Final answer:
Passive transport proteins, such as channel and carrier proteins, assist in the transport of substances across the cell membrane without energy. Channel proteins like aquaporins allow selective passage of water, while carrier proteins such as GLUT1 transport glucose molecules via facilitated diffusion.
Step-by-step explanation:
Passive membrane transport proteins are integral to cellular function, assisting in the transport of substances across the cell membrane without the need for energy. One key characteristic of these proteins is their ability to transport substances in a specific direction, based on the concentration gradient.
Channel proteins are one type of passive transport proteins. They form pores in the cell membrane, allowing the selective passage of ions or molecules. Channels typically facilitate the movement of substances from an area of higher concentration to an area of lower concentration. An example of a channel protein is the aquaporin channel, which specifically allows water molecules to pass through the cell membrane efficiently.
In contrast to channel proteins, carrier proteins bind to specific molecules on one side of the membrane, undergo a conformational change, and release the molecule on the other side. This process occurs along the concentration gradient and is also known as facilitated diffusion. Glucose transporters like GLUT1 are carriers that only transport glucose molecules into the cell. These proteins operate bidirectionally, meaning they can transport molecules into or out of the cell, depending on the concentration gradient.
The mechanism of transport for these proteins involves the formation of a substance-protein complex. The carrier protein, upon binding the molecule (substance), diffuses across the membrane to discharge the molecule on the other side. This method does not require energy and exemplifies the principle of passive transport.