V. Plasma Membrane- all cells have them- complex, dynamic structures, not passive- differentially permeable

A. Functions1. Regulates the movement of molecules into and

out of the cell2. Site of cell recognition and communication

B. Structure (Fluid mosaic model) (10nm.)1. Phospholipids

a. 5 - 10 different typesb. Most common = phosphotidylcholinec. Membrane fusion easily accomplished

2. Cholesterol - decreases fluidity of membrane

Membrane Fluidity

• Why is it that membrane phospholipids drift laterally, and rarely flip?

How is this fluidity maintained?

• Kinks in unsaturated fatty acid tails of phospholipids.

Cholesterol

3. Proteins a. Integral proteins

-part or all the way through membrane (some move like icebergs)b. Peripheral proteins - usually bound to integral proteins (inside surface)

4. Glycoproteins and glycolipids - cell recognition- external surface oligosaccharides (<15 units)

C. Transport across the membrane1. Diffusion

• movement of molecules down the concentration gradient

• passive process - energy from kinetic energy of molecules

a. Channel proteins - aqueous channel for ions, gated

b. Facilitated diffusion - molecule binds to protein and is transported across membrane

i. Protein changes its shapeii. Specificity

Animation

c. Osmosis - diffusion of water through a selectively permeable membrane

• Know and understand these terms = isotonic, hypertonic, hypotonic, water potential, turgor, plasmolysis

Osmotic Pressure

2. Active transporta. Movement of molecules up the

concentration gradientb. Requires energy (ATP)c. E.g. sodium-potassium pump

3. Cotransport - transport of one solute coupled to transport of another

4. Endocytosis - movement of large molecules (proteins, polysaccharides) through membrane by forming vesiclesa. Phagocytosis - chunks

b. Pinocytosis - droplets

c. Receptor-mediated endocytosis - receptor-covered depressions (coated pits) form coated vesicles (“ligand”=molecule grabbed on to)

5. Exocytosis - waste removal or secretion

• Receptor-mediated Endocytosis