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 bilayerBilayer Animation

polarhydrophilic

heads

nonpolarhydrophobic

tails

polarhydrophilic

heads

B. Glycolipid1. Makes the cell membrane more fluid

Cholesterol Without cholesterol, cell membranes

would be too fluid and too permeable to some molecules.

Cholesterol

D. Membrane Proteins1. 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

Transmembraneproteins

Filaments ofcytoskeleton

Peripheralprotein

Glycoprotein

Phospholipids

LABEL THE PARTS

Intracellular (inside)

E. Many Functions of Membrane Proteins

Outside

Plasmamembrane

InsideTransporter Cell surface

receptorEnzymeactivity

Cell surface identity marker

Attachment to thecytoskeleton

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 ModelA. 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