Test #2 Study Guide•Plasma membranes: made of lipids, proteins, and carbohydrates, mostly lipids like phospholipids•Selective permeability:plasma membrane allows some substances to cross it more easily than others•Amphipathic:mcl that has both a hydrophilic and hydrophobic region. Ex: phospholipids (center is hydrophobic and head is hydrophilic)•Fluid mosaic model:the membrane is a fluid structure with a mosaic of various proteins embedded in or attached to a double layer (bilayer) of phospholipids•Movement of phospholipids:lipids move laterallyin the membrane (107time per second) and flip-flop rarely, b/c the hydrophilic part must cross the hydrophobic part•FluidityoTemp controls fluidity in membrane, dec in temp membrane becomes more rigidoSaturated hydrocarbon tails make the membrane viscous (thick)oUnsaturatedhydrocarbon tails with kinks make the membrane fluid, have holes and leakyoWant to have a moderate viscosity, so have a mixture of saturated and unsaturated tails and have a cholesteroladded in the membrane tooCholesterol reduces membrane fluidity at moderate temps by reducing phospholipid movement, at low temps it hinders solidification by disrupting the packing of phospholipids•Integral proteins: penetrate the hydrophobic core of the lipid bilayer. Many are transmembrane proteinswhich span the membrane, other integral proteins extend only partway into the hydrophobic core•Peripheral proteins:are not embedded in the lipid bilayer at all, they are appendages loosely bound to the surface of the membrane, often exposed to parts of integral proteins•Transmembrane proteins (Passive transport) – transport specific ionsoAmphipathic – has a region that is hydrophobic and hydrophilic on the same mcl (phospholipids are amphipathic too), stuff on the extracellular side have to be hydrophilic. Internal of the protein is hydrophobic in the center of the mcl which helps it remain stable in the plasma membraneHydrophilic mcls can’t fit through the plasma membrane b/c the inside is hydrophobic, this is where the transport proteins come in to helpThe internal surface of the transport protein has different R-groups which allows the hydrophilic mcls to pass through oMembrane proteins and their functions: transport, enzymatic activity, signal transduction cell-cell recognition, intercellular joining, and attachment to the cytoskeleton and extracellular matrix (pg. 129)oTransport proteinsNonpolar mcls are hydrophobic and cross the membrane easily without the aid of membrane proteins
Polarmcls and ions are hydrophilic and pass through the membrane slowlyHydrophilicmcls can pass through the lipid bilayer by passing though transport proteins, which some have chanzzznel proteinsChannel proteinswhich allow certain mcls use as a tunnel through the membrane•Ion channels,many of which are gated channels which open or close in response to a stimulus.