Some Transport Types Simple diffusion (Down a chemical or electrical potential gradient) Facilitated diffusion (Down a chemical or electrical potential gradient) Primary active transport (Against a chemical or electrical potential gradient) Secondary active transport (Against a chemical or electrical potential gradient) Ion channel (Down a chemical or electrical potential gradient, may be gated) Ionophore mediated transport (Down a chemical or electrical potential gradient)

Classes of Transport Uniport Cotransport –Symport –Antiport

Fig 12-43

Aquaporin Six helices per chain Four chains form a pore –Single file, molecules per second Cf s -1 turnover number for catalase –Water flows in the direction of the osmotic gradient

Glucose Transporter 12 transmembrane helices per chain 5 chains form a pore –GluT1 (erythrocytes) K t ~ 1.5 mM –GluT2 (liver and other) K t ~ 66 mM –GluT4 (myocytes and adipocytes) insulin stimulates installation in membrane

Figure 12-27

Box 12-2 figure 1

Chloride-Bicarbonate Exchanger In respiring tissues –CO 2 in by simple diffusion, then HCO 3 - out, Cl - in In lungs –HCO 3 - in, made into CO 2, Cl - out Antiport

Fig 12-28

Active Transport The hydrolysis of ATP or other energy- releasing reaction is required. ATP + H 2 O ADP + P i The energy is required to move against a chemical (concentration) gradient or an electrical (voltage) gradient (the latter usually means both)

Fig 12-30

ATPases P-type –Cation transporters V-type –Proton transporters (acidifiers) F-type –Proton transporters in bacteria, mitochondria, and chloroplasts (also ATP synthases) Multidrug transporter (tumor cells)

Na + K + ATPase P-type 3 Na + for every 2 K + in Fig 12-33

Other P-type systems Plasma membrane Ca + pump –SERCA pump Cotransport systems

Fig Cotransporter can pump to a 30,000 to 1 glucose level!

Other Ion Channels Ligand and Voltage gated –Na +, K +, and Ca ++ –On-off operations Neurons, etc.

Ionophores (Fig 12-37)