CELL MEMBRANE Selectively permeable Physical isolation Regulation of exchange with environment Sensitivity Structural support

MEMBRANE STRUCTURE Phospholipids (phosphate group bonded to a diglyceride) – form a bilayer Cholesterol (lipid) Proteins – partially embedded (peripheral) or totally spanning (integral) Carbohydrates – glycocalyx – act as adhesive, receptor area, ID system

MEMBRANE PROTEINS Receptors – receive chemicals at binding site – triggers change in cell activity Channel – allow H2O to get through lipid bilayer Carrier – transport solutes across membrane Enzymes Anchor – attach + stabilize cell membrane Identifier – identifies cell as “self”

MEMBRANE TRANSPORT Can be passive or active

PASSIVE TRANSPORT No energy requirement DIFFUSION The net movement of molecules from >[ ] to < [ ] Determined by lipid solubility (alcohol, fatty acids, steroids, O2, CO2) Molecules move DOWN their concentration gradient

2. OSMOSIS Diffusion of H2O across a membrane H2O moves from areas of high [H2O] to low [H2O] OR low [solute} to high [solute] Isotonic Hypotonic (hemolysis results) Hypertonic (crenation)

3. FACILITATED DIFFUSION Transported molecule binds to receptor site, protein carrier (integral protein) undergoes a conformational change, allowing molecule to enter cell Carriers are specific EX – glucose into cell

ACTIVE TRANSPORT Requires ATP Moves a substance (molecule, ion) against its concentration (or electrochemical) gradient Requires a carrier protein

1. SOLUTE PUMPING Against concentration gradient Movement of most amino acids and ions Requires a carrier protein (specific) EX. Na+/K+ pump (exchange pump)

2. EXOCYTOSIS Secretion of substances from cell Substance is enclosed in a membranous vesicle which fuses with the CM EX. Neurotransmitters, hormones, mucus, etc; ejection of cell waste

3. EXOCYTOSIS A.PHAGOCYTOSIS Type of endocytosis “cell eating” Large external particle (proteins, bacteria, dead cell debris) surrounded by a pseudopod and becomes enclosed in a membranous sac EX. WBCs and macrophages

B. PINOCYTOSIS Type of endocytosis “cell drinking” CM surrounds an external droplet containing small solutes; membrane edges fuse, forming a fluid filled vesicle EX. Absorptive cells of the intestines and kidneys

C. RECEPTOR MEDIATED ENDOCYTOSIS External substances bind to specific membrane receptors and form a “coated pit” EX. Intake of some hormones, cholesterol, iron and others