Inside the Cell Membrane

Fluid Mosaic Model:
- Describes the cell membrane as a dynamic structure composed of various components.
- "Fluid" indicates movement; components are not static.
Phospholipid Bilayer:
- Composed of phospholipids with a polar hydrophilic head and two nonpolar hydrophobic tails.
- Arranges itself to form a bilayer that separates the internal and external environments of the cell.
- Provides flexibility and dynamic movement of membrane components.

Cholesterol Function:
- Acts as a spacer in cold temperatures to prevent packing of phospholipids.
- Connects phospholipids in warm temperatures to maintain structural integrity.

Types of Membrane Proteins:
- Peripheral Proteins: Located on the surface, often involved in cell recognition or as enzymes, not embedded in the membrane.
- Integral Proteins: Span across the membrane, involved in transportation and other critical functions.
- Example: Integral proteins facilitate glucose entry into cells from the bloodstream.

Definition:
- Glycoproteins: Proteins with carbohydrates attached for cell recognition and signaling.
- Glycolipids: Lipids with attached carbohydrates integrated into the cell membrane.
Significance:
- Essential for self/non-self recognition, plays a role in immune function.
- Example in Immunology: CD4 glycoprotein on immune cells helps in cell signaling but also serves as an entry point for the HIV virus.