The Cell Membrane
BASIC CELL MEMBRANE STRUCTURE
I. NOTES
The basic unit of the cell membrane is a macromolecule called a phospholipid.
A phospholipid is has two distinct regions that interact differently with water. The "head," region of the
phospholipid is described to be "hydrophlic," which is translated as being "water loving," while the tail region of the phospholipid is described to be "hydrophobic," which is translated as being "water fearing." In other words, the head region of the phospholipid is attracted to water, while the phospholipid's tail region is repelled by water. As a result, the many, many phospholipids that make up the cell membrane, orient themselves in a way so that the hydrophilic head will be next to water while the hydrophobic tails will be away from water. The only way this can occur is if the phospholipids arrange themselves in two layers. In fact, the cell membrane is best described as being a phospholipid bilayer.
Small molecules are able to pass through the cell membrane. Water, though it is small, is very polar and is only able to pass through the cell membrane due to a the presence of a protein channel called aquaporin which was discovered by Peter Agre in 2003.
CROSS SECTION OF A PHOSPHOLIPID BILAYER
THE ARRANGEMENT OF PHOSPHOLIPIDS IN
A CELL MEMBRANE
PROTEIN CHANNELS
Embedded within the cell membrane are various protein channels that will allow either very charged or very large molecules into or out of the cell. However, only specific molecules are allowed through the protein channels. The term semi-permeable accounts for the fact that the cell membrane will not allow all molecules to come into the cell. The cell membrane will only allow particular molecules pass into or out of the cell.
The cell membrane will only allow particular molecules pass into or out of the cell. The protein channels are either classified as integral (internal) protein channels or as peripheral(external) protein channels. Integral protein channels are either partially or fully embedded into the cell membrane. Peripheral protein channels are lying either on the exterior or interior surface the cell membrane.
Another characteristic of the cell membrane is the presence of carbohydrate molecules which serve as identification markers between cells.
FLUID MOSAIC MODEL
The Fluid Mosaic Model states that each individual component of the cell membrane is completely independent of each other. In other words, the cell membrane is dynamic! All the phospholipids are constantly moving along the plane of the cell membrane as well as the protein channels. Thus the name fluid mosaic is a very apt name in describing the nature of the cell membrane. Fluid meaning that the membrane is constantly in motion. Mosaic meaning that the cell membrane is composed of many individual pieces that make up the whole.
CELLULAR HUMOR!!!!
