1. The Plasma Membrane
AP Biology

2. Selective Permeability
Brings in certain substances
Releases or keeps out certain substances
Maintains water balance
Essential for life

3. Structure of the membrane
Composed largely of phospholipids
Arranged in a bilayer
The hydrophilic heads face the outside of the membrane
The hydrophobic tails are inside the membrane away from water

4. Phospholipid Bilayer
Water bathes the outside of the cell and makes up most of the cytoplasm

5. Fluid Mosaic Model
The membrane has a fluid quality: will ooze if punctured
Parts move and interact
Mosaic means many parts or components

6. Components of the Mosaic
Phospholipids
Glycolipids
Sterols
Proteins
Glycoproteins

8. Types of Proteins Transport proteins Receptor proteins
Recognition proteins
Adhesion proteins
Cell to cell communication proteins

10. Transport Proteins
Allows water soluble molecules to move through membrane
Binds substance on one side, and releases it on the other
Glucose, ions, large polar molecules
May be active or passive

11. Receptor Proteins
Bind substances outside the cell which triggers some cellular activity
Hormones
Perfect fit: lock and key

12. Recognition Proteins Identify each person’s cells as their own
Must be matched in transplants, blood transfusions, etc.

13. Adhesion Proteins
Help cells of the same type stick together in tissues
These are glycoproteins with oligosaccharides attached.

14. Cell to Cell Communication Proteins
Cell to cell communication proteins: match up with another cell to pass on a signal

15. Permeability Some substances move across easily
These include substances which are soluble in lipids (non-polar) CO2, O2, and some H2O.

16. Permeability
Glucose, amino acids, and other large molecules that do not dissolve in lipids cannot pass through
Most water molecules, and ions such as H+, NA+, K+, and Ca+ cannot pass through
Need transporter proteins