Jean and Felicia

2.4 Membranes

Functions of the plasma membrane:

Holds the cell together Controls what comes in and out (osmosis, diffusion, active transport) Protect the cell Allow cells to be recognized and to recognize others (cell signaling and immunity) Bind to cells and other organism Site for biochemical reaction: (enzyme, areas for reaction)

Membrane and Membrane transports

Phospholipid bilayer: Phosphate fat 2 layers

Hydrophilic phosphate heads are water attracted but Hydrophobic phosphate tails are water repellent

Phospholipids automatically form a liposome (an enclosed sphere) when surrounded by water. (none of the lipid tails are in contact with the water)

The fluid mosaic model: Tells us that the membrane is flexible and adaptable Phospholipids are connected by weak attractions: the cumulative effect = strong membrane membranes have the freedom of movement in a horizontal plane

Phopholipid bilayers: Selectively permeable (controls entry and exit)

Jean and Felicia

Polar heads: attracted to polar charge

Nonpolar tails: repel any charge and prevent passage of ions