The cell membrane is the packaging that keeps the outside of the cell outside and the inside of the cell inside. It is composed of a special lipid, called phospholipids that arrange themselves into a bilayer.
Phospholipids can be saturated or unsaturated and the amount of each within the membrane keeps the it the right consistency for the cell. Unsaturated phospholipids (blue – below) have kinks in their structure that keep everything spaced out properly while saturated phospholipids let everything pack together more tightly. This ability to change consistency becomes important in helping the cell tolerate changes in temperature.
The cell membrane is studded with proteins along its length that have important roles:
- Protein channels that allow only certain things to enter and exit the cell. These channels give the membrane its characteristic known as selective permeability. Without this feature, vital nutrients and molecules could leak out of the cell. One example is the glucose transporter, which is important in regulating how much glucose there is in your cells.
- Integral proteins embedded in the membrane. These can include:
- Receptors that act like messengers to respond to signals from their environment and other cells.
- Adhesion proteins allow the cell to stick to other cells or their environment and are important in keeping your tissues together.
Many proteins within the cell are anchored to the inside of the membrane to keep them in place to perform their necessary function
You can think of the membrane as the skin of the cell. Just like the skin on your body is complex, the cell membrane is more than just a casing for the cell.