I. The Cell (aka Plasma) Membrane

Overview  Cell membrane separates living cell from nonliving surroundings  Controls traffic in & out of the cell  selectively permeable  allows some substances to cross more easily than others

A. Phospholipids Fatty acid Phosphate 1. Tails: Fatty acid chain  Hydrophobic (water Fearing) 2. Heads: Phosphate and glycerol  Hydrophilic (water loving) 3. Arranged as a bilayer Hydrophobic/hydrophilic

Phospholipids cont. 4. Phospholipids can move laterally and allow small molecules, such as water, pass in and out of the cell as needed. Protein Fluidity

Phospholipid bilayer Bilayer Animation Bilayer Animation polar hydrophilic heads nonpolar hydrophobic tails polar hydrophilic heads

B. Glycolipid 1. Makes the cell membrane more fluid Cholesterol  Without cholesterol, cell membranes would be too fluid and too permeable to some molecules.  Cholesterol Cholesterol

D. Membrane Proteins 1. Proteins determine membrane’s specific functions 2. Membrane proteins: a. peripheral proteins  loosely bound to surface of membrane  cell surface identity marker (antigens) b. integral proteins (transmembrane)  penetrate lipid bilayer, usually across whole membrane  transport proteins

Membrane is a collage of proteins & other molecules embedded in the fluid matrix of the lipid bilayer Extracellular (outside) Cholesterol Cytoplasm Glycolipid Transmembrane proteins Filaments of cytoskeleton Peripheral protein Glycoprotein Phospholipids LABEL THE PARTS Intracellular (inside)

E. Many Functions of Membrane Proteins Outside Plasma membrane Inside Transporter Cell surface receptor Enzyme activity Cell surface identity marker Attachment to the cytoskeleton Cell adhesion

Membrane carbohydrates  Play a key role in cell-cell recognition  ability of a cell to distinguish one cell from another  antigens  important in organ & tissue development  basis for rejection of foreign cells by immune system

G. 4 Functions of the Plasma Membrane 1. Cell signaling between cells. 2. Selective transport of substances into and out of the cell. 3. Adhesion of a cell to other cells. 4. Enclose the cytoplasm and prevent dispersion of organelles.

II. Fluid Mosaic Model A. Proteins embedded in the lipid bilayer can move around and “float” among the lipids = “fluid mosaic.” 1. Some of the proteins form channels and pumps that help to move material across the cell membrane. Fluidity