Chemistry of Uptake—Thermodynamic and Kinetic Factors in Passive Transport

  • Ei-Ichiro Ochiai
Part of the Biochemistry of the Elements book series (BOTE, volume 7)


“Uptake” is used in a more general sense than simply absorption. It is taken to include such phenomena as the incorporation of a specific metal ion into a specific biological functional unit (such as chlorophyll or an enzyme), in addition to transport across a membrane (absorption). The problem of uptake of elements has many facets. Absorption entails the movement of molecules from one location to another across a boundary. The boundary can be a cell membrane; a membrane of a cytoplasmic organelle such as the mitochondrion, chloroplast, or nucleus; or a combination of a cell wall and a cell membrane. Some of the major aspects of absorption are illustrated in Fig. 8–1. There are two classes of transmembrane movement of a substance, whether it be a proton, a metal cation, a metal complex, an anion, or a neutral molecule. One class is known as “active” transport and the other as “passive.” In passive transport, a substance moves along an electrochemical potential gradient; the motion occurs spontaneously without any added expenditure of energy. In active transport, a substance is forced to move against an electrochemical potential gradient; thus, the process requires an input of some sort of energy. In most cases this energy comes from the hydrolysis of ATP. A membrane-bound protein seems to be involved in this kind of transport. In other instances of active transport, the transmembranous movement of a substance is coupled with a second process of material transport that itself may or may not be active.


Passive Transport Mucosal Membrane Anion Binding Electrochemical Potential Gradient Transmembranous Movement 
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Copyright information

© Plenum Press, New York 1987

Authors and Affiliations

  • Ei-Ichiro Ochiai
    • 1
  1. 1.Juniata CollegeHuntingdonUSA

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