1. Structure and Function
Cell Membrane
Structure and Function

2. Function of the Cell Membrane
The cell membrane has a number of important functions, it:
separates the cell interior (protoplasm) from its external environment (extracellular fluid – ECF)
acts as a selective barrier to control the movement of material into and out of the cell
plays a role in cell behavior and the organization of cells within tissues.

3. Cell Membrane Structure
The structure (chemical composition) of the cell membrane determines function
The cell membrane is a dynamic fluid structure capable of movement and flexibility while the cell carries out cellular functions.

4. Phospholipid Bilayer
hydrophilic phosphate head and hydrophobic tails of the fatty acids of a phospholipid form a basic component of the cell membrane
The water soluble heads of a double layer of phospholipids face the aqueous cytoplasm and ECF while the hydrophobic tails of the fatty acids face inward

5. Phospholipid Bilayer

6. Cholesterol
Cholesterol molecules have several functions in the membrane:
animal cell membranes contain cholesterol linking the fatty acids together and so stabilizing and strengthening the membrane.
They immobilize the first few hydrocarbon groups of the phospholipid molecules making the lipid bilayer less deformable and decreases its permeability to small water-soluble molecules

7. Cholesterol in Cell Membrane

8. Protein Molecules
integral proteins span from one side of the phospholipid bilayer to the other
peripheral proteins sit on one of the surfaces
Proteins comprise about 50% of the mass of membranes, and are responsible for most of the membrane's properties.

9. Internal Peripheral Proteins
Protein inside surface of cell membranes are often attached to the cytoskeleton and are involved in maintaining the cell's shape, or in cell motility. They may also be enzymes, catalyzing reactions in the cytoplasm.

10. External Peripheral Proteins
Proteins on the outside surface of cell membranes can act as receptors by having a specific binding site where hormones or other chemicals can bind. This binding then triggers other events in the cell.
They may also be involved in cell signaling and cell recognition, or they may be enzymes, such as maltase in the small intestine (more in digestion).

11. Carbohydrates
Carbohydrates are found on the outer surface of all eukaryotic cell membranes, and are attached to the membrane proteins or sometimes to the phospholipids.
Proteins with carbohydrates attached are called glycoproteins, while phospholipids with carbohydrates attached are called glycolipids.

12. The carbohydrates are short polysaccharides composed of a variety of different monosaccharides, and form a cell coat or glycocalyx outside the cell membrane. The glycocalyx is involved in protection and cell recognition, and antigens such as the ABO antigens on blood cells are usually cell-surface glycoproteins.

13. Fluid Mosaic Model of Cell Membrane

14. Liposomes
Liposomes are artificial lipid vesicles that function like cell membranes because they can fuse with a cell membrane and deliver their contents directly into the cell
They are used to deliver cancer fighting drugs to specific cells reducing side effects
They may also be a tool in delivering DNA to cells as part of gene therapy

15. Liposome