Final answer:
Carrier proteins facilitate the transport of substances across a cell membrane by changing shape, and can be involved in passive or active transport. Ion channels are protein pores that allow ions to flow in response to concentration gradients, playing a vital role in various physiological processes.
Step-by-step explanation:
Carrier Proteins
Carrier proteins are integral membrane proteins that facilitate the transport of specific substances across a cell membrane. They change shape as they bind to a target molecule on one side of the membrane, effectively shielding it from the hydrophobic core of the lipid bilayer. Subsequently, the carrier protein transitions back to its original shape, releasing the molecule on the other side of the membrane. This process can be passive, moving substances down their concentration gradient, or active, requiring energy to move substances against their concentration gradient.
Ion Channels
The role of ion channels is critical in maintaining the proper electrochemical gradients of ions across cell membranes. These protein structures form pores through which ions can passively flow in response to a gradient of charge or concentration. Ion channels are necessary for a variety of physiological processes, including nerve impulse transmission, muscle contraction, and the regulation of hydration across cell membranes.