chapter five membranes Flashcards
equilibrium & homeostasis
NOT the same thing
plasma membrane
control of material exchanges, mediation of cell environment interactions
what does the plasma membrane help us understand?
how things get from inside to outside and outside to inside through the layer (membrane)
diffusion
movement of a substance from high substance concentration to low substance concentration due to random thermal molecular motion, NO energy (cannot have energy input)
kinetic energy
molecules are moving, absolute zero will get molecules to stop moving, kinetic energy never stops
factors affecting diffusion of a substance across a membrane
temperature (directly), molecular weight (inversely), surface area (directly), gradient (directly), membrane permeability (directly), distance (inversely)
gradient
difference between stuff inside vs outside the cell, no gradient = no diffusion
flux
amount of substance that crosses a defined surface area per unit time (diffusion per time), time matters, matters in how quickly things diffuse
diffusion equilibrium
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
passive transport
no energy, diffusion directly through membrane (proteins are facilitated)
channels
move things, but limited to small things
what allows for the close of the channel?
proteins ability to flex (changing shape)
open channel (leak channel)
remain open most of the time although can close occasionally for brief periods
gated channel
closed most of the time or regulate by the cell, will momentarily open based on gradients & diffusion
what are the three types of gated channels?
stimulus-gated (ligand gated), voltage gated, mechanosensitive
stimulus-gated (ligand gated)
respond to ligand binding (neurotransmitters, hormones)
ligand
anything that binds to a protein and causes a response
voltage gated
respond to changes in membrane potential (action potentials) (electrical state of cell)
mechanosensitive
respond to physical pressure or distortion (tactile)
what kind of bonds to ligands bind in?
weak bonds (hydrogen bonds, ion bonds)
carrier-mediated transport
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
glucose carriers
too big to fit through a channel
saturation
putting more ligands, which increases gradient, does not change the speed of the protein
uniport carriers
only transport one kind of substance (substrate), concentration gradient determines which way it will move
cotransporters
move two or more substances
symport carriers
move two or more substances in the same direction across a membrane