Some Transport Types

1
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)

2
Classes of Transport

• Uniport
• Cotransport
• Symport
• Antiport

3
Fig 12-43
4
Aquaporin

• Six helices per chain
• Four chains form a pore
• Single file, 5? 108 molecules per second
• Cf. 4? 107 s-1 turnover number for catalase
• Water flows in the direction of the osmotic
  gradient

5
Glucose Transporter

• 12 transmembrane helices per chain
• 5 chains form a pore
• GluT1 (erythrocytes) Kt 1.5 mM
• GluT2 (liver and other) Kt 66 mM
• GluT4 (myocytes and adipocytes) insulin
  stimulates installation in membrane

6
Figure 12-27
7
Box 12-2 figure 1
8
Chloride-Bicarbonate Exchanger

• In respiring tissues
• CO2 in by simple diffusion, then HCO3- out, Cl-
  in
• In lungs
• HCO3- in, made into CO2, Cl- out
• Antiport

9
Fig 12-28
10
Active Transport

• The hydrolysis of ATP or other energy-releasing
  reaction is required.
• ATP H2O ? ADP Pi
• The energy is required to move against a chemical
  (concentration) gradient or an electrical
  (voltage) gradient (the latter usually means both)

11
Fig 12-30
12
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)

13
NaK ATPase

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

14
Other P-type systems

• Plasma membrane Ca pump
• SERCA pump
• Cotransport systems

15
Fig 12-36
Cotransporter can pump to a 30,000 to 1 glucose
level!
16
Other Ion Channels

• Ligand and Voltage gated
• Na, K, and Ca
• On-off operations
• Neurons, etc.

17
Ionophores (Fig 12-37)