Learning Outcomes:

After this lesson, you should be able to:

• List and explain the functions of membrane proteins.
• Describe the specificity, competition, and saturation characteristics of transport proteins.

Channel Proteins

Channel proteins are one or more integral membrane proteins arranged so that they form a tiny channel through the plasma membrane.



The channels are lined with the hydrophobic and hydrophilic regions, with the hydrophilic regions facing inward. Ions and small molecules of the right size, charge, and shape can pass through the channel.

Channel types:

• Leak ion channels (non-gated) are always open and are responsible for the plasma membranes’ permeability to ions at rest.
• Gated ion channels can be open or closed, and some gated channels open or close in response to chemical signals or ligands. These are called ligand-gated ion channels.
  • Other gated channels, open or close when there is a change in the membrane potential, these are called voltage-gated ion channels.

Carrier Proteins

Carrier proteins, or transporters, are integral membrane proteins that move ions or molecules from one side of the plasma membrane to the other. The carrier proteins have a specific binding site to which ions or molecules attach on one side of the plasma membrane.