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

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

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

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

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

 

* In some older books band 3 protein is called an anion channel. It is now clear it transports ions but is not a channel.