Learning About Cell Biology

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The Cell Membrane

Lipids and proteins are what make up the cell membrane, or sometimes called the plasma membrane or phospholipid bilayer. You probably already know that the lipids in a membrane bi-layer line up with the hydrophobic (water hating) tails end to end creating an lipid core, while the hydrphilic (water loving) heads are on opposite sides, which creates a barrier between the inside and outside of the cell.

The current accepted model of the cell membrane is the "fluid mosiac model". Simply put, this describes the behavior of the membrane and implies that it is less like a solid wall and more like a line of pool buoys separating the shallow end from the deep end.

When thought of in this manner is is easy to visualize how things could pass through the cell membrane, it just needs to get past the buoys blocking the way.

The buoys are the hydrophobic tails. Recall from other science classes that "like begets like". Meaning you can mix choclate syrup and milk together to form a homogeneous mixture that looks like brown milk. You cannot mix together oil with water because they have opposite properties.

Both milk and chocolate syrup are hydrophilic, so they mix together fairly easily when stirred vigorously.

Oil and water, on the other hand, have oppostie properties. Water is of course, hydrophilic. While oil is hydrophobic. Oil is a lipid, and the tails that orient themselves tail to tail are also hydrophobic.

It turns out that lipids pass through the phospholipid bilayer because they can get past that lipid buoy blocking the way, while hydrophilic proteins must have some help to make it through, help in the form of a channel or carrier which has both properties of the hydrophilic protein and properties of the hydrophobic lipid.

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