Essential Cell Biology 5th edition

Questions
425
QUESTION 12–18
Amino acids are taken up by animal cells using a symport
in the plasma membrane. What is the most likely ion
whose electrochemical gradient drives the import? Is ATP
consumed in the process? If so, how?
QUESTION 12–19
We will see in Chapter 15 that endosomes, which are
membrane-enclosed intracellular organelles, need an acidic
lumen in order to function. Acidification is achieved by an
H + pump in the endosomal membrane, which also contains
Cl – channels. If the channels do not function properly (e.g.,
because of a mutation in the genes encoding the channel
proteins), acidification is also impaired.
A. Can you explain how Cl – channels might help
acidification?
B. According to your explanation, would the Cl – channels
be absolutely required to lower the pH inside the
endosome?
QUESTION 12–21
Acetylcholine-gated cation channels do not discriminate
between Na + , K + , and Ca 2+ ions, allowing all to pass
through them freely. So why is it that when acetylcholine
binds to this protein in the plasma membrane of muscle
cells, the channel opens and there is a large net influx of
primarily Na + ions?
QUESTION 12–22
The ion channels that are regulated by binding of
neurotransmitters, such as acetylcholine, glutamate, GABA,
or glycine, have a similar overall structure. Yet each class
of these channels consists of a very diverse set of subtypes
with different transmitter affinities, different channel
conductances, and different rates of opening and closing.
Do you suppose that such extreme diversity is a good or
a bad thing from the standpoint of the pharmaceutical
industry?
QUESTION 12–20
Some bacterial cells can grow on either ethanol
(CH 3 CH 2 OH) or acetate (CH 3 COO – ) as their only carbon
source. Dr. Schwips measured the rate at which the two
compounds traverse the bacterial plasma membrane but,
due to excessive inhalation of one of the compounds (which
one?), failed to label his data accurately.
A. Plot the data from the table below.
Concentration of
Carbon Source (mM)
Rate of Transport (μmol/min)
Compound A
Compound B
0.1 2.0 18
0.3 6.0 46
1.0 20 100
3.0 60 150
10.0 200 182
B. Determine from your graph whether the data describing
compound A correspond to the uptake of ethanol or
acetate.
Explain your answers.