Molecule Movement Flashcards
Define uniport and contrasport
Uniport - moving one molecule
Contrasport - moving more than one different molecules
Define symport and antiport
Symport - moving in the same direction
Antiport- moving in the opposite direction
Define DeltaS and P in the equation for Vinwards
Delts S = conc gradient across membrane
P = permeability coefficient
What is the partition coefficient?
The measure of how well a substance dissolves in lipid or aqueous.
What does the rate of transport through lipids depend on?
The polarity of a substance, less polar substance will pass through the membrane faster than polar.
What allows for the rapid diffusion of water across a membrane?
Aquaporin molecules. However these molecules only allow for the passage of one water molecule at a time and are too narrow to allow for the passage of hydrated ions
What effects the passive passage of molecules through aqeuous membranes
The size of the molecule. The rate of influx decreases as size increases.
Describe two gated channels
Voltage Gated - The potential difference in or out of the cell causes a conformational change
Ligand Gated - Binding of a chemical ligand causes a confromational change.
Give an example of a voltage gated channel
Sodium channels are voltage gates. These are very selective and only allow for the passage of unhydrated sodium and potassium ions.
Describe some of the features of facilitated diffusion (carrier mediated transport)
It requires a specific substance to bind to a carrier which causes a confromational change allowing for the substance to pass through the molecule.
However this type of transport can saturate as time is required for the carrier protein to open.
Describe some of the features of active transport
It requires energy to transport molecule against a conc gradient and is key where specific ion concs must be maintained. Can be primary or secondary
Describe Primary active transport and give some examples.
It uses energy sources directly. Ca (ion) ATPase - present on cell membrane and the sarcoplasmic reticulum of muscle fibres. Maintains low Ca concs
H (ion) ATPase - found in parietal cells of gastric glands and intercalated cells of renal tubules. It concentrates H+ ions.
Describe some of the features of Secondary active transport and give an example
It uses an indirect source of energy. Example -
Sodium creates a high electrochemical energy due to pressure to diffuse through the membrane. Sodium and a second molecule bind to the symporter and are both transported into the cell using sodium electochemical energy.
Describe the role of the sodium/potassium pump in maintaing cell volume
Cell membrane isn’t permeable to Na but small amount do leak into cells. This must be removed or the cell would burst.
Phosphorylation of an ATP molecule causes a conformational change that causes 3 x Na ions to extrude across the membrane and 2 x K ions to be introduced into the cell.
