Ion Transport Across Biological Membranes

Important Terms (Ion Transport Across Biological Membranes)

Adenosine triphosphate (ATP) Upon hydrolysis within a cell, ATP gives rise to adenosine diphosphate and adenosine monophosphate with the liberation of energy (AG is about – 12 kcal/mol). Faraday constant F Has a value of 96,485 coulombs per mole. Guanosine 3 ,5 -cyclic monophosphate (cGMP) Is converted to 5′ guanosine monophosphate by an enzyme, cGMP […]

THE MOVEMENT (Ion Transport Across Biological Membranes)

THE MOVEMENT of inorganic ions across biological membranes of animals plays a central role in the perception and integration of, and reaction to, environmental signals by the organism. Examples include vision, the integration and processing of this information (brain function), and the reaction of the organism to this information, for instance, muscle contraction (Fig. 1). […]

RELATIONSHIP BETWEEN TRANSMEMBRANE INORGANIC ION FLUX AND TRANSMEMBRANE POTENTIAL

Membranes surround the individual cells of animals and organelles within the cell. They are composed of lipids and proteins. Specific proteins are responsible for the transport of specific inorganic ions across the membrane. Invariably, this transport of inorganic ions across the cell membrane is accompanied by changes in the transmembrane voltage. The equilibrium transmembrane potential […]

MECHANISM OF TRANSMEMBRANE INORGANIC ION FLUX

Here, the emphasis is on kinetic techniques used to obtain the information needed to understand the mechanism of protein-mediated reactions that allow the transport of inorganic ions across biological membranes. A combination of structural, thermodynamic, and kinetic information is required to achieve this understanding. The use of X-ray crystallography, NMR measurements, and electron microscopy, to […]

INORGANIC ION TRANSPORT AND THE PERCEPTION OF LIGHT

We shall now follow a cascade that consists of the perception of an environmental signal, the movement of ions across membranes and the resulting changes in transmem-brane voltage, and the reaction of the organism to the signal (Fig. 1). Because we know most about the sensory cells of the eye, this system is used as […]

INORGANIC ION TRANSPORT AND INTEGRATION OF ENVIRONMENTAL INFORMATION

In the previous section, the transport of ions across the membrane was initiated by an environmental signal, namely, light. This resulted in a change in the transmem-brane voltage and a subsequent influx of calcium ions into the nerve terminal of a sensory cell (Fig. 1), resulting in the release of a chemical signal. In general, […]

INORGANIC ION TRANSPORT AND THE RAPID TRANSMISSION OF ELECTRICAL SIGNALS OVER LONG DISTANCES (UP TO m)

The movement of inorganic ions across a cell membrane that initiates an electrical signal is only one step in signal transmission in organisms. The rapid transmission of this signal, over distances of up to 1 m, by the axon of cells is discussed next. How is the signal that was initiated by neurotransmitter-mediated reactions propagated? […]

PROPERTIES OF THE PROTEIN (POTASSIUM CHANNEL) THAT ALLOWS K+ BUT NOT Na+ TO CROSS THE MEMBRANE (Ion Transport Across Biological Membranes)

Recently, we have learned some of the properties of one channel that plays a central role in rapid signal transmission. The K+ channel from bacteria was crystallized, after a cytoplasmic tail of 33 residues was removed, and MacKinnon and colleagues have determined its structure at a resolution of 3.2 A (Fig. 7). This work represents […]

INORGANIC ION TRANSPORT AGAINST A CONCENTRATION GRADIENT AT EXPENSE OF ATP HYDROLYSIS

Most cells have a high concentration of K+ and a low concentration of Na+ inside the cell membrane relative to the concentration of these ions bathing the cell. As discussed, the rapid flow of these ions along their concentration gradient across the cell membrane is used in signal transduction between the cells of an organism, […]

CONCLUSION AND OUTLOOK (Ion Transport Across Biological Membranes)

It should be mentioned that examples of two types of ion channels have been given. (1) So-called slow channels involve second messengers. The examples given here are the light-activated channels that are opened by cGMP and the transmembrane membrane ion transport that requires the hydrolysis of ATP. (2) Fast activated channels. For activation, these just […]