Ask A Scientist© Molecular Biology Archive

name         Ayla L.
status       student
age          17

Question -   I actually have a few questions that i can just not
figure out here they are:
1.) Many biochemical reactions that occur in cells require relatively high
concentrations of potassium ion (k+).  The concentration of K+ in muscle
cells is about 0.15 M.  The concentration of K+ in blood plasma is about
0.0050 M.  The high internal concentration in cells is maintained by
pumping K+ fron plasma.  How much work must be done to transport 1.0 mol
of K+ from the blood to the inside of a muscle cell at 37C, normal body
temperature?  When 1.0 mol of K+ is transferred from blood to the cells,
do any other ions have to be transported? Why or why not? Much of the ATP
formed from metabolic processes is used in providing energy fro transport
of cellular componants.  How much ATP must be hydrolyzed to provide the
energy for the transport of 1.0 mol of K+?       For this equation i
couldn't even find the equation to figure out the work without knowing the
energy.... 
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The transport of potassium in animal cells is fairly well-understood. Animal
cells contain large, membrane-spanning protein complexes that actively
transport two different ions at the same time. The Na+ - K+ pump moves 3
sodium ions out of the cell for every 2 potassium ions that it transports in.
It is estimated that it requires the hydrolysis of 1 ATP molecule to ADP + Pi
for every 3 sodium/2 potassium ions moved. This transporter plays an
essential function in helping maintain the correct osmotic balance in the
cell by moving lots of sodium ions out of the cell. If you poison this
transporter with a chemical called ouabain, animal cells will swell and
burst. Just to give you an idea of how important this transporter is, it is
estimated that up to one third (!) of the energy required by an animal cell
is used to fuel this pump. (A good reference: Molecular Biology of the Cell,
Alberts et al.)

Paul Mahoney, Ph.D.
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