Biology 11
CELL MEMBRANES
Plasma membrane
Functions
Cell cytoplasm is about 80% WATER
Characateristics of water molecule –
Polar molecule –
Hydrogen bonds --
Special properties of water related to hydrogen bonds
High surface tension –
High heat capacity –
Special properties of water related to charge
Universal solvent –
Water molecules do not readily react with (or dissolve) non-polar
(non-charged) molecules –
FLUID MOSAIC MODEL OF MOLECULAR STRUCTURE OF CELL
MEMBRANE
Membrane is bilayer of phospholipids with associated proteins
phosphate head -
lipid tail –
Cell membrane surrounded by aqueous solution both inside and outside cell
phospholipid bilayer -
proteins -
hydrophilic portions of proteins exposed at surfaces of membrane
hydrophobic portions in middle w/lipid tails
receptor proteins -
transport proteins –
recognition proteins –
adhesion proteins –
THIS IS A FLUID MODEL – MOLECULES IN MEMBRANE MOVE AROUND
CHOLESTEROL IN MEMBRANE INCREASES FLUIDITY
support network of protein fibers just under membrane controls cell shape
CELL MEMBRANE PERMEABILITY
Membrane is FREELY PERMEABLE to some substances -
These molecules move in/out of cell by process of DIFFUSION Passive transport --
OSMOSIS –
SOLUTION = SOLVENT + SOLUTE
solvent =
solute =
concentration =
hypertonic environment effect on cell hypotonic environment –
effect on cell isotonic environment –
effect on cell -
CELL MEMBRANE PERMEABILITY
REGULATED substances
Most molecules cannot diffuse freely across membrane –
Cell membrane is selectively permeable to these molecules –
Require transport proteins
Facilitated diffusion –
Active transport –
Other means of getting substances across cell membrane –
Bulk transport (active transport inside vesicles)
Endocytosis Phagocytosis -
Exocytosis -