Channel Proteins

As you are sitting watching this video, the cells in your nervous systems are sending signals to your brain. To do this, they need to be able to move ions efficiently back and forth across the plasma membrane of the cell. In this animation, we’re going to explore the two mechanisms by which this happens. For our example, we’re going to use sodium and potassium ions. These ions are used by many different cells types in the body, including the neurons in your nervous system. The mechanisms are going to be the same. However, they are going to differ in the direction that they move the ions, and whether the process requires any energy. The first process will be passive, and therefore will not require any energy. In this form of transport, proteins in the cell membrane act as channels, allowing the diffusion of ions from areas of high concentration, to areas of low concentration. For example, when the sodium channel opens, sodium ions move from an area of high concentration outside the cell, to an area of lower concentration inside the cell. The exact opposite happens for the potassium channel, which allows the movement of potassium ions from inside the cell to outside. But what if we want to move ions against their concentration gradient? Meaning from areas of low concentration to areas of high concentration. For that, we need to rely on active transport. Active transport requires energy in the form of ATP. The proteins that conduct this form of transport are often called pumps, because they force ions to move against the gradient. One of the more common examples is the sodium-potassium pump, which moves sodium ions back out of the cell and potassium ions into the cell. By coordinating the activity of these channels, the cell is able to effectively control the movement of ions. The channels allow for the rapid movement of ions across the membrane. And the pump restores the ions to their original positions. This is exactly what happens when the neurons in your body generate a signal to be sent to the brain.

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