2.3 Plasma Membrane

Describe the roles of each of the components of the cell membrane in maintaining the internal environment of the cell.

• Phospholipids have both hydrophilic and hydrophobic regions. The polar hydrophilic phosphate regions of the phospholipids are oriented toward the aqueous external or internal environment, while the nonpolar hydrophobic fatty acid regions face each other within the interior of the membrane.
• Embedded proteins can be hydrophilic (with charged and polar side groups), hydrophobic (with nonpolar side groups), or both.
  • i. Hydrophilic regions of the proteins are either inside the interior of the protein or exposed to the cytosol (cytoplasm).
  • ii. Hydrophobic regions of proteins make up the protein surface that interacts with the fatty acids in the interior membrane.

Describe the fluid mosaic model of cell membranes.

• Plasma membranes consist of a structural framework of phospholipid molecules embedded with proteins, steroids (such as cholesterol in vertebrate animals), glycoproteins, and glycolipids. All of these can move around the surface of the cell within the membrane, as illustrated by the fluid mosaic model.