chapter five membranes

NOT the same thing

control of material exchanges, mediation of cell environment interactions

how things get from inside to outside and outside to inside through the layer (membrane)

movement of a substance from high substance concentration to low substance concentration due to random thermal molecular motion, NO energy (cannot have energy input)

molecules are moving, absolute zero will get molecules to stop moving, kinetic energy never stops

temperature (directly), molecular weight (inversely), surface area (directly), gradient (directly), membrane permeability (directly), distance (inversely)

difference between stuff inside vs outside the cell, no gradient = no diffusion

amount of substance that crosses a defined surface area per unit time (diffusion per time), time matters, matters in how quickly things diffuse

state in which the diffusion fluxes in opposing directions are equal, resulting in a new flux of zero, membrane is a barrier from the inside cell to the outside cell and we need to get things across

no energy, diffusion directly through membrane (proteins are facilitated)

move things, but limited to small things

proteins ability to flex (changing shape)

remain open most of the time although can close occasionally for brief periods

closed most of the time or regulate by the cell, will momentarily open based on gradients & diffusion

stimulus-gated (ligand gated), voltage gated, mechanosensitive

respond to ligand binding (neurotransmitters, hormones)

anything that binds to a protein and causes a response

respond to changes in membrane potential (action potentials) (electrical state of cell)

respond to physical pressure or distortion (tactile)

weak bonds (hydrogen bonds, ion bonds)

transmembrane, but will never be open to both sides of the membrane at the same time, never create a continuous pathway, can take in slightly larger things than channels

too big to fit through a channel

putting more ligands, which increases gradient, does not change the speed of the protein

only transport one kind of substance (substrate), concentration gradient determines which way it will move