Advanced Biology Chapter 5 Membranes

Biological membranes are fluid layers of lipid. Biological membranes are composed of phospholipid bilayers with hydrophilic, polar heads and hydrophobic, nonpolar, fatty acid tails

Biological membranes are fluid layers of lipid. Phospholipid molecules orient their polar heads toward water and their nonpolar tails away from water. The nonpolar interior of a lipid bilayer impedes the passage of any water-soluble substances through the bilayer

Biological membranes are fluid layers of lipid. A lipid bilayer is stable because water's affinity for hydrogen bonding never stops, and the hydrogen bonding holds the membrane together in a liquid form

Proteins embedded within cell membranes determine their character In the fluid mosaic model, a mosaic of proteins floats in the fluid lipid bilayer Cell membranes are assembled from four components: phospholipid bilayer, transmembrane proteins, interior protein network, and cell surface markers (see page 88)

Functions of the Cell Membrane Six key classes of membrane proteins include transporters, enzymes, cell surface receptors, cell surface identity markers, cell adhesion proteins, and attachments to the cytoskeleton See page 91

Diffusion Random motion of molecules causes a net movement of substances from regions of high concentration to regions of lower concentration, and this movement continues until all regions exhibit the same concentration

Diffusion Each transport protein in the plasma membrane is selectively permeable, and thus only allows certain molecules to diffuse through

Diffusion Solute = Substance being dissolved Solvent = Substance doing the dissolving

Diffusion (Osmosis) Is the diffusion of water across a membrane from high to low

Diffusion All of the following refer to the solution type!! Hypertonic = Is when a cell is placed in a solution where the solution has a higher concentration of solutes. This would cause water to rush out of the cell causing plasmolysis (shrinking of cell)

Diffusion Hypotonic = Is when a cell is placed in a solution where the solution has a lower concentration of solutes. This would cause water to rush into the cell causing either the expansion of the cell or cytolysis (cell destruction)

Diffusion Isotonic = Is when a cell is placed in a solution where the concentration of the solute is the same inside and outside the cell. This causes equilibrium.

Bulk passage in and out of the cell Endocytosis occurs when the plasma membrane envelops food particles and brings them into the cell interior. Three major forms of endocytosis are phagocytosis, pinocytosis, and receptor-mediated endocytosis

Bulk passage in and out of the cell Exocytosis refers to the discharge of materials from vesicles at the cell surface

Facilitated Diffusion Facilitated diffusion occurs as molecules move from an area of higher concentration to an area of lower concentration via specific carriers The essential characteristics of facilitated diffusion are specificity, passiveness, and saturation

Passive Transport vs. Active Transport Requires no energy (ATP) to be expended Diffusion Osmosis The movement of a solute across a membrane against its concentration gradient, requiring the use of protein carriers with the expenditure of ATP

Sodium/Potassium Pump Actively transports sodium and potassium ions. 2 K+ in at a time and 3 Na+ out at a time. The movement of these ions results in establishing the charge difference b/w the nerve cell interior and exterior on which all nerve conduction depends.