28-01-2012, 12:43 PM
The Plasma Membrane and Homeostasis
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Homeostasis – Maintaining a Balance
Cells must keep the proper concentration of nutrients and water and eliminate wastes.
The plasma membrane is selectively permeable – it will allow some things to pass through, while blocking other things.
Structure of the Plasma Membrane
Lipid bilayer – two sheets of lipids (phospholipids).
-Found around the cell, the nucleus, vacuoles, mitochondria, and chloroplasts.
-Embedded with proteins and strengthened with cholesterol molecules.
What’s a Phospholipid?
It’s a pair of fatty acid chains and a phosphate group attached to a glycerol backbone.
-Polar (water-soluble) heads face out and the nonpolar fatty acids hang inside.
Membrane Proteins
1. Determine what particles can pass through the membrane.
2. Serve as enzymes (may speed reactions).
3. Act as markers that are recognized by chemicals and molecules from the inside and the outside of the cell (the immune system).
