Plasma and Membrane Transport

Lecture: Plasma Membrane and Transport

I. Structure of the Plasma Membrane

A. plasma membrane - the surface encapsulating a cell

B. Fluid Mosaic Model

1. bilayer of phospholipids

a. hydrophilic heads - P04 end "water" "loving" attracted to water on inner/outer parts of cell

b. hydrophobic tails - fatty acids "water" "fearing" attracted to each other on inside of bilayer

c. glycolipids - some carbohydrates attached to outer lipids (involved in cell to cell recognition)

d. cholesterol - regulates fluidity of membrane

2. proteins interspersed throughout the membrane a. functions of membrane proteins i. receptors - hormones, neurotransmitters ii. enzymes - reactions in & out of cell iii. transport - ions and molecules

b. integral proteins - inserted into the bilayer i. transmembrane - across entire bilayer

c. peripheral proteins - on inner & outer surface

d. glycoproteins - carbohydrates on outer surface i. glycocalyx - outer carbohydrate coat (cell recognition and identification)

3. plasma membrane is fluid: it can easily shift & flow

a. two layers can slide over one another b. some proteins float freely throughout membrane c. many proteins attached to cytoskeleton i. allows for regional specialization

4. Features of Plasma Membrane

a. microvilli - fingerlike extensions of cell i. found in kidney and intestine ii. increases surface area for absorption iii. actin filaments for support

b. tight junctions - cell-cell adhesion proteins i. generally at surface of epithelium ii. prevent passage