Exam 3

Membranes are basically a lipid substance

Lipids are phospholipids

Forms a lipid bilayer

Membranes contain proteins “protein sandwich model” proteins on outside

“Unit membrane” membranes function as an inseparable unit lie, membranes cannot be partial & still be functional

nonpolar

“polar heads” outside

• characteristics of membranes are “two-dimensional fluids” (lipids and proteins flow laterally) composed of: - Lipid bilayer: “fluid proteins embedded in the lipid bilayer like pieces of mosaic • membranes are asymmetric the two monolayers are composed of different lipids and proteins: - Two “faces” - Exoplasmic face (E face): faces “outside” - Protoplasmic (P faces): also cytoplasmic face (C face): faces “inside”

faces “outside”

Also cytoplasmic face (C face): faces “inside”

carbohydrate chains “antennae” - receptors sensors - environment

holds the bilayer together

animal cell membranes only never plant cell fluidity

all the way through. Many transmembrane proteins are transport proteins that facilitate proteins of chemicals through membrane

small, inorganic molecules (porins, aquaporin) or ions (ion channels) by facilitated diffusion

partially or all the way through

one molecule one direction passing by facilitated diffusion

2 molecules, same direction, one passing by facilitated diffusion the other by “piggyback”

2 molecules in opposite directions one passing by facilitated diffusion but generates energy to drive the other by active transport in the other direction

large organic molecules by various mechanisms passing facilitated diffusion or by active transport, except never by ATP hydrolysis

sometimes called simple diffusion to distinguish it from facilitated diffusion (later) - the net, (no energy inherent tendency) movement that results from the random kinetic movement of individual molecules from a region of high to low concentrations

the rate of diffusion is a complex function of: 1. The concentration gradient 2. the “resistance” to flow a complex interaction of such characteristics 2.a) The physical and chemical properties of the medium through which the substance is diffusing (density, visiosity, polarity) 2.b) Molecular weight of the diffusing substance according to Graham’s law rate of diffusion 2.c) Temperature: increases the thermal agitation of all molecules

The membrane protein “facilitated” diffusion through the membrane by opening a “tunnel”

The diffusion of a solvent through a semi-permeable membrane - permeable to the solvent (water solvent can pass through) not permeable to the solute (solute cannot pass through) high to low concentration of water