atoms that are
different isotopes from those occurring naturally. The
products of reactions starting with isotopically labeled
metabolites can be analyzed to determine precisely which
atoms in the products are derived from which atoms in
the starting material. The methods of detection exploit,
for example, the fact that different isotopes have different
masses that can be distinguished using biophysical
techniques such as mass spectrometry. Moreover, some
isotopes are radioactive and can therefore be readily
recognized with electronic counters or photographic film
that becomes exposed by radiation.
A. Assume that pyruvate containing radioactive 14 C
in its carboxyl group is added to a cell extract that can
support oxidative phosphorylation. Which of the molecules
produced should contain the vast majority of the 14 C that
was added?
B. Assume that oxaloacetate containing radioactive 14 C in
its keto group (refer to Panel 13–2, pp. 442–443) is added
to the extract. Where should the 14 C atom be located after
precisely one turn of the citric acid cycle?
QUESTION 13–16
In cells that can proliferate both aerobically and
anaerobically, fermentation is inhibited in the presence of
O 2 . Suggest a reason for this observation.