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The CELL (You...just a million times smaller)
Membranes

The Plasma Membrane

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  • The plasma (cell) membrane is a membrane that surrounds the cell. It is very important because it regulates what goes in and out of the cells.
  • The cell membrane is made up of two phospholipid layers. The phospholipids have a hydrophilic head (which is attracted to water) and a hydrophobic tail (which doesn't like water). For this reason, the two layers are positioned so that the heads are on the outside and the tails face the inside.
  • The cell membrane is what we call a fluid-mosaic model. By this, we mean that the phospholipid bilayer has proteins flowing up and down through it. These proteins are called transmembrane proteins. Other proteins, known as peripheral proteins, are attcahed to and move on one of the membranes surface. but not through the whole membrane.
  • The cell membrane of red blood cells also has glycoproteins attached to it's surface. These glycoproteins have the antigens for our blood type.

More on membranes

The cell itself isn't the only stucture that has membranes. Some cellular organelles also have membranes around them. For example, the ER, Golgi complex, nucleus, lysosomes, vesicles, vacuoles all have membranes. These membranes break up these organelles into their own compartments and are reffered to as the endomembrane system.