What are transport proteins and ion channels, and how do they function in the movement of substances across cell membranes?

Transport proteins and ion channels are integral membrane proteins that facilitate the movement of substances across cell membranes.

Transport proteins are responsible for the movement of large or polar molecules across the cell membrane. They bind to specific molecules and undergo a conformational change to transport them across the membrane. There are two types of transport proteins: carrier proteins and channel proteins. Carrier proteins bind to specific molecules and undergo a conformational change to transport them across the membrane. Channel proteins form a pore in the membrane, allowing molecules to pass through.

Ion channels are a type of channel protein that allow the movement of ions across the membrane. They are highly selective and only allow specific ions to pass through. Ion channels are regulated by voltage, ligands, or mechanical stimuli. Voltage-gated ion channels open or close in response to changes in membrane potential. Ligand-gated ion channels open or close in response to the binding of a specific molecule. Mechanically-gated ion channels open or close in response to mechanical stimuli, such as pressure or stretch.

In summary, transport proteins and ion channels play a crucial role in the movement of substances across cell membranes. They are responsible for the selective transport of molecules and ions, ensuring that the cell maintains its internal environment and responds to external stimuli.