Transport Across Cell Membranes Flashcards
Non mediated, mediated, active, passive transports
Doesn’t use transport protein, uses transport protein, uses energy to move substance against conc/elec gradient, moves substance down gradient
Non mediated
Non polar and hydrophobic molecules. (O2, CO2, N2, fatty acids, steroids, small alc, NH3, fat soluble vitamins. Important for absorption of nutrients - excretion of wastes
Ion channels
Rapid transport. Channel has water filled pore that shields ions from hydrophobic core.
Ionic selectivity
Specific amino acids lining pore determine selectivity
Gating
Stimuli control opening and closing (voltage, ligand binding, cell volume, pH, phosphorylation
Current fluctuations
Represents conformational changes in channel structure, represents opening and closing of ion channels, current flowing can be measured by patch clamp technique
Transport protein properties
Specificity, inhibition, competition, saturation (Inc concentration decreases binding sites available so less transport)
Facilitated diffusion of glucose
Never equilibrium as kinase reduces conc inside the cell by changing glucose to glucose-6-phosphate. Glucose goes down concentration gradient by transport protein
Actives transport 2 forms
Primary - takes energy directly from hydrolysis of ATP. Typical cell uses 30% of energy on primary transport.
Secondary - energy stored in ionic concentration gradient to drive active transport against gradient
Primary transporter
Na+ binds. ATP hydrolyses (ADP and phosphate) > changes conformation and opens allowing Na+ to leave cell to extracellular fluid. K+ comes in and binds and phosphate leaves and KATPase returns to og state
Secondary transporters
Na+ antiporter/exchanger - Ca2+/H+ pushed out (Na goes down it’s electrical gradient to actively transport Ca against its gradient)
Na+ symporter/cotransporter - glucose or amino acids rush in with Na+ ions
