transport Flashcards
what is diffusion defined as?
the net movement of molecules (simple) of ions (facilitated) from a region where they are highly concentrated to one where their concentration is lower until evenly distributed
which molecules pass across the membrane via simple diffusion?
small, non-polar (lipid soluble) molecules such as oxygen and carbon dioxide
what does the ‘passive’ part mean in diffusion?
energy comes from the natural, inbuilt motion of particles, rather than an external source such as ATP.
what is simple diffusion?
the net movement of small, uncharged (non-polar) molecules from a region where they are highly concentrated to a region where their concentration is lower until they are evenly distributed
what is facilitated diffusion?
the net movement of larger, charged ions and polar molecules from a region where they are more highly concentrated to a region where their concentration is lower until they are evenly distributed, by using channel and carrier proteins that span the membrane.
how are simple and facilitated diffusion similar?
-both passive process so relies only on the inbuilt KE of the diffusing molecules (NO ATP)
what do channel proteins do?
allow specific water-soluble ions to pass through
in channel proteins, how do ions cross the membrane ?
channels are selective, each opening in the presence of a specific ion so there is control of entry and exit of ions
The diffusion of these ions does not occur freely, most channel proteins are ‘gated’, meaning that part of the channel protein on the inside surface of the membrane can move in order to close or open the pore
in carrier proteins, how do molecules cross the membrane?
when a molecule such as glucose that is specific to the binding site of the protein is present, it binds to the protein.
This causes the protein to change shape (orientation) in a way that the molecule is released to the inside of the membrane
what would the rate of facilitated diffusion be limited by?
-number of carrier/ channel proteins
-conc gradient
what is active transport?
the movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using ATP and carrier proteins.
describe direct active transport of a single molecule or ion?
-specific molecule or ion which is complementary to the carrier protein binds to its receptor site
-carrier protein changes shape / orientation due to the hydrolysis of ATP into ADP and Pi, moving the molecule to the other side of the membrane
-the phosphate molecule is released from the protein, which causes the protein to revert to its original shape to repeat the process.
