Page 66 - Academic Press Encyclopedia of Physical Science and Technology 3rd BioChemistry

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Encyclopedia of Physical Science and Technology EN008K-353 June 29, 2001 12:41

Ion Transport Across

Biological Membranes

George P. Hess
Cornell University

I. Relationship Between Transmembrane V. Inorganic Ion Transport and the Rapid
Inorganic Ion Flux and Transmembrane Transmission of Electrical Signals over Long
Potential Distances (up to ∼1m)
II. Mechanism of Transmembrane Inorganic VI. Properties of the Protein (Potassium Channel)
+
+
Ion Flux that Allows K but Not Na to Cross
III. Inorganic Ion Transport and the Perception the Membrane
of Light VII. Inorganic Ion Transport against a Concentration
IV. Inorganic Ion Transport and Integration Gradient at Expense of ATP Hydrolysis
of Environmental Information VIII. Conclusion and Outlook

GLOSSARY tion and integration of, and reaction to, environmental sig-
nalsbytheorganism.Examplesincludevision,theintegra-
Adenosine triphosphate (ATP) Upon hydrolysis within tion and processing of this information (brain function),
a cell, ATP gives rise to adenosine diphosphate and and the reaction of the organism to this information, for in-
adenosinemonophosphatewith the liberationof energy stance, muscle contraction (Fig. 1). Cells have the ability
( G is about − 12 kcal/mol). to hydrolyze adenosine triphosphate (ATP). The energy
Faraday constant F Has a value of 96,485 coulombs per thus released is used to transport sodium and potassium
mole. ions across the cell membrane against a concentration gra-

Guanosine 3 ,5 -cyclic monophosphate (cGMP) Is con- dient. This process establishes the transmembrane voltage
verted to 5 guanosine monophosphate by an enzyme, (V m ) of the cell membrane. The transmembrane voltage

cGMP phosphodiesterase. is perturbed by the movement of inorganic ions (generally
−
+
Universal gas constant R Has a value of 8.314 joules Na ,K ,Cl , and Ca ) along the concentration gradient
2+
+
K −1 mol −1 (K is degrees Kelvin). and voltage difference across the cell membrane that oc-
curs in signal transmission between cells. There are many
different transmembrane channel-forming proteins, which
THE MOVEMENT of inorganic ions across biological are activated by (1) a concentration gradient of inorganic
membranes of animals plays a central role in the percep- ions across the membrane, (2) the transmembrane voltage,
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