* Transporters: These proteins bind to specific molecules and move them across the membrane. They can be further categorized into:
* Carrier proteins: Bind to a molecule on one side of the membrane, undergo a conformational change, and then release the molecule on the other side. They are involved in facilitated diffusion (down the concentration gradient) or active transport (against the concentration gradient, requiring energy). Examples: Glucose transporter, sodium-potassium pump.
* Channel proteins: Form pores through the membrane that allow specific molecules or ions to pass through. They are usually involved in passive transport (down the concentration gradient). Examples: Ion channels, aquaporins (water channels).
* Pumps: These proteins use energy, typically from ATP hydrolysis, to move molecules against their concentration gradient. They are a type of active transporter. Examples: Sodium-potassium pump, proton pump.
It's important to remember that these are just a few examples. Many other proteins play a role in membrane transport, and their specific functions are complex and varied.
