Membrane transport Transmembrane proteins facilitate transport > Transporters and channels provide specificity (selectivity) o Define which substrates are allowed into the compartment 2 types 1) Channel 2) Transporter Channel A Pore in the membrane > Let hydrophilic molecules through Doesn't change conformation although EXTRACELLULAR FLUID Channel protein Solute CYTOPLASM there can be some that are gated Transporters Binding of solute causes conformational change > 2 different conformational changes Carrier protein Solute o Either outwards open or inwards open Concentration gradients > A difference in concentration (a gradient) represents a chemical potential > The process is not unidirectional (when in equilibrium cannot go back) Passive transport > Occurs in a biological system o The plasma membrane is a barrier so a natural conc grad is made o The use of a transporter/channel protein allows diffusion of solute > Net flow of molecules across the membrane until the concentrations outside and inside are equal o (Co=Ci) Sometimes somethings need to be transported against the conc grad > This requires input of energy (ATP) > Active transport Active transporters 2 types 1) Primary- ATP driven pumps 2) Secondary- coupled transporters Primary- ATP driven pumps Many types > P-type pump o P=phosphorylation Use energy in the form of ATP o They are ATPases so they can hydrolyse ATP and use the phosphate that comes from the ATP molecule to phosphorylate themselves and this is the driving force that moves ions across o Only transport ions across membranes > F-type (and V-type) proton pumps o Instead of using energy they make energy Normally found in mitochondrial inner membranes By driving H+ across the membrane they can synthesise ATP o They are ATP synthases ABC transporter o Use ATP (one or two molecules)
o Transport other small molecules across membranes Secondary-coupled transporters > The conc grad using energy can be used to transport the molecules across o A co-transported molecule is in very high conc outside the membrane so it will be transported down the conc grad using the transporter o By doing so it can also move the main transported molecule (ie .solute) o = symports > This can also work in an antiparallel transported molecule co-transported ion lipid bilayer UNIPORT SYMPORT ANTIPORT coupled transport fashion where the co-transported molecule and the transported molecule go in opposite directions= antiport >Energy must be used to create the conc grads before hand and then can actively transport the other molecule ATP- universal energy currency > Hydrolysis of phosphodiester bonds yields energy ATP binding and hydrolysis powers transport > Against a conc grad >Example- removal of toxins by the ABC transporter P-glycoprotein Symporters- active transport ions (H+ or K+ or Na+ or Ca2+) small molecule H+ CYTOSOL ATP ADP P ATP Pi+ ADP ATP ADP + P ATP ADP P-type pump F-type (and V-type) proton pump 1 Example - co-transport of glucose and Na+ o Electrochemical gradient is used to transport glucose against its chemical potential o Active transport of glucose! Antiporters- active transport 1 Example- antiport of