Summary Table: Comparison of Different Types of Transport
|
Type of Transport |
Type of Protein |
Direction X Moves |
Source of Energy to transport X |
Example(s) |
|
Name |
Function |
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1 |
Simple Diffusion |
None |
Down its gradient |
Gradient of X |
Restricted to very small molecules and hydrophobics |
How C02 enters RBC |
2 |
(Facilitated) diffusion through a Channel |
Transmembrane channel |
down its |
gradient of X |
water channels in kidney & RBC; many types of ion channels |
control vol. of urine & RBC; flux of ions |
3 |
Facilitated Diffusion using a carrier protein; also called 'carrier mediated transport' |
Carrier or Permease |
down its |
gradient of X |
Glucose transporter in many plasma membranes |
How Glucose exits epithelial cells to body; enters adipose tissue |
RBC anion Exchanger* |
Maximizes CO2 transport by blood |
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4 |
Primary (Direct) Active Transport |
Pump |
up its gradient |
ATP |
Na+/K+ pump |
Maintain high [K+], low [Na+] in cells |
5 |
Secondary (Indirect) Active Transport |
Pump or co-transporter |
up its gradient |
Not ATP (directly): usually a gradient of some substance other than X |
Glucose/Na+ Co-transport |
How Glucose enters epithelial cells from lumen |
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* In some older books band 3 protein is called an anion channel. It is now clear it transports ions but is not a channel. |