Energized Ion Exchange

There are two major sources of energy open to cells. One is a gradient of protons, H+ (a pH gradient), developed from the action of light of from the oxidation of organic molecules (Figure 5), while the second comes from the hydrolysis of pyrophosphate bound to nucleotides such as adenosine triphosphate (ATP). The proton gradient can be used in direct ion exchange with other ions, X, across the membrane to accumulate them:

Table 4 Examples of ATP-driven ion exchange pumps in cell membranes

Pump

Function

K + moves in; Na + moves out. Nerve conduction Ca2+ moves out. Fast (skeletal) muscle recovery Trace element input or rejection

The use of ATP is that its hydrolysis energy (— AG) can pump ions across membranes:

' Xin or to develop unfavourable gradients for protection by removing X or M from the cell to the environment:

It is now known that the action of ATP pumps frequently involves ion exchange so that transfer of one cation or anion is coupled to transfer of a second ion in the opposite direction, giving ion exchange while building energized ion gradients. Examples are given in Table 4.

The first is termed a symport and the second an antiport. In every case, movement across the membrane can be aided by carriers, M or X in the membrane, or by utilizing channels. Channels are controlled, gated pores through membranes.

Figure 5 A simplified picture of the production of a proton gradient and then of ATP by the action of light or oxidation of organic molecules inside a membrane. The gradient or ATP is then connected (X) to aqueous phases when ion (M) exchange across membranes can be driven, indicated by = , the symbol for a condenser.

Figure 5 A simplified picture of the production of a proton gradient and then of ATP by the action of light or oxidation of organic molecules inside a membrane. The gradient or ATP is then connected (X) to aqueous phases when ion (M) exchange across membranes can be driven, indicated by = , the symbol for a condenser.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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